Flow cytometer

Abstract

To improve the structure and operation of subassemblies of a flow cytometer.SOLUTION: A flow cytometer includes: a laser diode-based optical subsystem for impinging a beam of light upon particles passing through a viewing zone; a composite microscope objective for gathering and imaging light scattered from or fluorescence emitted by particles passing through the viewing zone; a fluidic subsystem for supplying a liquid sheath flow to the viewing zone; a peristaltic pump for injecting into the liquid sheath flow a liquid sample flow carrying particles that passes together with the liquid sheath flow through the viewing zone; a multimode optical fiber that receives scattered light and fluorescence from the viewing zone that the composite microscope objective gathers and images; and a wavelength division multiplexer for optically separating into color bands light received via the optical fiber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to the field of flow cytometry, and more particularly to the structure and operation of an improved flow cytometer having various individual subassemblies contained therein. [Background technology]

[0002] Flow cytometry is a biophysical technique used in cell counting, sorting, biomarker detection, and protein engineering. In flow cytometry, cells suspended in a liquid stream are passed by an electronic detection device. Flow cytometry allows simultaneous multiparameter analysis of the physical and / or chemical characteristics of up to thousands of cells per second.

[0003] Flow cytometry has a variety of applications in the fields of molecular biology, pathology, immunology, plant biology, and marine biology. It also has a wide range of applications in medicine, particularly in transplantation, hematology, tumor immunology and chemotherapy, prenatal diagnosis, genetics, and sperm sorting for sex preselection. In marine biology, the autofluorescence properties of photosynthetic plankton can be exploited by flow cytometry in characterizing abundance and community composition. In protein engineering, flow cytometry is used with yeast and bacterial display to identify cell surface-displayed protein variants with desired properties. A common variation of flow cytometry is the physical sorting of particles based on their properties, thereby purifying a population of interest.

[0004] The overall flow cytometry system includes the following major components: 1. A flow cell in which a liquid stream, usually referred to as sheath flow, liquid, or fluid, carries and hydrodynamically aligns cells or particles as they pass through a single file in the flow cell; 2. Detect cells or particles passing through the flow cell, typically a. An impedance or conductivity measurement subsystem; or b. an optical illumination subsystem having a light sensing subsystem; a measurement subsystem coupled to the flow cell, 3. A conversion subsystem for converting the output signal from the measurement subsystem into computer processable data; 4. A computer for analyzing the data generated by the conversion subsystem.

[0005] The optical illumination subsystem provides a collimated and then focused light beam, usually a single wavelength laser light, that is incident on the hydrodynamically focused liquid stream passing through the flow cell. Thus, the flow cytometer system 1. one or more lamps, e.g. mercury or xenon; 2. One or more high power water-cooled lasers, e.g., argon, krypton, or dye lasers; 3. One or more low power air-cooled lasers, such as Argon (488 nm), Helium Neon (Red - 633 nm), Helium Neon (Green) and Helium Cadmium (UV), and / or 4. One or more diode lasers (blue, green, red, violet) The optical fiber has one or more light sources including:

[0006] The optical sensing subsystem includes one or more detectors that are aimed at the location where the focused liquid stream passes through the optical beam. Such detectors include: 1. A detector (forward scatter, or FSC) collinear with the light beam; 2. A detector perpendicular to it (side scatter, or SSC), 3. A fluorescence detector; Includes.

[0007] Each suspended particle passing through the beam scatters light, and fluorescent material present in or attached to the particle that is excited by the incident light emits light at wavelengths longer than that of the incident light. By detecting and analyzing the change in brightness in the combination of scattered and fluorescent light at each detector (one for each peak of fluorescent emission), various types of information about the physical and chemical structure of each individual particle can be derived. FSC correlates with the volume of the cell. SSC is due to scattered light from internal components within the cell and depends on the internal complexity of the particle (i.e., the shape of the nucleus, the amount and type of cytoplasmic granules, or the roughness of the membrane). Some flow cytometers omit the fluorescence detector and detect only the scattered light. Other flow cytometers form an image of the fluorescence, scattered, and transmitted light of each cell.

[0008] The conversion subsystem of the flow cytometer system, which may include one or more amplifiers, which may be either linear or logarithmic, generally includes one or more analog-to-digital converters ("ADCs") for converting the output signal of the measurement subsystem into data that is then processed by a computer.

[0009] Modern flow cytometers usually contain up to four lasers and multiple fluorescence detectors. Increasing the number of lasers and detectors allows cell labeling with several different antibodies, allowing target populations to be more precisely identified by their phenotypic markers. Some instruments can further capture digital images of individual cells, which allows analysis of the location of the fluorescent signals inside the cells or on the cell surface.

[0010] Sample Illumination In most instruments, particles of interest, such as blood cells or microspheres, are carried by a sheath flow using hydrodynamic focusing into an observation zone inside a cuvette or jet stream, where they are illuminated by a focused laser beam. This technique provides a means to accurately identify and count particles of interest without being hindered by background noise occurring outside the recording time window (Practical Flow Cytometry, Howard M. Shapiro, Wiley (2003) ISBN 0471411256). To increase detection sensitivity, the cross section of the focused laser beam is usually elliptical with the minor axis along the flow direction. To maintain threshold integrity, the laser profile needs to have a smooth or bell-shaped profile along the flow direction. One common method for generating such a beam is to elongate a nearly collimated circular Gaussian beam along the flow direction by a beam expander made of a prism or a cylindrical lens pair, and then focus the beam by a spherical lens. Since the shape of the beam at the focus is the spatial Fourier transform of the beam in the far field, this produces a Gaussian elliptical spot with its minor axis along the flow.

[0011] Traditional lasers are expensive, bulky, and low-power. More recently, laser diodes ("LDs") have become available. Unlike traditional lasers, next-generation LDs are cost-effective, compact, and power-saving, and therefore hold promise for the next generation of compact biomedical devices. LDs emit light with an elliptical cross-section with the major axis of the ellipse, often called the fast axis, perpendicular to the LD junction, and the minor axis of the ellipse, often called the slow axis, parallel to the LD junction. Unfortunately, the beam quality of a typical LD, especially along its fast axis, is often lacking, thus preventing its widespread adoption in flow cytometry applications.

[0012] Basically, the quality of LD beams can be improved to a great extent by spatial filtering. If a small pinhole or a single-mode optical fiber is positioned at the focal point of a lens to receive only the lowest dimensional spatial mode, the beam passing through the pinhole or single-mode optical fiber has a nearly perfect Gaussian shape. US Patent No. 5,788,927 (Patent Document 1) discloses that such a beam can then be collimated, expanded in the direction of flow through the cytometer, and finally focused into an elliptical Gaussian beam with its minor axis along the flow direction. However, the size of the desktop instrumentation constrains the pinhole diameter to less than 5 microns. The core size of a visible wavelength single-mode optical fiber has similar dimensions. Attempting to manufacture such precision spatial filters and maintain their long-term stability not only increases the cost of LD-based laser systems, but also reduces their reliability.

[0013] More recently, in an effort to reduce possible side lobes due to edge effects of the limited numerical aperture of the collimating lens, U.S. Pat. No. 6,713,019 ("'019 patent") discloses rotating the LD by 90 degrees so that the slow axis is parallel to the flow direction. A beam spreading section, such as a cylindrical concave lens, is then introduced to spread the collimated beam in a direction perpendicular to the flow, and then a beam spot forming section, such as a spherical focusing lens, is introduced to form an elliptical spot in the particle observation zone of the cytometer. As described in detail in the '019 patent, the laser beam after the spot forming section is highly distorted. Specifically, the beam width in the observation zone perpendicular to the flow is equal to or wider than the width of the flow channel. This not only reduces the amount of laser energy incident on the particle, and thus the signal intensity, but also increases the undesirable background scattering from the liquid-flow cell interface. Instead of rotating the LD, U.S. Patent Nos. 7,385,682 and 7,561,267 disclose the use of large numerical aperture aspheric lenses for collimation of the LD. However, such designs cannot correct the interference fringe effect inherent in the beam profile of the LD. Therefore, there is currently a need for a simple LD-based optical system for use in flow cytometers that can reliably generate a focused elliptical beam with an approximately Gaussian shape along the minor axis and width along the major axis.

[0014] Observation Zone Microscope Objectives Modern flow cytometers include a spatial filter, usually consisting of either a mechanical pinhole or a large-core optical fiber, placed at the imaging position of the objective to avoid unwanted background light from entering the cytometer's detector. Since particles remain within the observation zone of the cytometer for a few microseconds, it is necessary to use a microscope objective with a large numerical aperture to maximize light collection efficiency. It is also desirable to use an objective with a large field of view to support multiple spatially separated excitation laser beams in a flow cytometer, as disclosed in U.S. Pat. No. 4,727,020. To achieve these goals, U.S. Pat. Nos. 6,5100,07 and 7,110,192 disclose objective designs using improved apochromats with a gel- or epoxy-bonded nearly hemispherical lens as the optical element most proximal to the sample, followed by multiple meniscus lenses. Although such microscope objectives provide both satisfactory numerical aperture and field of view, they significantly degrade image quality, thereby resulting in a loss of image quality. 1. It limits the effective use of spatial filters, and 2. Poor ability to distinguish background light. Moreover, such refractive microscope objectives are bulky, expensive to manufacture, and often exhibit severe chromatic aberrations. To overcome these limitations, Patent Cooperation Treaty ("PCT") Patent Application No. WO 01 / 27590 (Patent Document 8) discloses an alternative objective design based on a spherical concave mirror. This design provides a large numerical aperture and good image quality along the optical axis. However, poor off-axis characteristics make such a design unsuitable for flow cytometers with multiple spatially separated laser beams.

[0015] Sheath Fluid Supply The performance of a flow cytometer is highly dependent on a stable sheath fluid flow. In particular, flow cytometers that have multiple spatially separated excitation laser beams or perform droplet sorting rely on a constant velocity of sheath fluid flow for timing synchronization. As disclosed in U.S. Pat. No. 5,245,318 (Patent Document 9), conventional flow cytometers: 1. Applying a constant air pressure to the sheath fluid reservoir to push the fluid through the flow cell, or 2. Use a vacuum pump to draw fluid from the sheath fluid reservoir through the flow cell. A gas-tight fluid system is used to provide a stable sheath liquid flow.

[0016] These systems are bulky, expensive to manufacture, and prone to failure. More recently, U.S. Patent No. 8,187,888 discloses a sheath fluid subsystem that pumps sheath fluid flow from a sheath fluid reservoir into an observation zone, and a sheath waste pump that pumps sheath waste from the observation zone to a waste tank. Although the disclosed sheath fluid subsystem does not appear to have been used in a flow cytometer where speed is important, the patent claims that the disclosed sheath fluid subsystem overcomes most of the stability deficiencies of conventional sheath fluid flows. 1. a. A fluidic capacitor between the sheath fluid pump and the flow cell; b. Another fluidic capacitor between the flow cell and the waste pump; By damping the pump pulsation by placing 2. A pump controller whose operation is responsive to a pressure sensor that measures the differential pressure between the inlet and outlet of the flow cell. It has been reported that this problem can be overcome by

[0017] The disclosed sheath fluid subsystem has other limitations, for example, the pressure sensor located near the outlet of the flow cell can be a potential source of contamination.

[0018] Peristaltic Pump Sample liquid supply A peristaltic pump is a volumetric pump in which a set of linear or circular moving rollers continuously compress a compressible tube to propel a fluid through the tube. Peristaltic pumps are particularly widely used to pump clean / sterile fluids or aggressive fluids to avoid cross-contamination of exposed pump parts.

[0019] Conventional peristaltic pumps exhibit pulsation due to a temporary increase in tube volume as the compressed tube expands to return to its original shape each time the rollers roll away from the tube near the pump outlet. Pulsation is undesirable for applications that require smooth flow. To date, numerous attempts have been made to reduce pulsation. For example, U.S. Pat. Nos. 3,726,613 and 3,826,593 introduce cam-type pressers that synchronously apply external pressure to the tube to compensate for tube expansion. In U.S. Pat. No. 4,834,630, multiple tubes attached to segmented rollers are joined together by T-shaped connectors at the inlet and outlet of the pump so that pulsation from individual tubes is reduced by averaging. U.S. Pat. No. 7,645,127 proposes placing the pump tube with a slightly larger inner diameter near the inlet so that the reduced pressure of the tube near the pump outlet is compensated by the compression of a larger volume of the tube near the inlet. Both methods either significantly increase the complexity of the peristaltic pump or do not avoid the effects of pulsation.

[0020] Multicolor fluorescence detection In many multicolor fluorescence detection instruments such as flow cytometers (Practical Flow Cytometry, Howard M. Shapiro, Wiley (2003) ISBN 0471411256), the fluorescence emitted from the object of interest is 1. Light is collected by the microscope objective lens, 2. It is re-imaged through a small pinhole or a multimode optical fiber, 3. It is then collimated and separated into multiple color bands, 4. It is finally detected by a photodetector such as a photomultiplier tube (PMT), PIN photodiode or avalanche photodiode (APD).

[0021] Photomultiplier tubes (PMTs) are essentially a special type of electron tube. These "pre-semiconductor era" devices are bulky and expensive. Furthermore, PMTs have lower quantum efficiency and less reproducible spectral response than silicon-based semiconductor detectors, especially in the biologically important red to near-infrared spectral range. Despite these shortcomings, PMTs have excellent noise characteristics. For example, the dark current of a typical 13 mm PMT (e.g., R9305, Hamamatsu Corporation, Japan) is only 1 nA. In comparison, the dark current of an APD is more than 10 times higher, even when its active area is reduced to one-twentieth of that of the PMT. As a result, PMTs are the de facto low-level light detectors in many commercially available fluorescence detection flow cytometers. Only in some scientific applications, where the event rate is low and the dark current can be distinguished by expensive photon counting techniques, have PMTs been replaced by APD detectors (see High-Throughput Flow Cytometric DNA Fragment Sizing, AV Orden, RA Keller, WP Ambrose, Anal. Chem., 2000, 72 (1), p 37-41). More recently, APD arrays in Geiger mode have also been promoted as an alternative to PMTs (e.g. multipixel photon counters from Hamamatsu Photonics, Japan, and solid-state photomultipliers from SensL Inc., Ireland). However, these detectors also had high dark currents and were nonlinear at high event rates.

[0022] The only industry where APDs have seen widespread acceptance is optical communications. 2It is known that if the chromatic aberration is reduced to less than 1 mm, the corresponding dark current drops to the same level as in a PMT. In optical communications, the light is a laser beam from a single-mode optical fiber. Such a beam is easily collimated and then focused on a 1 mm 2 It is noted that the color separation device used in the fluorescence detector described in U.S. Pat. No. 6,683,314 and references therein is almost identical in function and architecture to the wavelength division multiplexer (WDM) widely used in optical communications described in U.S. Pat. Nos. 4,482,994 and 5,786,915. The fundamental reason for avoiding the use of small area APDs in fluorescence detection instruments is the well-known etendue conservation theorem. That is, the fluorescence emerging through a pinhole or a multimode optical fiber is a dispersed source with an etendue several hundred times larger than a laser beam from a single mode optical fiber. This makes it impossible to collimate the beam over long distances without significantly expanding the beam diameter, as shown in FIG. 26. Unfortunately, the larger the beam diameter, the more difficult the technical challenges to focus to a small spot become. Small area APDs have not been considered viable for multicolor fluorescence detection applications because efficient color separation can only be economically achieved with collimated light beams. There is a clear need for a technology capable of collimating large etendue light beams over long distances without significant expansion of the beam diameter. Such a technology would make possible WDM-like devices for fluorescence detection with performance comparable to low-noise semiconductor detectors. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] U.S. Patent No. 5,788,927 [Patent Document 2] U.S. Patent No. 6,713,019 [Patent Document 3] U.S. Patent No. 7,385,682 [Patent Document 4] U.S. Patent No. 7,561,267 [Patent Document 5] U.S. Patent No. 4,727,020 [Patent Document 6] U.S. Patent No. 6,5100,07 [Patent Document 7] U.S. Patent No. 7,110,192 [Patent Document 8] WO 01 / 27590 [Patent Document 9] U.S. Patent No. 5,245,318 [Patent Document 10] U.S. Patent No. 8,187,888 [Patent Document 11] U.S. Patent No. 3,726,613 [Patent Document 12] U.S. Patent No. 3,826,593 [Patent Document 13] U.S. Patent No. 4,834,630 [Patent Document 14] U.S. Patent No. 7,645,127 [Patent Document 15] U.S. Patent No. 6,683,314 [Patent Document 16] U.S. Patent No. 4,482,994 [Patent Document 17] U.S. Patent No. 5,786,915 [Non-patent literature]

[0024] [Non-Patent Document 1] Practical Flow Cytometry, Howard M. Shapiro, Wiley (2003) ISBN 0471411256 [Non-Patent Document 2] High-Throughput Flow Cytometric DNA Fragment Sizing, AV Orden, RA Keller, WP Ambrose, Anal. Chem., 2000, 72 (1), p 37-41 Summary of the Invention

[0025] Disclosure The present disclosure provides an improved flow cytometer that includes a variety of improved components.

[0026] It is an objective of the present disclosure to provide a simple and robust diode laser-based optical system capable of delivering a focused laser beam of elliptical cross-section with a Gaussian-like intensity distribution along the minor axis and a width optimized for flow cytometry applications along the major axis.

[0027] An objective of the present disclosure is an imaging quality microscope objective that is easy to manufacture, has a long working distance, a large numerical aperture, a wide field of view, and minimal chromatic aberration.

[0028] The objective of the present disclosure is a simple fluidics system for flow cytometers that is not only robust, compact, and easy to manufacture, but also capable of supporting speed-critical applications, such as in instruments with multiple spatially separated excitation laser beams or in droplet sorters.

[0029] The objective of the present disclosure is a simple design for a peristaltic pump that can provide highly desirable, pulse-free liquid flow.

[0030] It is an object of the present disclosure to provide a peristaltic pump with minimal pulsation.

[0031] It is an object of the present disclosure to provide a peristaltic pump that is simple to manufacture and operate.

[0032] It is an object of the present disclosure to provide an apparatus capable of collimating a light beam from a distributed light source over long distances without significant expansion of the beam diameter. It is also an object of the present disclosure to provide a WDM system using the above apparatus to split a light beam into multiple color bands. It is further an object of the present disclosure to provide such a WDM system that is compatible with low noise semiconductor detectors. In addition, due to the diversity of fluorescent probes, it is an object of the present disclosure to provide such a WDM system that is reconfigurable.

[0033] Disclosed herein is a flow cytometer that includes: 1. An LD-based optical subsystem for directing a light beam onto a particle passing through an observation zone; 2. A compound microscope objective lens for collecting and imaging light scattered from or fluorescent light emitted by particles passing through the observation zone; 3. A fluidic subsystem for providing a sheath liquid flow to the observation zone; 4. A peristaltic pump for injecting into the sheath liquid flow a sample liquid flow carrying particles that pass through the observation zone together with the sheath liquid flow; 5. A multimode optical fiber for receiving scattered and fluorescent light from an observation zone where the compound microscope objective lens collects and images; 6. Wavelength division multiplexer for optically separating light received via optical fiber into color bands.

[0034] In general, a LD-based optical subsystem according to the present disclosure for illuminating particles passing through an observation zone of a flow cytometer includes: 1. A laser diode with its slow axis oriented parallel to the flow direction; 2. A collimating lens that converts the diverging beam from the LD into a collimated elliptical beam with its major axis perpendicular to the flow; 3. A focusing lens system that reduces the laser beam in the observation zone to an optimal width in the direction perpendicular to the flow; 4. Finally, a high magnification cylindrical focusing element positioned adjacent the observation zone, with the axis of the cylindrical focusing element perpendicular to the flow direction; Includes.

[0035] The high-magnification cylindrical focusing element transposes the far-field profile of the LD along its slow axis to its Fourier conjugate in the observation zone along the flow direction while maintaining the transverse beam profile, making the laser beam profile in the observation zone optimal for flow cytometry applications.

[0036] Compound microscope objectives according to the present disclosure generally comprise: 1. A concave spherical mirror; 2. A transparent aberration compensator; and an observation zone of the flow cytometer is located between the mirror and the plate. Scattered and fluorescent light emitted from the particles in the observation zone is collected by the mirror and reflected back towards the compensator. Optical aberration caused by the mirror is significantly reduced after the light passes through the compensator. In one aspect of the present disclosure, the observation zone is located inside a flow cell provided by a rectangular glass cuvette with a small rectangular channel through which the particle-bearing liquid flows. The concave mirror is made of an optically transparent material such as glass or optical quality plastic, with a plano-convex shape with a highly reflective coating on the convex surface for internal reflection. The plane of the mirror is either gel-bonded or cemented to one side of the cuvette. The plano-aspheric compensator is made of a transparent material such as glass or optical quality plastic, with the plane being gel-bonded or cemented to the opposite side of the cuvette. The plano-convex mirror and the aspheric compensator can also be integrally formed with the cuvette. In yet another aspect of the present disclosure, an observation zone is within the jet stream, and both the concave mirror and the compensator are separate from the observation zone, with the mirror preferably being a concave surface mirror.

[0037] A fluid system according to the present disclosure generally includes a sheath fluid reservoir from which a fluid pump draws sheath fluid. The sheath fluid then flows from the fluid pump to an inlet of a T-connector. One outlet arm of the T-connector connects to a bypass, which returns a portion of the pumped sheath fluid to the sheath fluid reservoir, where it flows into the air in the sheath fluid reservoir. A second outlet arm of the T-connector connects to a sheath path, which includes a reservoir capsule, followed by a particle filter, and then a flow cell. The sheath fluid that leaves the flow cell then flows to a waste tank. The fluid resistance along the bypass is designed to be lower than the fluid resistance along the sheath path. This allows only a small portion of the sheath fluid to pass through the flow cell. It is noted that typical sheath flow rates in flow cytometry applications are tens of milliliters per minute. This bypass thus allows the use of a higher flow rate fluid pump that is not only less expensive and more reliable, but also operates at a higher pulsation frequency that makes it easier to damp. Since the outlet of the bypass path is connected to air, it also functions as a large fluid capacitor to significantly reduce the pulsation of the sheath fluid flowing along the sheath path. During operation, the inlet part of the filter cartridge is filled with air. Thus, the filter cartridge also functions as a fluid capacitor to further reduce the pulsation of the sheath fluid in the flow cell to a negligible level. The large fluid resistance in the flow cell compresses the air trapped near the inlet of the filter cartridge. When the fluid pump is stopped, the compressed air in the filter cartridge that is pushed back towards the sheath fluid reservoir is stored in the reservoir capsule. The size of the capsule is selected so that the trapped air does not reach the T-connector.

[0038] In general, a peristaltic pump according to the present disclosure includes a number of rollers disposed on the periphery of a rotor that move the rollers in a circular fashion within an arcuate track in a housing, and compressible tabs that compress against the track. In one aspect of the disclosure, the track in the housing of the peristaltic pump includes a recess such that the compressible tube is continuously decompressed to full expansion and then compressed to full closure each time one of the rollers moves past the recess. The position and shape of the recess are maintained such that the total liquid volume in the compressible tube from the recess to the outlet of the pump remains substantially constant. The effect of tube expansion as the roller moves past the pump outlet is compensated for by tube compression as a different other roller immediately upstream of the pump outlet moves into the compressed portion of the recess. In another aspect of the disclosure, the track in the pump housing includes a number of recesses, and a number of rollers are provided upstream of the pump outlet to continuously modify tube compression at multiple portions along the compressible tube. The location and shape of the plurality of indentations are designed such that the correction of tube compression in these sections substantially compensates for the effects of tube expansion near the pump outlet. In yet another aspect of the present disclosure, the compressible tube remains completely closed under the rollers except for the inlet and outlet sections. A variable speed motor is used to drive the pump. When the rollers reach the outlet section, the motor rotation is programmably accelerated to compensate for the tube expansion.

[0039] A wavelength division multiplexer ("WDM") according to the present disclosure generally includes at least two optical elements. The first optical element collimates a light beam received from a distributed light source, such as light from a pinhole or from a multimode optical fiber. The first optical element magnifies the distributed light source, for example defined by a pinhole or the core of a multimode optical fiber, into an image having a size similar to the effective cross section of the first optical element, thereby generating a collimated light beam between the first optical element and its image. The second optical element is positioned near the image and relays the first optical element downstream in the optical path with unit magnification. In this way, the second optical element effectively doubles the collimated optical path length. Additional optical elements in the same 1:1 image relay configuration can also be included in the present disclosure to further extend the collimated optical path. The cascaded unit magnification image relay architecture of the present disclosure provides a greatly extended collimated optical path length without significantly expanding the beam. As a result, WDM technology, which is well established in the optical communications industry, can be easily adapted for fluorescence detection. Specifically, multiple color bands present in a light beam are separated using dichroic filters placed along the optical path, and the separated light is tightly focused to a small spot compatible with a low-noise semiconductor photodetector.

[0040] In one embodiment of the WDM, the first optical element is a lens and the second element is a concave mirror. However, it is also clear to one skilled in the art that other types of refractive and / or reflective optical components can be used to achieve the same design goal. Similar to its counterpart in optical communication, the optical path in the WDM of the present disclosure can be folded using dichroic filters. In one embodiment of the present disclosure, the optical path is folded into a zigzag configuration. Preferably, to facilitate reliable reconstruction of the flow cytometer, each dichroic filter is bonded to a mechanical holder with a reference surface optically parallel to the reflective surface of the filter. As a result, all WDM filters can be precisely positioned along the optical path by referencing the filter holder to a common optical plane.

[0041] In another embodiment of the present disclosure, the collimated beam passing through the dichroic filter is further split into multiple color bands using a secondary dichroic filter. It is clear to those skilled in the art that the dichroic filter can be inserted anywhere along the elongated collimated beam path obtained by the relay imaging of the present disclosure, and thus the tightly focused beam can be delivered to the photodetector using various optical configurations, such as the star configuration described in U.S. Pat. No. 6,683,314, the split configuration described in U.S. Pat. No. 4,727,020, and other types of WDM optical configurations widely implemented in the optical communication industry. Instead of a concave mirror, the WDM can be replaced with a curved dichroic filter to further increase the number of color bands selected by the WDM.

[0042] [The present invention 1001] Flow cytometers (40) including: (a) a laser diode ("LD")-based optical subsystem (50) for directing a light beam into an observation zone of a flow cytometer (40) through which a particle-bearing sample fluid flows, the sample fluid being hydrodynamically constricted within the observation zone by a sheath fluid flow also flowing through the observation zone, the optical subsystem (50) comprising: i. an LD for emitting a diverging light beam from an end face of the LD, said diverging light beam having an elliptical cross-sectional profile having both a major axis and a minor axis; ii. a collimating lens for converting the divergent light beam emitted from the LD into a collimated elliptical light beam, the minor axis of the collimated elliptical light beam being oriented parallel to the direction of particle passage through the observation zone; iii. beam compression optics for reducing the size of the elliptical light beam in the observation zone, whereby the width of the major axis of the elliptical light beam oriented perpendicular to the direction of particle passage through the observation zone is less than the width of the sheath liquid flow; v. a cylindrical focusing element positioned adjacent said observation zone, the axis of the cylindrical focusing element being oriented perpendicular to the direction of passage of particles through said observation zone, thereby (1) the minor axis of the light beam is focused in the observation zone; and (2) the magnitude of the major axis of the elliptical light beam in the observation zone remains essentially unchanged; A cylindrical focusing element; an optical subsystem (50) including: (b) a compound microscope objective (60) for imaging light scattered from and fluorescence emitted by particles present within the observation zone, the compound microscope objective (60) comprising: i. a concave boundary onto which the scattered and fluorescent light is incident; ii. an aberration correction plate made from an optically transparent material, said aberration correction plate comprising: (1) The aberration correction plate A. The thinnest and B. has negative optical power; a first zone of the aberration correction plate outside an intermediate zone of the aberration correction plate; (2) a second zone of the aberration correction plate, inside the intermediate zone, having positive optical power; and an aspheric lens having an aberration correction plate, and light reflected from the compound microscope objective lens (60) passes through the aberration correction plate; a compound microscope objective (60) including: a flow cytometer (40) having an observation zone disposed between the concave mirror and the aberration correction plate; (c) a fluidic subsystem (70) for providing a pulsation-free flow of sheath fluid to the observation zone, comprising: 1. a fluid pump for drawing fluid from a reservoir; ii. A T-shaped connector having at least one inlet and two outlets; (1) an inlet of the T-connector receives liquid from the liquid pump; (2) a first portion of the liquid received by the inlet flows through a first one of the outlets and a bypass conduit back to the reservoir; and (3) flowing a second portion of the liquid received by the inlet through a second one of the outlets and through a particle filter to the observation zone of a flow cytometer (40); A T-shaped connector, a fluid subsystem (70) including: (d) a peristaltic pump 80 for supplying a sample liquid carrying particles, the sample liquid being hydrodynamically constricted in the observation zone by a sheath liquid flow, the peristaltic pump 80 comprising: i. a pump housing having an arcuate curved track formed therein extending between a pump inlet and a pump outlet; ii. a plurality of rollers attached to a rotor, said rollers having substantially equal angular spacing between each immediately adjacent pair of rollers, said rotor rotatable with said rollers attached to said rotor inside said pump housing; ii. a compressible tube sandwiched between said roller and said arcuate track of said pump housing, said arcuate track comprising: (1) an outlet section, where as a roller rolls through the outlet section, the compressible tube adjacent the roller expands continuously from a fully closed condition at the beginning of the outlet section to a fully open condition at the pump outlet where the roller loses contact with the compressible tube; (2) at least one pump section along the arcuate track between the pump inlet and the pump outlet, the compressible tube being compressed to a fully closed condition by at least one of the rollers; and a compressible tube comprising: A peristaltic pump 80 including: (e) a wavelength division multiplexer 90 ("WDM (90)") for separating into a plurality of color bands the light beam initially emitted from the observation zone and imaged by the compound microscope objective lens (60) into an optical fiber for transmission to the WDM (90), i. a collimating optic that magnifies the image to produce an image substantially the same size as the effective size of the collimating optic; ii. at least one dichroic filter disposed between said collimating optics and said image, said at least one dichroic filter separating the collimated light beam into two characteristic color branches; iii. a focusing optic disposed within one of said branches, said focusing optic focusing the light beam within said branch to a spot having a diameter of less than 1.0 mm; iv. an image relay optical element disposed adjacent to the image produced by the collimating optical element in the other branch, the image relay optical element producing an image of the collimating optical element at substantially unit magnification; Including, WDM(90). [The present invention 1002] A flow cytometer (40) of the present invention 1001, wherein the cuvette has a rectangular shape, and the observation zone of the flow cytometer (40) is disposed within a flow path having a rectangular cross section disposed within the cuvette. [The present invention 1003] A flow cytometer (40) of the present invention 1001, wherein the cuvette has a tubular cross-section and the observation zone of the flow cytometer (40) is disposed within a flow path having a circular cross-section disposed within the cuvette. [The present invention 1004] The flow cytometer (40) of the present invention 1001, wherein the sample liquid and the sheath liquid flows form a jet flow in which the observation zone of the flow cytometer (40) is disposed. [The present invention 1005] The flow cytometer (40) of the present invention 1002, wherein the cylindrical focusing element is in optical contact with an entrance face of the rectangular cuvette. [The present invention 1006] The flow cytometer (40) of the present invention 1002, wherein the cylindrical focusing element is separated from the rectangular cuvette. [The present invention 1007] The flow cytometer (40) of the present invention 1003, wherein the cylindrical focusing element is separated from the tubular cuvette. [The present invention 1008] The flow cytometer (40) of the present invention 1004, wherein the cylindrical focusing element is separated from the jet stream. [The present invention 1009] The flow cytometer (40) of the present invention 1001 further comprising a polarization adjusting element through which the collimated elliptical light beam passes. [The present invention 1010] A flow cytometer (40) according to the present invention 1001, wherein an optical image of the observation zone is formed outside a compound microscope objective lens (60). [The present invention 1011] A flow cytometer (40) of the present invention 1010, wherein the observation zone is disposed within a flow channel contained within a rectangular cuvette made from an optically transparent material. [The present invention 1012] The flow cytometer (40) of the present invention 1011, wherein the concave mirror is a plano-concave back-surface mirror made of an optically transparent material. [The present invention 1013] A flow cytometer (40) according to the present invention, wherein the plane of the plano-concave back-mirror is optically coupled to the plane of the cuvette. [The present invention 1014] The flow cytometer (40) of the present invention 1013, wherein an optical adhesive material achieves the optical coupling. [The present invention 1015] A flow cytometer (40) according to the present invention, wherein a refractive index matching gel achieves the optical coupling. [The present invention 1016] A flow cytometer (40) according to the present invention 1013, wherein a refractive index matching fluid achieves said optical coupling. [The present invention 1017] The flow cytometer (40) of the present invention 1013, wherein an optical contact junction achieves the optical coupling. [The present invention 1018] A flow cytometer (40) according to the present invention, wherein the plano-concave back-face mirror is integral with the cuvette means. [The present invention 1019] The flow cytometer (40) of the present invention 1011, wherein the aberration correction plate is a flat aspheric lens. [The present invention 1020] A flow cytometer (40) according to the present invention, wherein the plane of the aberration correction plate is optically coupled to the plane of the cuvette opposite the plano-concave back-surface mirror. [The present invention 1021] A flow cytometer (40) of the present invention 1020, wherein a refractive index matching gel achieves said optical coupling. [The present invention 1022] A flow cytometer (40) of the present invention 1020, wherein a refractive index matching fluid achieves said optical coupling. [The present invention 1023] The flow cytometer (40) of the present invention 1020, wherein an optical contact junction achieves said optical coupling. [The present invention 1024] The flow cytometer (40) of the present invention 1020, wherein the plano aspheric lens is integrally formed with the cuvette. [The present invention 1025] The flow cytometer (40) of the present invention 1019, wherein the aberration correction plate is spaced apart from the cuvette. [The present invention 1026] A flow cytometer (40) according to the present invention 1010, wherein the observation zone is inside the jet stream. [The present invention 1027] The flow cytometer (40) of the present invention 1025, wherein the concave mirror is a surface mirror. [The present invention 1028] A flow cytometer (40) of the present invention 1010, wherein the observation zone is disposed on the surface of a flat transparent substrate. [The present invention 1029] The flow cytometer (40) of the present invention 1028, wherein the concave mirror is a plano-concave back-surface mirror made of an optically transparent material. [The present invention 1030] A flow cytometer (40) according to the present invention, wherein the flat surface of the plano-concave back-surface mirror is optically coupled to the flat transparent substrate. [The present invention 1031] The flow cytometer (40) of the present invention 1030, wherein an optical adhesive material provides said optical coupling. [The present invention 1032] A flow cytometer (40) of the present invention 1030, wherein a refractive index matching gel achieves said optical coupling. [The present invention 1033] A flow cytometer (40) of the present invention 1030, wherein a refractive index matching fluid achieves said optical coupling. [The present invention 1034] The flow cytometer (40) of the present invention 1030, wherein an optical contact junction achieves said optical coupling. [The present invention 1035] The flow cytometer (40) of the present invention 1029, wherein the plano-concave back-surface mirror is integrally formed with the flat transparent substrate. [The present invention 1036] The flow cytometer (40) of the present invention 1028, wherein the aberration correction plate is spaced apart from the flat transparent substrate. [The present invention 1037] A flow cytometer (40) of the present invention 1001, wherein the particle filter has an inlet for receiving liquid from the T-connector, and the inlet of the particle filter is positioned such that air is trapped within the particle filter at the inlet. [The present invention 1038] A flow cytometer (40) according to the present invention, wherein air cannot enter the bypass conduit when the liquid pump is stopped. [The present invention 1039] The flow cytometer (40) of the present invention 1038 further comprising a small capsule disposed between a second of the outlets of the T-connector and the particle filter for storing air expelled from the particle filter when the liquid pump is stopped. [The present invention 1040] The flow cytometer (40) of the present invention 1038 further comprising a length of tubing disposed between a second of the outlets of the T-connector and the particle filter for storing air exhausted from the particle filter when the liquid pump is stopped. [The present invention 1041] The flow cytometer (40) of the present invention 1038 further comprising a regulator valve disposed in the bypass conduit between a first one of the outlets of the T-connector and the reservoir to restrict liquid flow between the first outlet and the reservoir. [The present invention 1042] The flow cytometer (40) of the present invention 1038 further comprising an adjustable valve disposed between a second of the outlets of the T-connector and the observation zone to restrict liquid flow between the second outlet and the observation zone. [The present invention 1043] The flow cytometer (40) of the present invention 1038, wherein the throughput of the liquid pump is adjustable. [The present invention 1044] The flow cytometer (40) of the present invention 1001, wherein the arcuate track of the pump housing includes at least two pump sections, and the arcuate track further includes at least one recessed portion disposed between the pump sections along the arcuate track, and when one of the rollers rolls through the recessed portion, the compressible tube in the recessed portion is depressurized to a fully expanded state and then compressed to a fully closed state. [The present invention 1045] A flow cytometer (40) including a plurality of recessed portions along the arcuate track upstream of the pump outlet, wherein the angular spacing between the compressed portion of the recessed portion adjacent the pump outlet and the outlet portion of the arcuate track is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [The present invention 1046] The flow cytometer (40) of the present invention 1044, wherein the compressible portion of the recessed portion adjacent the pump outlet has a shape complementary to the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the total fluid volume within the portion of the compressible tube extending from the recessed portion to the pump outlet remains substantially unchanged. [The present invention 1047] A flow cytometer (40) of the present invention 1044 having a plurality of recessed portions each interspersed between immediately adjacent pairs of a plurality of pump portions. [The present invention 1048] (a) the angular spacing between adjacent pairs of recessed portions; (b) an angular spacing between the exit portion of the arcuate track and a recessed portion adjacent the exit portion; and is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [The present invention 1049] A flow cytometer (40) of the present invention 1047, wherein the shape of the plurality of recessed portions of the arcuate track complements the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the fluid volume within the plurality of recessed portions and the portion of the compressible tube at the outlet portion remains substantially unchanged. [The present invention 1050] A flow cytometer (40) of the present invention 1001, wherein the speed of the rotor is programmably controlled to vary substantially inversely proportional to the rate of change of fluid volume in the compressible tube due to changes in compression of the compressible tube near the exit portion of the arcuate track. [The present invention 1051] A flow cytometer (40) of the present invention 1001, wherein at least one additional dichroic filter is disposed between the image relay optical element and the image produced by the image relay optical element, the dichroic filter generating two branches of the light beam having characteristic colors. [The present invention 1052] A flow cytometer (40) of the present invention 1051, wherein another focusing optical element is disposed within one of said branches to focus said light beam within said branch to a spot having a diameter of less than 1.0 mm. [The present invention 1053] The flow cytometer (40) of the present invention 1052, wherein the sequential combination of image relay optics, dichroic filters, and focusing optics are cascaded to generate additional focused spots having diameters of less than 1.0 mm for multiple color bands of the light beam. [The present invention 1054] A flow cytometer (40) of the present invention 1052, wherein the dichroic filter is assembled using a template including two optically flat glass plates bonded together in optical contact, and the dichroic filter is bonded to a filter holder using the template, such that a coated filter surface of the dichroic filter is recessed relative to a reference surface of the filter holder and optically parallel to the reference surface. [The present invention 1055] A flow cytometer (40) of the present invention 1054, wherein the reference surface of the filter holder rests against an optically flat surface of a reference block contained within a WDM (90), thereby providing consistent optical alignment when installing the dichroic filter within the WDM (90). [The present invention 1056] a laser diode-based optical subsystem (50) for directing a light beam into an observation zone within which particles reside, (a) an LD for emitting a diverging light beam from an end face of the LD, the diverging light beam having an elliptical cross-sectional profile having both a major axis and a minor axis; (b) a collimating lens for converting the divergent light beam emitted from the LD into a collimated elliptical light beam, the minor axis of the collimated elliptical light beam being oriented parallel to the direction of particle passage through the observation zone; (c) a beam compression optic for reducing the size of the elliptical light beam in the observation zone, whereby the width of a major axis of the elliptical light beam directed perpendicular to the direction of particle passage through the observation zone is less than the width of a sheath liquid flow; and (d) a cylindrical focusing element positioned adjacent to the observation zone, the axis of the cylindrical focusing element being oriented perpendicular to the direction of passage of particles through the observation zone, whereby i. the minor axis of the light beam is focused at the observation zone; and ii. the magnitude of the major axis of the elliptical light beam in the observation zone remains essentially unchanged; A cylindrical focusing element; an optical subsystem (50) including [The present invention 1057] The optical subsystem (50) of the present invention 1056 further includes a cuvette having a rectangular cross-section, wherein the observation zone is disposed within a flow path having a rectangular cross-section disposed within the cuvette. [The present invention 1058] The optical subsystem (50) of the present invention 1056 further comprises a cuvette having a tubular cross-section, the observation zone being disposed within a flow path having a circular cross-section disposed within the cuvette. [The present invention 1059] The optical subsystem (50) of the present invention 1056, wherein the sample liquid and sheath liquid flows form a jet stream within which the observation zone is located. [The present invention 1060] The optical subsystem (50) of the present invention 1057, wherein the cylindrical focusing element is in optical contact with an entrance face of the rectangular cuvette. [The present invention 1061] The optical subsystem (50) of the present invention 1057, wherein the cylindrical focusing element is separated from the rectangular cuvette. [The present invention 1062] The optical subsystem (50) of the present invention 1058, wherein the cylindrical focusing element is separated from the tubular cuvette. [The present invention 1063] The optical subsystem (50) of the present invention 1059, wherein the cylindrical focusing element is separated from the jet stream. [The present invention 1064] The optical subsystem (50) of the present invention 1056 further comprising a polarization adjusting element through which the collimated elliptical light beam passes. [The present invention 1065] A method for delivering an elliptical light beam using an LD-based optical subsystem (50), the light beam having a smooth profile at a focus of the short axis of the light beam disposed in an observation zone through which a sample liquid flows, the sample liquid being hydrodynamically constricted within the observation zone by a sheath liquid flow also flowing through the observation zone, the method comprising: (a) providing an LD emitting a diverging light beam from an end face of the LD, the diverging light beam having an elliptical cross-sectional profile having both a major axis and a minor axis; (b) directing the divergent light beam emitted by the LD into a collimating lens for converting the divergent light beam emitted from the LD into a collimated elliptical light beam, the minor axis of the collimated elliptical light beam being oriented parallel to the direction in which the sample liquid passes through the observation zone; (c) directing the collimated elliptical light beam after passing through the collimating lens into a beam compression optical element for reducing the size of the elliptical light beam in the observation zone, whereby the width of the major axis of the elliptical light beam directed perpendicular to the direction of passage of sample liquid through the observation zone is less than the width of the sheath liquid flow; (d) directing the light beam, after passing through the beam compression optical element, onto a cylindrical focusing element positioned adjacent to the observation zone, the axis of the cylindrical focusing element being oriented perpendicular to the direction in which sample liquid passes through the observation zone, thereby: i. the minor axis of the light beam is focused at the observation zone; and ii. the magnitude of the major axis of the elliptical light beam in the observation zone remains essentially unchanged; The process and A method comprising: [The present invention 1066] The method of claim 1065, wherein the observation zone is disposed within a channel having a rectangular cross section disposed within a cuvette. [The present invention 1067] The method of claim 1065, wherein the observation zone is disposed within a channel having a circular cross section disposed within a cuvette. [The present invention 1068] The method of claim 1065, wherein the observation zone is disposed within the jet stream. [The present invention 1069] The method of claim 1066, further comprising the step of establishing optical contact between said cylindrical focusing element and an entrance face of said cuvette. [The present invention 1070] The method of claim 1066, further comprising the step of establishing a gap between said cylindrical focusing element and said cuvette. [The present invention 1071] The method of claim 1067, further comprising the step of establishing a gap between said cylindrical focusing element and said cuvette. [The present invention 1072] The method of claim 1068, further comprising the step of establishing a gap between said cylindrical focusing element and said jet stream. [The present invention 1073] The method of claim 1065, further comprising the step of inserting a polarization adjusting element between said collimating lens and said beam compression optical element, whereby said collimated elliptical light beam passes through said polarization adjusting element. [The present invention 1074] A compound microscope objective (60) adapted for imaging light scattered from and fluorescence emitted by particles present in an observation zone, the compound microscope objective (60) comprising: (a) A concave mirror on which the scattered light and fluorescent light are incident; (b) an aberration correction plate made from an optically transparent material, said aberration correction plate comprising: i. the aberration correction plate is (1) The thinnest and (2) has negative optical power; a first zone of the aberration correction plate outside an intermediate zone of the aberration correction plate; ii. a second zone of the aberration correction plate, inside the intermediate zone, having positive optical power; and an aberration correction plate, wherein light reflected from the compound microscope objective lens (60) passes through the aberration correction plate; wherein the observation zone is disposed between the concave mirror and the aberration correction plate. [The present invention 1075] The compound microscope objective lens (60) of the present invention 1074, wherein an optical image of the observation zone is formed outside the compound microscope objective lens (60). [The present invention 1076] A compound microscope objective (60) of the present invention 1075, wherein the observation zone is disposed within a flow channel contained within a rectangular cuvette made from an optically transparent material. [The present invention 1077] The compound microscope objective lens (60) of the present invention 1076, wherein the concave mirror is a plano-concave back-surface mirror made of an optically transparent material. [The present invention 1078] A compound microscope objective lens (60) according to the present invention, wherein the plane of the plano-concave back-surface mirror is optically coupled to the plane of the cuvette. [The present invention 1079] The compound microscope objective lens (60) of the present invention 1078, wherein an optical adhesive material achieves the optical coupling. [The present invention 1080] The compound microscope objective lens (60) of the present invention, wherein a refractive index matching gel provides said optical coupling. [The present invention 1081] A compound microscope objective lens (60) according to the present invention, wherein a refractive index matching fluid provides said optical coupling. [The present invention 1082] The compound microscope objective lens (60) of the present invention 1078, wherein an optical contact joint achieves said optical coupling. [The present invention 1083] The compound microscope objective lens (60) of the present invention, wherein the plano-concave back-surface mirror is integrally formed with the cuvette means. [The present invention 1084] The compound microscope objective lens (60) of the present invention 1076, wherein the aberration correction plate is a flat aspheric lens. [The present invention 1085] A compound microscope objective lens (60) according to the present invention, wherein the plane of the aberration correction plate is optically coupled to the plane of the cuvette opposite the plano-concave back-surface mirror. [The present invention 1086] A compound microscope objective lens (60) according to the present invention, wherein a refractive index matching gel provides said optical coupling. [The present invention 1087] A compound microscope objective lens (60) according to the present invention, 1085, wherein a refractive index matching fluid provides said optical coupling. [The present invention 1088] The compound microscope objective lens (60) of the present invention 1085, wherein an optical contact joint achieves said optical coupling. [The present invention 1089] The compound microscope objective lens (60) of the present invention 1085, wherein the planar aspheric lens is integrally formed with the cuvette. [The present invention 1090] The compound microscope objective (60) of the present invention 1084, wherein the aberration correction plate is spaced from the cuvette. [The present invention 1091] A compound microscope objective lens (60) according to the present invention 1075, wherein the observation zone is inside the jet stream. [The present invention 1092] A compound microscope objective lens (60) according to the present invention, wherein the concave mirror is a surface mirror. [The present invention 1093] A compound microscope objective lens (60) according to the present invention 1075, wherein the observation zone is disposed on the surface of a flat transparent substrate. [The present invention 1094] The compound microscope objective lens (60) of the present invention 1093, wherein the concave mirror is a plano-concave back-surface mirror made of an optically transparent material. [The present invention 1095] A compound microscope objective lens (60) according to the present invention, wherein the flat surface of the plano-concave back-surface mirror is optically coupled to the flat transparent substrate. [The present invention 1096] The compound microscope objective lens (60) of the present invention 1095, wherein an optical adhesive material provides said optical coupling. [The present invention 1097] A compound microscope objective lens (60) according to the present invention, wherein a refractive index matching gel provides said optical coupling. [The present invention 1098] A compound microscope objective lens (60) according to the present invention, wherein a refractive index matching fluid provides said optical coupling. [This invention 1099] The compound microscope objective lens (60) of the present invention 1095, wherein an optical contact joint achieves said optical coupling. [The present invention 1100] The compound microscope objective lens (60) of the present invention, wherein the plano-concave back-surface mirror is integrally formed with the flat transparent substrate. [The present invention 1101] The compound microscope objective lens (60) of the present invention 1093, wherein the aberration correction plate is spaced from the flat transparent substrate. [The present invention 1102] A method for characterizing a microscopic species using a microscope objective device comprising: (a) A concave mirror; (b) an aberration correction plate made of an optically transparent material, the aberration correction plate being an aspheric lens having a zone of the plate means outside an intermediate zone having a negative optical power, the zone being the thinnest thickness of the plate means, and a zone inside the intermediate zone having a positive optical power; (c) an observation zone disposed between said concave mirror and said aberration correction plate; [The present invention 1103] The method of claim 1102, wherein an optical image of the observation zone is formed outside the device. [The present invention 1104] The method of claim 1103, wherein said observation zone is disposed within a flow channel contained within a rectangular cuvette means made from an optically transparent material. [The present invention 1105] The method of claim 1104, wherein said concave mirror is a plano-concave back-surface mirror made from an optically transparent material. [The present invention 1106] The method of any one of claims 1105 to 1107, wherein a planar surface of said plano-concave back-mirror means is optically coupled to a planar surface of said cuvette means. [The present invention 1107] The method of claim 1106, wherein an optical adhesive material provides said optical bond. [The present invention 1108] The method of claim 1106, wherein an index matching gel provides said optical coupling. [The present invention 1109] The method of claim 1106, wherein an index matching fluid provides said optical coupling. [The present invention 1110] The method of claim 1106, wherein an optical contact bond provides said optical coupling. [The present invention 1111] The method of claim 1106, wherein said plano-concave back-face mirror is integral with said cuvette. [The present invention 1112] The method of claim 1104, wherein the aberration correction plate is a planar aspheric lens. [The present invention 1113] The method of claim 1112, wherein a plane of said aberration correction plate is optically coupled to a plane of said cuvette means opposite said concave mirror. [The present invention 1114] The method of claim 1113, wherein an index matching gel provides said optical coupling. [The present invention 1115] The method of claim 1113, wherein an index-matching fluid provides said optical coupling. [The present invention 1116] The method of claim 1113, wherein an optical contact bond provides said optical coupling. [The present invention 1117] The method of claim 1113, wherein said planar aspheric lens is integrally formed with said cuvette. [The present invention 1118] The method of claim 1112, wherein the aberration correction plate is spaced from the cuvette. [The present invention 1119] The method of claim 1102, wherein the observation zone is inside the jet stream. [The present invention 1120] 1119. The method of claim 1119, wherein the concave mirror is a surface mirror. [The present invention 1121] The method of claim 1102, wherein said observation zone is disposed on a surface of a flat transparent substrate. [The present invention 1122] The method of claim 1121, wherein the concave mirror is a plano-concave back-surface mirror made from an optically transparent material. [The present invention 1123] The method of claim 1122, wherein a planar surface of said plano-concave back-surface mirror means is optically coupled to said flat transparent substrate. [The present invention 1124] The method of claim 1123, wherein an optical adhesive material provides said optical bond. [The present invention 1125] The method of claim 1123, wherein a refractive index matching gel provides said optical coupling. [The present invention 1126] The method of claim 1123, wherein an index matching fluid provides said optical coupling. [The present invention 1127] The method of claim 1123, wherein an optical contact bond provides said optical coupling. [The present invention 1128] The method of claim 1122, wherein said plano-concave back-surface mirror is integrally formed with said flat transparent substrate. [The present invention 1129] The method of claim 1128, wherein the aberration correction plate is spaced from the flat transparent substrate. [The present invention 1130] A fluid subsystem (70) for providing a pulse-free liquid flow to an outlet of the fluid subsystem (70), comprising: (a) a liquid pump for supplying liquid drawn from a reservoir; (b) A T-shaped connector having at least one inlet and two outlets, i. the inlet of the T-connector receives liquid from the liquid pump; ii. a first portion of the liquid received by the inlet flows through a first one of the outlets and a bypass conduit back to the reservoir; and iii. a second portion of the liquid received by the inlet flows through a second one of the outlets and a particulate filter to the outlet of a fluid subsystem (70); A T-shaped connector, a fluid subsystem (70). [The present invention 1131] A fluid subsystem (70) of the present invention 1130, wherein the particulate filter has an inlet for receiving liquid from the T-junction, and the inlet of the particulate filter is positioned such that air is trapped within the particulate filter at the inlet. [The present invention 1132] The fluid subsystem (70) of the present invention 1131, wherein air cannot enter the bypass conduit when the liquid pump is stopped. [The present invention 1133] The fluid subsystem (70) of the present invention 1132 further comprising a small capsule disposed between a second of the outlets of the T-connector and the particulate filter for storing air expelled from the particulate filter when the liquid pump is stopped. [The present invention 1134] The fluid subsystem (70) of the present invention 1132 further including a length of tubing disposed between a second of the outlets of the T-connector and the particulate filter for storing air exhausted from the particulate filter when the liquid pump is stopped. [This invention 1135] The fluid subsystem (70) of the present invention 1132 further comprising a regulating valve disposed in the bypass conduit between a first of the outlets of the T-connector and the reservoir to restrict liquid flow between the first outlet and the reservoir. [The present invention 1136] The fluid subsystem (70) of the present invention 1132 further comprising an adjusting valve disposed between a second of the outlets of the T-connector and the outlet of the fluid subsystem (70) to restrict liquid flow between the second of the outlets and the outlet of the fluid subsystem (70). [This invention 1137] The fluid subsystem (70) of the present invention 1132, wherein the throughput of the liquid pump is adjustable. [The present invention 1138] 1. A method for providing a pulse-free liquid flow to an outlet of a fluid subsystem (70), comprising: (a) a liquid pump for supplying liquid drawn from a reservoir; (b) A T-shaped connector having at least one inlet and two outlets, i. the inlet of the T-connector receives liquid from the liquid pump; ii. a first portion of the liquid received by the inlet flows through a first one of the outlets and a bypass conduit back to the reservoir; and iii. a second portion of the liquid received by the inlet flows through a second one of the outlets and a particulate filter to the outlet of a fluid subsystem (70); A T-shaped connector, A method comprising: [The present invention 1139] The method of claim 1138, wherein during normal operation, a volume of air is trapped adjacent the inlet portion of said filter cartridge means. [The present invention 1140] 1139. A method according to claim 1139, wherein said reservoir means holds a sufficient amount of liquid to prevent said trapped air from leaking into said bypass means such that a portion of the tube between said T-shaped means and said reservoir means is still filled with liquid when said pump means is stopped. [This invention 1141] The method of claim 1140, wherein said reservoir means is a capsule. [This invention 1142] The method of claim 1140, wherein said reservoir means is a portion of a tube. [This invention 1143] The method of any one of claims 1140 to 1150, wherein an adjustable flow restrictor means is disposed in said bypass path. [This invention 1144] The method of the present invention 1140, wherein an adjustable flow restrictor means is disposed within the sheath passageway. [This invention 1145] The method of any one of claims 1140 to 1150, wherein the throughput of said sheath pump is adjustable. [This invention 1146] (a) a pump housing having an arcuate curved track formed therein, the arcuate curved track extending between a pump inlet and a pump outlet; (b) a plurality of rollers attached to a rotor, the rollers having substantially equal angular spacing between each immediately adjacent pair of rollers, the rotor being rotatable with the rollers attached to the rotor inside the pump housing; and (c) a compressible tube sandwiched between the roller and the arcuate track of the pump housing, the arcuate track comprising: i. an outlet section, wherein as a roller rolls through said outlet section, said compressible tube adjacent said roller continuously expands from a fully closed condition at the beginning of said outlet section to a fully open condition at said pump outlet where said roller loses contact with said compressible tube; ii. at least one pump section along said arcuate track between said pump inlet and said pump outlet, said compressible tube being compressed to a fully closed condition by at least one of said rollers; a compressible tube comprising: a peristaltic pump 80 including [Invention 1147] A peristaltic pump 80 of the present invention 1146, wherein the arcuate track of the pump housing includes at least two pump sections, and the arcuate track further includes at least one recessed portion disposed between the pump sections along the arcuate track, and when one of the rollers rolls through the recessed portion, the compressible tube in the recessed portion is decompressed to a fully expanded state and then compressed to a fully closed state. [This invention 1148] A peristaltic pump 80 of the present invention 1147 including a plurality of recessed portions along the arcuate track upstream of the pump outlet, wherein the angular spacing between the compressed portion of the recessed portion adjacent the pump outlet and the outlet portion of the arcuate track is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [This invention 1149] A peristaltic pump 80 of the present invention 1147, wherein the compressed portion of the recessed portion adjacent the pump outlet has a shape complementary to the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the total fluid volume within the portion of the compressible tube extending from the recessed portion to the pump outlet is maintained substantially constant. [The present invention 1150] A peristaltic pump 80 of the present invention 1147 having a plurality of recessed portions each interspersed between immediately adjacent pairs of a plurality of pump portions. [This invention 1151] (a) the angular spacing between adjacent pairs of recessed portions; (b) an angular spacing between the exit portion of the arcuate track and a recessed portion adjacent the exit portion; and is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [This invention 1152] A peristaltic pump 80 of the present invention 1150, wherein the shape of the multiple recessed portions of the arcuate track complements the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the fluid volume within the multiple recessed portions and the portion of the compressible tube at the outlet portion remains substantially constant. [This invention 1153] A peristaltic pump 80 of the present invention 1146, wherein the speed of the rotor is programmably controlled to vary substantially inversely proportional to the rate of change of fluid volume in the compressible tube due to changes in compression of the compressible tube near the outlet portion of the arcuate track. [This invention 1154] 1. A method for delivering a liquid using a peristaltic pump 80 comprising: (a) a pump housing having an arcuate curved track; (b) a plurality of rollers attached to rotor means rotatable inside said pump housing; and (c) the rollers being spaced from one another at substantially equal angular intervals; and (d) a compressible tube sandwiched between the roller and the arcuate track of the pump housing; (e) the arcuate track of the pump housing including an outlet portion, wherein the compressible tube is continuously depressurized to full expansion when one of the rollers rolls off the compressible tube at the pump outlet; and (f) at least one pump section along the arcuate track of the pump housing between a pump inlet and a pump outlet, wherein the compressible tube is compressed to full closure by one of the rollers. [This invention 1155] The method of claim 1154, wherein the arcuate track of the pump housing includes at least two pump sections, the arcuate track further includes at least one recessed portion disposed between the pump sections along the arcuate track, and when one of the rollers rolls through the recessed portion, the compressible tube in the recessed portion is decompressed to a fully expanded state and then compressed to a fully closed state. [This invention 1156] The method of the present invention 1155, wherein the peristaltic pump 80 includes a plurality of recessed portions along the arcuate track upstream of the pump outlet, and the angular spacing between the compressed portion of the recessed portion adjacent the pump outlet and the outlet portion of the arcuate track is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [This invention 1157] The method of claim 1155, wherein the compressed portion of the recessed portion adjacent the pump outlet has a shape complementary to the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the total fluid volume inside the portion of the compressible tube extending from the recessed portion to the pump outlet remains substantially unchanged. [This invention 1158] The method of the present invention 1155, having a plurality of recessed portions each interspersed between immediately adjacent pairs of the plurality of pump portions. [This invention 1159] (a) the angular spacing between adjacent pairs of recessed portions; (b) an angular spacing between the exit portion of the arcuate track and a recessed portion adjacent the exit portion; and is substantially the same as the angular spacing between each immediately adjacent pair of rollers. [The present invention 1160] The method of claim 1158, wherein the shape of the plurality of recessed portions of the arcuate track complements the shape of the outlet portion of the arcuate track, and when one of the rollers continuously rolls away from the outlet portion of the arcuate track, the fluid volume within the plurality of recessed portions and the portion of the compressible tube at the outlet portion is maintained substantially constant. [The present invention 1161] The method of the present invention 1154, wherein the speed of the rotor of peristaltic pump 80 is programmably controlled to vary substantially inversely proportional to the rate of change of fluid volume in the compressible tube due to changes in compression of the compressible tube near the outlet portion of the arcuate track. [The present invention 1162] a WDM (90) for splitting the emitted light beam into a plurality of color bands, (a) a collimating optic that magnifies the image to produce an image substantially the same size as the effective size of the collimating optic; (b) at least one dichroic filter disposed between the collimating optics and the image, the at least one dichroic filter separating the collimated light beam into two characteristic color branches; (c) a focusing optic disposed within one of the branches, the focusing optic causing the light beam within the branch to be focused to a spot having a diameter of less than 1.0 mm; (d) an image relay optical element disposed in the other branch adjacent to an image generated by the collimating optical element, the image relay optical element generating an image of the collimating optical element at substantially the same magnification; Including, WDM(90). [The present invention 1163] A WDM (90) of the present invention 1162, wherein at least one additional dichroic filter is disposed between the image relay optical element and the image produced by the image relay optical element, the dichroic filter generating two branches of the light beam having characteristic colors. [The present invention 1164] The WDM (90) of the present invention 1163, wherein another focusing optical element is disposed within one of the branches to focus the light beam within the branch to a spot having a diameter of less than 1.0 mm. [The present invention 1165] The WDM (90) of the present invention 1164, wherein the successive combination of image relay optics, dichroic filters, and focusing optics are cascaded to generate additional focused spots having diameters of less than 1.0 mm for multiple color bands of the light beam. [The present invention 1166] A WDM (90) of the present invention 1164, wherein the dichroic filter is assembled using a template including two optically flat glass plates bonded together in optical contact, and the template is used to bond the dichroic filter to a filter holder, such that a coated filter surface of the dichroic filter is recessed relative to a reference plane of the filter holder and optically parallel to the reference plane. [The present invention 1167] A WDM (90) of the present invention 1166, wherein the reference surface of the filter holder rests against an optically flat surface of a reference block contained within the WDM (90), thereby providing consistent optical alignment when installing the dichroic filter within the WDM (90). [The present invention 1168] A method for separating an emitted light beam into color bands using a WDM (90) comprising: (a) a collimating optic that magnifies the image to produce an image substantially the same size as the effective size of the collimating optic; (b) at least one dichroic filter disposed between the collimating optics and the image, the at least one dichroic filter separating the collimated light beam into two characteristic color branches; and (c) a focusing optic disposed within one of the branches, the focusing optic causing the light beam within the branch to be focused to a spot having a diameter of less than 1.0 mm; (d) an image relay optical element disposed adjacent to the image produced by the collimating optical element in the other branch, the image relay optical element producing an image of the collimating optical element at substantially the same magnification; [The present invention 1169] The method of claim 1168, wherein at least one additional dichroic filter is disposed between the image relay optical element and the image produced by the image relay optical element, the dichroic filter generating two branches of the light beam having characteristic colors. [The present invention 1170] The method of claim 1169, wherein another focusing optical element is disposed within one of said branches to focus said light beam within said branch to a spot having a diameter of less than 1.0 mm. [This invention 1171] The method of claim 1170, wherein the successive combination of image relay optics, dichroic filters, and focusing optics are cascaded to generate additional focused spots having diameters of less than 1.0 mm for multiple color bands of the light beam. [This invention 1172] The method of claim 1170, wherein the dichroic filter is assembled using a template including two optically flat glass plates bonded together in optical contact, and the dichroic filter is bonded to a filter holder using the template, such that a coated filter surface of the dichroic filter is recessed relative to a reference surface of the filter holder and optically parallel to the reference surface. [This invention 1173] A method of the present invention 1172, wherein the reference surface of the filter holder is supported against an optically flat surface of a reference block contained within a WDM (90), thereby providing consistent optical alignment when installing the dichroic filter within a WDM (90). These and other features, objects and advantages will be clearly understood by those skilled in the art from the various drawings and the following detailed description of preferred embodiments of the present disclosure. [Brief description of the drawings]

[0043] [Figure 1]FIG. 13 is a schematic diagram illustrating a preferred embodiment of a flow cytometer according to the present disclosure, including: (a) an LD-based optical illumination subsystem; (b) a compound microscope objective into which light emitted from the LD-based optical illumination subsystem is incident, the compound microscope objective having a fluid-through channel formed therein with a particle illumination observation zone disposed inside the cuvette; (c) a fluidic system for supplying a pulsation-free sheath liquid flow to the fluid-through channel formed in the compound microscope objective; (d) a peristaltic pump for introducing a pulsation-free sample liquid flow carrying cells or particles to be analyzed into the sheath liquid flow supplied by the fluidic system; and (e) a wavelength division multiplexer ("WDM") having a zigzag configuration for separating a light beam into several different color bands, the WDM receiving, via an optical fiber, light scattered from the cells or particles when the cells or particles pass through the fluid-through channel of the compound microscope objective and are illuminated therein by light emitted from the LD-based optical illumination subsystem. [Diagram 2] FIG. 1 is a schematic diagram of a typical high-power edge-emitting LD, showing the fast and slow axes of light emitted from the LD. [Figure 2A] 3 shows a typical far-field profile for a laser beam emitted from the LD chip shown in FIG. [Figure 3A] FIG. 1 shows a three-dimensional representation of a conventional prior art LD-based optical illumination subsystem for a flow cytometry instrument along with the system's flow cell. [Figure 3B] FIG. 3B shows a typical time-dependent profile of light scattered from a cell or particle passing through the laser beam shown in FIG. 3A at a focal point within the flow cell of the system. [Figure 4A] FIG. 1 is an elevational view, across liquid flowing through a fluid-through channel, of another prior art LD-based optical illumination subsystem configuration that improves the beam profile at a focal point within the observation zone of a flow cytometer system. [Figure 4B]FIG. 4B is a plan view along the liquid flowing through the fluid-through channels of another prior art LD-based optical illumination subsystem shown in FIG. 4A. [Diagram 5] Figure 5A is an elevational view across the liquid flowing through the fluid-through channel of the compound microscope objective shown in Figure 1, with the slow axis of the LD oriented transverse to the liquid flow. Figure 5B is a plan view along the liquid flowing through the fluid-through channel of the compound microscope objective shown in Figure 1, with the slow axis of the LD oriented transverse to the liquid flow. Figure 5C shows a typical time-dependent profile of light scattered from a cell or particle passing through the fluid-through channel of the compound microscope objective shown in Figure 1. [Figure 6] FIG. 13 is a perspective view of another embodiment of an LD-based optical illumination subsystem according to the present disclosure adapted for use in a flow cytometer system in which a jet stream of liquid passes through an observation zone. [Figure 6A] FIG. 13 is an enlarged perspective view of another embodiment of an LD-based optical illumination subsystem showing in more detail the jet of liquid passing through the observation zone. [Figure 7] FIG. 2 is a perspective view of another embodiment of an LD-based optical illumination subsystem according to the present disclosure adapted for use in a flow cytometer system in which the slow axis of the LD is oriented parallel to the direction of liquid flowing through the fluid-through channel of the compound microscope objective shown in FIG. [Figure 8] FIG. 2 is a perspective view of a compound microscope objective according to the present disclosure adapted for use in the flow cytometer system shown in FIG. 1, the compound microscope objective having a fluid-passing flow path formed therein and a particle illumination observation zone disposed inside the cuvette. [Figure 9A] 9A is an elevational cross-sectional view of a compound microscope objective taken along line 9A-9A in FIG. 8, including ray traces from three spatially separated locations within the observation zone to the image plane of the objective, showing the propagation of scattered light and fluorescent light. [Figure 9B]9B is a diagram of spots near the image plane shown in FIG. 9A for the three spatially separated light emission positions shown in FIG. 9A. [Figure 10] FIG. 9B is a cross-sectional elevation view similar to FIG. 9A of another embodiment of a compound microscope objective according to the present disclosure, including ray traces from three spatially separated locations within the observation zone to the image plane of the objective, showing the propagation of scattered light and fluorescent light. [Figure 11] FIG. 2 is a perspective view of yet another alternative embodiment of a compound microscope objective lens according to the present disclosure adapted for use with the flow cytometer system shown in FIG. 1, the alternative embodiment of the compound microscope objective lens having a fluid-passing flow path formed therein and a particle illumination observation zone disposed inside the cuvette. [Figure 12] FIG. 2 is a perspective view of yet another alternative embodiment of a compound microscope objective lens according to the present disclosure adapted for use in the flow cytometer system shown in FIG. 1, the alternative embodiment of the compound microscope objective lens being adapted for an observation zone located inside the jet stream shown in FIGS. 6 and 6A. [Figure 13] FIG. 13 is a perspective view of yet another alternative embodiment of a compound microscope objective according to the present disclosure adapted for use, with an observation zone disposed on a surface of a microscope slide. [Figure 14] FIG. 1 is a schematic diagram of a fluidic subsystem according to the present disclosure for providing a stable flow of sheath fluid to a flow cytometer flow cell, the fluidic subsystem including: 1. a small capsule positioned between the sheath fluid pump and the flow cell; and 2. a particle filter positioned between the small capsule and the flow cell, the particle filter and the small capsule together providing an air reservoir for damping pump pulsations. [Figure 15] FIG. 15 is a schematic diagram of an alternative embodiment of a fluid subsystem similar to that shown in FIG. 14, in which the small capsule is replaced with a length of tubing to provide an air reservoir. [Figure 16]16A-B are histograms comparing particle flight times measured in a flow cell when the inlet portion of the particle filter has air trapped inside (FIG. 16A) and when there is no air in the fluidic subsystem between the sheath liquid pump and the flow cell (FIG. 16B). [Figure 17] FIG. 1 is a perspective view of a three-roller peristaltic pump according to the present disclosure, showing the pump's rollers, tubing, and surrounding pump housing. [Figure 18] 18A-18C are simplified diagrams illustrating several states of the three-roller peristaltic pump shown in FIG. 17 with the rollers in different positions. [Figure 19] FIG. 1 is a longitudinal cross-sectional detail of a peristaltic pump tube being partially compressed by the pump rollers. [Figure 19-1] 19A and 19B are cross-sectional views of the peristaltic pump taken along lines 19A and 19B in FIG. 19, showing in detail the partial compression of the tube by the rollers perpendicular to the length of the tube. [Figure 20] FIG. 13 is a schematic diagram of the pump rollers and tubing as viewed along the pump's circular coordinate system illustrating the absence of pulsation caused by a peristaltic pump. [Figure 21] Graph showing 1. total liquid volume in the outlet half of the pump, and 2. liquid volume in a. recessed portion and b. outlet portion of the pump as a function of roller position as it rolls off the outlet portion of the compressible tube. [Figure 22] FIG. 1 is a simplified plan view of a four-roller peristaltic pump according to the present disclosure. [Diagram 23] FIG. 1 is a simplified plan view of a six-roller peristaltic pump according to the present disclosure. [Figure 24]FIGURE 24A is a longitudinal section view of the rollers and compressible tubing for a pulsation-minimizing three roller peristaltic pump with a rotor with programmable speed according to the present disclosure. FIGURE 24B is a simplified plan view of a pulsation-minimizing three roller peristaltic pump with a rotor with programmable speed according to the present disclosure. FIGURE 24C is a graph showing the pulsation-minimizing peristaltic pump shown in FIGURE 24B with programmable rotor speed according to the present disclosure: 1. Negative volume change rate versus roller position, 2. rotor speed, and 3. pump flow rate. [Diagram 25] FIG. 1 illustrates optical ray tracing of an exemplary 6-port wavelength division multiplexer ("WDM") using a zigzag configuration in accordance with the present disclosure. [Figure 26] FIG. 1 shows ray tracings of a prior art collimating device illustrating the limitations of the device in collimating a distributed light source. [Figure 27] FIG. 1 is a perspective view of an embodiment of a 6-port WDM using a combination of a zigzag configuration and a branching configuration in accordance with the present disclosure. [Figure 28] FIG. 1 is a perspective view of another embodiment of a WDM having a concave dichroic filter according to the present disclosure. [Figure 29] 29A and 29B are perspective views illustrating an assembly process for constructing an interchangeable dichroic filter assembly for a reconfigurable WDM according to the present disclosure, and FIG 29C is a perspective view of an interchangeable dichroic filter assembly constructed according to FIG 29A and 29B. [Diagram 30] 29D is a perspective view of a WDM according to the present disclosure illustrating the installation and removal of the replaceable dichroic filter assembly shown in FIG. 29C into the WDM. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] BEST MODE FOR CARRYING OUT THE DISCLOSURE Flow cytometer FIG. 1 illustrates a flow cytometer according to the present disclosure, identified by the general reference character 40. Flow cytometer 40 includes: 1. An LD-based optical subsystem 50; 2. A compound microscope objective 60; and 3. A fluidic subsystem 70 for providing a sheath fluid flow; 4. A peristaltic pump 80 for injecting a sample liquid flow containing the particles to be analyzed into the sheath liquid flow provided by the fluidic subsystem 70, the sample liquid flow being hydrodynamically constricted by the sheath liquid flow passing through an observation zone where the compound microscope objective 60 collects and images the light scattered by the particles and / or the fluorescence emitted by said particles; 5. An optical fiber 852 for receiving light scattered by and / or fluorescent light emitted by particles in the observation zone, which is collected and imaged by the compound microscope objective 60; 6. A wavelength division multiplexer 90 ("WDM 90") for optically processing the scattered light and / or fluorescent light received from the optical fiber 852; Includes.

[0045] Optical Subsystem 50 The optical subsystem 50 includes a LD 501 that emits a diverging light beam from an end face of the LD, as shown in more detail in FIG. 2. As shown more visually in FIG. 2 and FIG. 2A, the diverging light beam has an elliptical cross-sectional profile with both a major axis, also called a fast axis, and a minor axis, also called a slow axis. The diverging light beam emitted from the LD 501 is incident on a collimating lens 502, which converts the diverging light beam emitted by the LD 501 into a collimated light beam with an elliptical cross-section. Although not required, the optical subsystem 50 includes an optional mirror 503 positioned to direct the collimated elliptical light beam toward the compound microscope objective 60. A plano-convex lens 504 positioned near the compound microscope objective 60 reduces the major axis of the elliptical light beam, which is oriented perpendicular to the direction in which the sample liquid and the surrounding sheath liquid flow through the observation zone within the compound microscope objective 60. In the observation zone, the width of the elliptical light beam is 1. The width perpendicular to the direction in which the sample liquid flow passes through the observation zone is preferably slightly shorter than the width of the sheath liquid flow, while 2. Still wide enough that particles within the sample liquid flow pass through the nearly flat portion of the elliptical light beam at the beam's maximum intensity.

[0046] It will be apparent to those skilled in the art that, according to the present disclosure, plano-convex lens 504 can be replaced with other types of optical elements, such as an achromatic lens, or a combination of spherical lenses, cylindrical lenses, and / or prism pairs. Alternatively, mirror 503 and lens 504 can also be replaced with concave mirrors. For polarization-sensitive applications of flow cytometer 40, an optional polarization adjusting element, such as a half-wave plate, can also be placed within the collimated portion of the light beam extending from collimating lens 502 to lens 504. Finally, before passing through the observation zone, the light beam passes through a high-magnification cylindrical lens 505 positioned adjacent to the observation zone. As shown in FIG. 1, the axis of cylindrical lens 505 is oriented perpendicular to the direction of sample liquid flow through the observation zone, and the focal length of cylindrical lens 505 results in tight focusing of the short axis of the light beam at the observation zone.

[0047] The advantages of the optical subsystem 50 compared to a conventional LD-based optical subsystem are more clearly illustrated in Figures 2 and 2A. Most commercially available laser diodes suitable for use in flow cytometers emit a light beam from the laser diode end facet. As shown in Figure 2, the gain section 509 of such a LD chip 510 is highly confined in the transverse direction indicated by arrow 511. This often leads LD manufacturers to sacrifice beam quality, particularly along the transverse or fast axis direction, which is oriented parallel to arrow 511, in order to achieve high power output. Figure 2A illustrates the characteristics of light emitted from a LD, where multiple interference fringes 512 resulting from gain confinement are clearly visible in the far field along the short axis of the emitted light beam. The interference fringes 512 seen in the diagram of Figure 2A contain only a small amount of the total energy of the light beam and therefore are much smaller than the conventional M of the corresponding beam profile. 2 Note that this has little effect on the characterization. However, as explained in more detail below, the interference fringes 512 adversely affect the performance of conventional flow cytometers. Alternatively, the gain confinement along the slow axis direction of the edge-emitting LD, which is oriented perpendicular to the arrow 511, is much looser. This results in a smoother far-field beam profile along the slow axis of the LD's light beam, as shown in FIG. 2A.

[0048] FIG. 3A shows a conventional LD-based optical subsystem for a flow cytometer. Those elements shown in FIG. 3A that are common to the optical subsystem 50 shown in FIG. 1 are labeled with the same reference numerals, distinguished by a prime (') symbol. As shown in FIG. 3A, the conventional optical subsystem orients the fast axis of the LD 501 parallel to the direction in which the sample liquid flow passes through the observation zone. In its simplest configuration, the elliptical beam profile of the LD 501' is directly transposed into the observation zone by a spherical focusing lens 504'. In an attempt to achieve an optimal aspect ratio for the focused light beam, various different conventional LD-based optical subsystems also include beam shaping optical elements in addition to those shown in FIG. 3A.

[0049] The adverse effect of the interference fringes 512 along the fast axis of the LD 501' for the conventional optical subsystem configuration is clearly visible in the time profile of light scattering shown in FIG. 3B. Since the scattered light intensity or fluorescence intensity is directly proportional to the local laser power incident on the particle, any fine structure in the profile of the light beam along the direction of the sample liquid flow through the observation zone will appear in the time profile of the signal generated by the flow cytometer. Such structures in the time profile cannot be distinguished from the signal generated by small particles, and therefore will falsely trip the flow cytometer and misidentify the particle. Moreover, the interference fringes 512 also cause inaccurate measurements of other cytometric parameters such as the area and width of the pulsation shown in FIG. 3B.

[0050] 4A and 4B show yet another prior art optical subsystem for LD-based flow cytometry applications disclosed in the previously referenced '019 patent. Those elements shown in FIGS. 4A and 4B that are common to the optical subsystem 50 shown in either FIG. 1 or FIG. 3A are labeled with the same reference numerals, differentiated by a double prime ('') symbol. As shown in FIGS. 4A and 4B, by orienting the slow axis of the LD 501'' parallel to the direction of sample liquid flow through the observation zone, the optical subsystem shown in FIGS. 4A and 4B effectively overcomes the problem caused by the interference fringes 512 as described above. Unfortunately, the beam spreading element 513'' placed in front of the spherical focusing lens 504'' in FIGS. 4A and 4B to spread the light beam perpendicular to the direction of sample liquid flow through the observation zone creates a highly astigmatic light beam near the observation zone. Specifically, by focusing this astigmatic light beam in the observation zone in the direction of the sample liquid flow through the observation zone, the width of the light beam perpendicular to the direction of the sample liquid flow through the observation zone is increased so that the width of the beam is the same as or even wider than the sheath flow. Thus, the optical subsystem shown in Figures 4A and 4b not only reduces the amount of light energy incident on particles flowing through the observation zone, but the optical subsystem also increases undesirable scattered light from the interface between the sheath liquid flow and adjacent portions of the compound microscope objective lens 60.

[0051] FIG. 5 highlights the main differences between the optical subsystem disclosed in the '019 patent and the optical subsystem 50 shown in FIG. 1. Instead of placing an out-of-plane beam spreading element 513" in front of the spherical beam focusing lens 504 as shown in FIG. 4, a high magnification cylindrical lens 505, shown in FIGS. 5A and 5B as a cylindrical plano-convex lens, is placed in line with the light beam after the spherical beam focusing lens 504, preferably juxtaposed with the compound microscope objective lens 60. As shown in FIGS. 5A and 5B, the cylindrical lens 505 focuses the short axis of the light beam within the observation zone, while the long axis of the light beam remains essentially unchanged. This allows the optical subsystem 50 shown in FIGS. 1, 5A and 5B to: 1. A tightly focused short axis spanning the combined sample and sheath liquid flows; 2. A smooth short-axis profile in the direction of the combined sample and sheath liquid flows, which is the Fourier conjugate of the far-field beam profile along the slow axis of the LD501; A light beam profile is established in the observation zone that is an ellipse having

[0052] On the other hand, as shown in Figure 5B, the out-of-plane beam width is not affected by the cylindrical lens 505. Figure 5C shows the measured temporal profile of light scattered from a particulate using the optical subsystem 50 shown in Figures 1, 5A and 5B. The LD 501 used in making the measurement presented in Figure 5C is the same as that used in creating the measured temporal profile of light scattered from a particulate represented in Figure 3B. As shown in Figure 5C, the side lobes caused by the interference fringes 512 along the fast axis of the LD 501 no longer significantly affect the performance of the flow cytometer 40.

[0053] FIG. 6 illustrates yet another alternative diode laser-based optical subsystem according to the present disclosure adapted for use in a flow cytometer. Those elements illustrated in FIGS. 6 and 6A that are common to the optical subsystem 50 illustrated in FIGS. 1, 5A, and 5B are labeled with the same reference numerals, distinguished by a triple prime (''') symbol. The optical subsystem 50''' illustrated in FIGS. 6A and 6B is substantially the same as that illustrated in FIGS. 1, 5A, and 5B, except that the observation zone occurs without the use of a compound microscope objective lens 60, since the observation zone occurs within a free-flowing jet stream 519 that includes both sample and sheath flows emitted from a nozzle 518. This allows the high magnification cylindrical lens 505 to be spaced apart from the observation zone, which is located within the jet stream 519, in the configuration of the optical subsystem 50''' illustrated in FIGS. 6A and 6B.

[0054] In the exemplary embodiment of the present disclosure shown in Figures 1, 5A, 5B, 6A and 6B, the short or slow axis of LD 501 is oriented perpendicular to the direction of sample liquid flow through the observation zone. However, it will be clear to one of ordinary skill in the art that other optical configurations can be used to orient the long or fast axis of LD 501 to be perpendicular to the direction of sample liquid flow through the observation zone. Figure 7 shows an example of another configuration of such optical elements. Those elements shown in Figure 7 that are common to the optical subsystem 50 shown in Figures 1, 5A, 5B, 6A and 6B are numbered the same, differentiated by a four prime ('''') symbol. As shown, the slow axis of LD 501'''' is oriented in the z direction. The light beam emitted from LD 501'''' is then rotated into the y plane by a pair of 90° mirrors 523a and 523b. In FIG. 7, the normal to the mirror 523a that redirects the first elliptical light beam is oriented in the xy plane at 45° to the x-axis, and the normal to the mirror 523b that redirects the second elliptical light beam is oriented in the yz plane at 45° to the z-axis.

[0055] Compound Microscope Objective Lens 60 FIG. 8 illustrates the compound microscope objective 60 shown in FIGS. 1, 5A, 5B, and 7 according to one embodiment of the present disclosure. As illustrated in FIG. 8, the compound microscope objective 60 images an observation zone disposed inside a prism-shaped glass cuvette 603 in a minor flow channel 604, preferably having a rectangular cross-sectional shape through which the combined particle-carrying sample and sheath liquid flows pass. A plano-concave back-surface mirror 601 included in the compound microscope objective 60 is made from an optically transparent material, such as glass or optical quality plastic, preferably having a similar refractive index as the glass cuvette 603. To minimize optical losses, the back-surface mirror 601 includes a flat front surface optically coupled to the abutment plane of the prism-shaped cuvette 603. The optical coupling of the back-surface mirror 601 to the cuvette 603 may use a refractive index matching gel, an optical adhesive, or a direct optical bond. Alternatively, the back-surface mirror 601 may be integrally formed with the cuvette 603.

[0056] Compound microscope objective 60 also includes a flat aspheric correction plate 602 made from an optically transparent material, such as glass or optical quality plastic, preferably having a similar refractive index as glass cuvette 603. To reduce optical losses, the flat surface of correction plate 602 is optically coupled to the abutting flat surface of prism-shaped cuvette 603 on the side of prism-shaped cuvette 603 diametrically opposite back-surface mirror 601. Optical coupling of correction plate 602 to cuvette 603 may use index-matching gel, optical adhesive, or direct optical bonding. The aspheric surface of correction plate 602 most distal from correction plate 602 may have an anti-reflective coating to reduce losses in light transmission, although such a coating is not a requirement for compound microscope objective 60 according to the present disclosure. The aspheric shape of correction plate 602 is similar to the classical Schmidt camera (Schmidt, B., Mitt. Hamburg Sternwart 7 (36) 1932). As known to those skilled in the art, the compensation plate of a Schmidt camera includes a circular intermediate zone where the compensation plate does not deflect the light rays passing through the plate. When used in a compound microscope objective 60, outside the intermediate zone of the compensation plate 602 where the plate thickness is thinnest, the compensation plate 602 has a negative optical power, while inside the intermediate zone, the compensation plate 602 has a positive optical power. The exact shape of the aspheric compensation plate 602 can be easily obtained by those skilled in the art using any commercially available optical ray tracing tool. It should be noted that in the flow cytometer 40, the light beam generated by the optical subsystem 50 shown in FIGS. 1, 5A, 5B and 7 enters the cuvette 603 perpendicular to the flow channel 604 through one of the two faces of the cuvette 603 that does not abut either the back-surface mirror 601 or the compensation plate 602.

[0057] Figure 9A shows ray tracing results for the embodiment of compound microscope objective 60 shown in Figure 8. As shown in Figure 9A, the scattering and fluorescence emissions from three spatially separated locations in flow channel 604 near the center of cuvette 603 are 1. First, it propagates towards the back-coated mirror 601 and is internally reflected by the back-coated mirror 601, 2. Next, first pass through cuvette 603, 3. It then passes through the aspheric correction plate 602, 4. Finally, form three different images near the image plane 605.

[0058] 9A is nearly optically uniform, and light emitted near the center of the cuvette 603 intersects the correction plate 602 at nearly normal incidence. This causes the compound microscope objective 60 to introduce little chromatic dispersion into the light emitted near the center of the cuvette 603.

[0059] Moreover, it is well known in the astrophysics world that Schmidt cameras offer an unparalleled combination of bright focal ratio and wide field of view with nearly diffraction-limited optical performance. The main drawback of conventional Schmidt cameras is that the image plane is inside the instrument. With the compound microscope objective 60, light near the center of the cuvette 603 propagates in the opposite direction to conventional Schmidt cameras, and therefore the image plane is outside the compound microscope objective 60. This allows the present disclosure to fully utilize only the advantages of the optical performance of Schmidt cameras without being limited by conventional Schmidt cameras. Figures 9B1-9B3 show spot diagrams near the image plane 605 for three emission positions in the observation zone in the flow channel 604, which are spaced 150 microns apart from each other. The diameters of all images shown in Figures 9B1-9B3 are below 35 microns.

[0060] Light emitted from the observation zone in the flow channel 604 of the compound microscope objective 60 shown in Figures 8 and 9A that traverses the aspheric corrector plate 602 experiences a small amount of chromatic aberration. Figure 10 shows an alternative embodiment for the compound microscope objective 60 shown in Figures 1, 5A, 5B, and 7. Those elements shown in Figure 10 that are common to the compound microscope objective 60 shown in Figures 8 and 9A are given the same reference numerals, differentiated by a prime (') symbol. The geometry of the back-surface mirror 601' and the aberration corrector plate 602' shown in Figure 10 has been slightly modified to produce a collimated afocal image of the emission location near the observation zone in the flow channel 604'. In Figure 10, the compound microscope objective 60' also includes a chromatically corrected doublet lens 609 inserted between the corrector plate 602' and the image plane 605'. In addition to focusing the light emitted from the corrector 602' to the image plane 605', the doublet lens 609 also serves to further reduce the residual chromatic aberration caused by the aspheric corrector 602'.

[0061] The flat surface of the correction plate 602 does not necessarily have to be optically coupled to the cuvette 603. FIG. 11 illustrates a compound microscope objective 60 according to an alternative embodiment of the present disclosure. Those elements illustrated in FIG. 11 that are common to the compound microscope objective 60 illustrated in FIGS. 8 and 9A are labeled with the same reference numerals, differentiated by a double prime ('') symbol. FIG. 11 illustrates an aberration correction plate 602'' that is optically separated from the cuvette 603''. Although not essential to the operation of the compound microscope objective 60'', both sides of the aberration correction plate 602'' and the exposed flat surface of the cuvette 603'' can have an anti-reflective coating to improve light transmission efficiency. It will be understood that the aberration correction plate 602'' illustrated in FIG. 11 is held in fixed relationship to the combined back-surface mirror 601 and cuvette 603 by mechanical supports, not illustrated in FIG. 11. Similar to the compound microscope objective lenses 60 and 60' shown in Figures 9A and 10, respectively, the compound microscope objective lens 60'' with a separate corrector plate 602'' can be configured to provide either a finite focal length image, or, by adding a chromatically corrected doublet lens 609, an afocal system which is now focused to a finite distance image plane.

[0062] FIG. 12 illustrates a compound microscope objective 60 according to yet another alternative embodiment of the present disclosure. Those elements illustrated in FIG. 12 that are common to the compound microscope objective 60 illustrated in FIGS. 8, 9A, and 11 are labeled with the same reference numerals, distinguished by a triple prime ('''') designation. The compound microscope objective 60'' illustrated in FIG. 12 is adapted to collect scattered and fluorescent emissions from cells or other microscopic particles carried in a jet stream 519 emitted by a nozzle 518. The compound microscope objective 60''' comprises a concave spherical surface mirror 610 and an aberration correction plate 612. The surface mirror 610 can be made from glass or other types of hard materials with a highly reflective coating on the concave surface 611, or from a metal with a polished concave surface 611. Similar to the corrector plate 602, the planar aspheric corrector plate 612 is made from a thin piece of transparent material, such as glass or optical quality plastic. An aspheric surface is formed on either side of the corrector plate 612. Preferably, both sides of the compensation plate 612 are coated with an anti-reflective coating to reduce light transmission losses, although such coatings are not required for the compensation plate 612 according to the present disclosure. It will be appreciated that the first surface mirror 610 and the compensation plate 612 are held in a fixed relationship to one another by mechanical supports, not shown in FIG. 12. Scattered light and fluorescence emitted from cells or other types of microscopic particles within the observation zone inside the jet stream 519 is reflected by the concave surface 611 of the first surface mirror 610. Aberrations due to reflection from the concave surface 611 are corrected by the compensation plate 612 after the light traverses the compensation plate 612. The compound microscope objective 60''' is configured to provide either a finite focal image, similar to that shown in FIG. 9A, or a collimated afocal image focused at a finite distance from the compound microscope objective 60''' by a chromatically corrected doublet lens, similar to the doublet lens 609 shown in FIG. 10.

[0063] FIG. 13 illustrates the adaptation of a compound microscope objective 60 for imaging a specimen affixed to the surface of a transparent substrate such as a glass slide. Those elements illustrated in FIG. 13 that are common to the compound microscope objective 60 illustrated in FIGS. 8, 9A, and 11 are labeled with the same reference numerals, differentiated by a four-prime ('''') symbol. The compound microscope objective 60'''' illustrated in FIG. 13 includes two optical elements: a plano-concave back-surface mirror 617 made of a transparent material such as glass or optical quality plastic, and an aberration correction plate 618. As illustrated in FIG. 13, the specimen to be imaged is affixed to the front surface 615 of a transparent, typically a glass slide 616. The slide 616 is optically coupled to the plane of the back-surface mirror 617, preferably using a thin layer of index-matching fluid. The scattered and fluorescent light emitted by the specimen is reflected by the 1. First, it propagates through the slide 616 and the back-face mirror 617, 2. Internally reflected by the back-surface mirror 617 through the slide 616; 3. Then, through the correction plate 618, 4. Finally, an image is formed at an image plane located above the correction plate 618.

[0064] Fluid Subsystem 70 FIG. 15 illustrates a fluid subsystem 70 according to the present disclosure, including a sheath fluid reservoir 702 and a fluid pump 701 that draws sheath fluid from the sheath fluid reservoir 702. The fluid pump 701 may be a diaphragm pump, or a peristaltic pump, or a piston pump, or any type of continuous fluid pump. The outlet of the fluid pump 701 is connected to the inlet of a T-connector 703 that receives the sheath fluid from the fluid pump 701. The T-connector 703 has two outlets, the first of which is connected to a bypass conduit 710 for returning a portion of the sheath fluid received by the T-connector 703 from the fluid pump 701 back to the sheath fluid reservoir 702. Returning a portion of the sheath fluid received by the T-connector 703 from the fluid pump 701 back to the sheath fluid reservoir 702 is advantageous for two reasons: 1. As shown in FIG. 1, the bypass conduit 710 remains open to the surrounding atmosphere, which effectively dampens the pulsations, thereby significantly reducing the pulsations inherent in the operation of the liquid pump 701. 2. Returning a portion of the sheath fluid received by T-connector 703 from fluid pump 701 to sheath fluid reservoir 702 also effectively reduces the throughput of fluid pump 701, thereby allowing the use of lower cost pumps with relatively higher flow rates in flow cytometer 40.

[0065] The flow resistance of the bypass conduit 710 is denoted as "r" and the flow resistance of the path from the T-junction 703 to the flow channel 604 of the cuvette 603 is denoted as "R". The output resistance to the sheath pump is therefore The result is TIFF0007675791000001.tif11128.

[0066] Because R>>r, the behavior of the fluid pump 701 is dominated by the resistance of the bypass conduit 710, whose hydrodynamic properties are temperature insensitive. Thus, the configuration of the fluidic subsystem 70 shown in Figure 15 also provides a simple mechanism for achieving temperature insensitive sheath fluid flow to the flow channel 604.

[0067] As shown in FIG. 15, the second outlet of the T-connector 703 is preferably connected to the flow path 604 that extends through the cuvette 603, first through a small reservoir capsule 704 and then through a filter cartridge 705. As shown in FIG. 16, an approximately 4-foot long tube 704' is replaced with the small reservoir capsule 704. During the initial stage of the fluidic subsystem 70, some air is trapped in the filter cartridge 705 near its inlet, which is located above the outlet of the filter cartridge 705 as shown in FIG. 15. The air trapped in the filter cartridge 705 acts as an additional fluid capacitor, effectively reducing pulsations in the sheath liquid discharged into the flow path 604 to negligible levels. The large fluid resistance in the flow path 604 causes the air trapped in the filter cartridge 705 to be compressed. When the liquid pump 701 is stopped, the air trapped in the filter cartridge 705 is pushed back towards the T-connector 703, which resembles an exhaust condenser. Even without the small reservoir capsule 704, some of the air expelled from the filter cartridge 705 would reach the bypass conduit 710 due to its low fluid resistance, and when the liquid pump 701 is turned on again, the air would be pushed out of the fluid subsystem 70. Even without an additional air supply, this scenario would be repeated until most of the air is purged from the fluid subsystem 70 and the filter cartridge 705 loses its effectiveness as a pulsation dampener. Thus, the purpose of the small reservoir capsule 704 or conduit 704' is to provide a reservoir to isolate the filter cartridge 705 from the bypass conduit 710, thereby ensuring that any air trapped inside the filter cartridge 705 remains within the fluid subsystem 70 despite repeated start-stop operations of the liquid pump 701.

[0068] The pulsation damping effect of trapped air near the inlet of the filter cartridge 705 is clearly seen in the histograms shown in Figures 16A and 16B. Figure 16A shows particle flight times measured in the flow channel 604 when a pocket of air is trapped near the inlet of the filter cartridge 705. Figure 16B shows particle flight times measured in the flow channel 604 when trapped air is purged from the fluidic subsystem 70. The results shown in the histograms of Figures 16A and 16B are obtained using two knife-edge laser beams focused near the center of the flow channel 604, spaced about 200 μm apart. The horizontal axis of Figures 16A and 16B is the flight time of a particle from one laser beam to the other, measured by recording the time of arrival of the peak of light scattered from the particle at an angle of 90° from the excitation beam. In both cases, the average flight time for a particle to traverse the two laser beams is the same. As shown in Figure 16A, when the filter cartridge 705 holds some air, all particles take approximately the same amount of time to cross the two laser beams. When the filter cartridge 705 does not hold air, as shown in Figure 16B, the distribution of flight times is not only broadened but also bimodal. In other words, some particles take less time, while other particles take longer than the average time to cross the two laser beams. This is a phenomenon that can be easily attributed to pulsations in the sheath liquid velocity in the flow channel 604.

[0069] In the embodiments of the present disclosure described thus far, the flow resistance along the bypass conduit 710 and between the T-junction 703 and the flow channel 604 is not adjustable. As will be apparent to one skilled in the art, flow restrictors such as fixed restrictors or regulator valves 711, 711′ and 712, 712′ may be advantageously inserted in the bypass conduit 710 and between the T-junction 703 and the flow channel 604 to adjust the flow rate through the flow channel 604. Alternatively, the velocity of the sheath fluid flowing through the flow channel 604 may be adjusted using a fluid pump 701 driven by a variable speed brushless DC motor.

[0070] Peristaltic Pump 80 A peristaltic pump 80 according to one embodiment of the disclosure is shown in FIG. 17. The pump includes a housing 809 having an arcuate curved track 808, three rollers 810, 811, and 812 mounted on a rotor 816 rotatable within the housing 809, and a compressible tube 807 sandwiched between the housing 809 and the rollers 810, 811, and 812. As shown generally in FIGS. 18A-18D, the rollers 810, 811, and 812 of the peristaltic pump 80 are spaced from one another at substantially equal angular distances, separations, or intervals around the rotor 816. For clarity, the following description will assume that the rotor 816 rotates counterclockwise, but it should be understood that the description applies equally to peristaltic pumps having rotors that rotate clockwise. The compressible tube 807 of the housing 809 can be divided into several sections: 1. An opening between points 801 and 806 that is not subjected to compression; 2. A pump inlet section between points 801 and 802 which is continuously compressed to a fully closed condition as the roller rolls over this section; 3. Two pump sections, between points 802 and 803, and between points 804 and 805, which are completely closed by rollers; 4. A recessed portion between points 803 and 804 that expands continuously from a fully closed condition to a fully open condition as the roller rolls through the expansion of the recessed portion from point 803 to point 813; and 5. It is then compressed continuously from point 813 to point 804 until it is fully closed as the roller rolls through the compressed portion of the recessed portion. 6. An outlet section between points 805 and 806 which expands continuously from a fully closed condition to a fully open condition as the roller rolls through this section.

[0071] In other words, as the roller rolls counterclockwise on from the entry point 801 to the exit point 806, the internal clearance is 1. Continuously decreasing from a fully open state at point 801 to a fully closed state at point 802 and remaining closed until point 803; 2. Then it continues expanding again until it reaches full aperture at point 813; 3. Thereafter, it continuously decreases to a fully closed condition at point 804 and remains closed until the roller reaches point 805; 4. Finally, it continues expanding again to the fully open condition at point 806.

[0072] The size of the internal gap is shown diagrammatically in FIGS. 18A-18D as the distance between the dashed circle and the solid compressible tube 807. As shown in FIGS. 18A-18D, in the peristaltic pump 80 according to the present embodiment, the angular distance, separation distance, or spacing between points 801 and 803, between points 802 and 813, between points 813 and 805, and between points 804 and 866 correspond to the angles between adjacent rollers. Thus, as the roller 810 rolls through the pump portion from point 804 to point 805, as shown in FIGS. 18A-18B, the interaction completely determines the fluid flow rate of the peristaltic pump 80. When the roller 810 reaches the outlet portion between points 805 and 806 as shown in FIG. 18C, the lower part of the roller 810 starts to expand continuously and the gap starts to increase. Meanwhile, the roller 811 reaches the compression portion of the recessed portion and starts to compress continuously. In peristaltic pump 80, the shape of the compression of the concave portion between points 813 and 804 along compressible tube 807 is such that the volume of liquid displaced by compression under roller 811 in the compression of the concave portion between points 813 and 804 substantially fills the volume created by expansion under roller 810 in the outlet portion between points 5 and 6. During this period, the compressible is partially open under both rollers 810 and 811 and completely closed under roller 12. This causes the pumping action to be primarily achieved by roller 12. Specifically, by design, the total volume of liquid in the portion between points 13 and 6 remains substantially constant during this period, so that the flow rate of peristaltic pump 80 in the state shown in FIG. 18C remains substantially the same as the flow rate in the state shown in FIGS. 18A and 18B. As roller 810 passes point 806, roller 811 reaches the pump portion between points 804 and 805. It should be noted that because there is no physical distinction between rollers 810, 811, and 812, the flow rate of peristaltic pump 80 remains substantially constant throughout the process.

[0073] The mechanism of the non-pulsating peristaltic pump of the present disclosure can be more clearly understood when viewed along a circular coordinate system according to the roller motion. Referring to Fig. 19, the volume of fluid inside the compressible tube 819 from the outlet to the nearest roller 820 that blocks the compressible tube 819, i.e., the amount of fluid represented by the shaded area 818 shown in Fig. 19, is represented as V. Obviously, V depends on the angular position θ of the roller 20 and the amount of tube compression δ applied by all other downstream rollers. TIFF0007675791000002.tif6128

[0074] This allows the flow rate F of the peristaltic pump to be related to the time derivative of Vc by the following equation: TIFF0007675791000003.tif9128

[0075] where R is the rotor speed and the subscripts are used to distinguish between downstream rollers. The first term on the right hand side of equation (2) represents the contribution from the roller blocking the tube. Thus, the partial derivative TIFF0007675791000004.tif8128 does not depend on θ. The summation term represents the contribution from all other downstream rollers which also partially compress the compressible tube 819. Here, ΔS is the cross-sectional area change due to compression of the compressible tube 819, and L is the length of the tube whose cross-sectional shape is affected by the tube compression. Thus, L is proportional to the tube compression δ and ΔS is the square of δ. 2 It will be clear to those skilled in the art that the volume of fluid loss ΔV due to compression of the tube by the rollers is proportional to TIFF0007675791000005.tif7128 where D is the inner diameter of the compressible tube and G is the minimum clearance shown in Figures 19, 19A and 19B, which is also shown in Figures 18A-18D by the spacing between the dashed circle and the solid compressible tube 807 of the housing 809. Now, referring to Figures 20A and 20B, in a circular coordinate system, Figure 20A corresponds to the state of the pump shown in Figures 18A and 18B. During this period, there is no roller downstream of roller 810', so the summation term in equation (2) vanishes. Figure 20B corresponds to the state of the pump shown in Figure 18C. It is blocked by roller 12' and partially compressed by rollers 810' and 811'. However, the volume changes caused by the two rollers 810' and 811' substantially cancel each other out. This causes the summation term in equation (2) to vanish as well. Thus, the flow rate of the peristaltic pump 80 remains substantially constant regardless of the position of the rollers.

[0076] The shape of the compressible tube 807 that satisfies the above requirements can be easily derived from formula (3). Referring to FIG. 18C, the gap G of the bow-shaped compressible tube 807 in the compressed portion of the concave portion between point 813 and point 804 is 13,4 , and the gap G of the bowed compressible tube 807 at the exit portion between points 805 and 806 5,6 But the following formula: 21, the total fluid volume of these two portions remains substantially constant. In peristaltic pump 80, the shape of pump housing 809 is symmetrical about its centerline, such that the inlet half of pump housing 809 is a mirror image of the outlet half of housing 809, as shown in FIG. 17. Thus, peristaltic pump 80 can operate in both counterclockwise and clockwise rotations with little pulsation, although it will be understood that symmetry is not required to achieve a pulsation-free peristaltic pump according to the present disclosure. For example, the gap G of arcuate compressible tube 807 in the portion between points 13 and 3 is symmetrical about its centerline, such that the inlet half of pump housing 809 is a mirror image of the outlet half of housing 809, as shown in FIG. 17. 13,3, and the gap G of the bow-shaped compressible tube 807 in the portion between point 2 and point 1 2,1 However, the following equation (5): In accordance with TIFF0007675791000007.tif8128, the peristaltic pump according to the present disclosure exhibits little pulsation when rotor 816 rotates clockwise.

[0077] Figure 22 shows an alternative embodiment of a peristaltic pump according to the present disclosure. Those elements shown in Figure 22 that are common to peristaltic pump 80 shown in Figure 17 are given the same reference numbers distinguished by a prime (') symbol. Peristaltic pump 80' includes a compressible tube 807' having two recesses 820 and 821, and four rollers 822, 823, 824 and 825. In the embodiment shown in Figure 22, the volumetric loss of fluid due to tube expansion near the pump outlet is compensated for by the combined effect of compression of the compressible tube by rollers 822 and 823 near the two recesses 820 and 821.

[0078] FIG. 23 illustrates yet another alternative embodiment of a peristaltic pump according to the present disclosure. Those elements illustrated in FIG. 23 that are common to peristaltic pump 80 illustrated in FIG. 17 and peristaltic pump 80′ illustrated in FIG. 22 are labeled with the same reference numerals, distinguished by a double prime (″) symbol. Peristaltic pump 80″ includes six rollers and an arcuate compressible tube 807″ having two recesses 818″ and 819″. In peristaltic pump 80″, fluid volume loss due to tube expansion near the pump outlet is compensated for by the action of the rollers immediately upstream of one of the recesses 818″ or 819″ near the pump outlet.

[0079] Pulsations due to the expansion of compressed compressible tubing near the outlet of the peristaltic pump can also be overcome by a peristaltic pump with programmable rotor speed. Figures 24A-24C show relevant aspects of an alternative embodiment mechanism for minimizing peristaltic pump pulsation according to the present disclosure for a three-roller peristaltic pump. As shown in Figure 24B, the track 828 is substantially circular between the pump inlet and pump outlet portions. This allows the compressible tubing to be fully blocked by any one of the pump's three rollers 826, 827 and 829 between the pump inlet and pump outlet, as shown by the spacing between the dashed circle 829 and the solid curve of the track 828. Figure 24A shows roller positions in a circular coordinate system for the peristaltic pump shown in Figure 24B. Equation (2) becomes simpler since there is only one roller downstream of the roller that blocks the tubing. TIFF0007675791000008.tif8128

[0080] Here, tube compression δ(θ) is explicitly expressed as a function of roller position θ. The terms in brackets represent the rate of change of fluid volume with respect to roller position. The first term is the contribution from the roller blocking the tube, i.e., roller 827 in FIG. 24A, and the second term is the contribution from the roller at the outlet section. Note that by definition, the rate of volume change is negative and the second term in brackets vanishes if there is no roller at the outlet section. The dotted curve in FIG. 24C is a representative plot of the negative rate of volume change with respect to roller position. Bumps along the curve due to tube expansion as the roller rolls away from the tube near the pump outlet cause pulsation in a conventional peristaltic pump with a constant rotor speed. However, for the peristaltic pump shown in FIGS. 24A-24C, the rotor speed R, shown by the dashed curve in FIG. 24C, is set to vary synchronously with the rotor position and inversely proportional to the rate of change of fluid volume. This ensures that the pump flow rate, which is the product of rotor speed and rate of change of fluid volume, remains constant, as shown by the solid line at the top of Figure 24C. Note that the terms in brackets in equation (6) are uniquely determined by the mechanical structure of the pump. Thus, the rotor speed profile can be easily generated from the shape of track 828 according to equation (3). For those skilled in the art, there are numerous ways to realize a programmable rotor, for example using stepper motors or DC servo motors.

[0081] WDM equipment 90 FIG. 25 shows an optical ray trace for an exemplary 6-port wavelength division multiplexer of the present disclosure using a zigzag configuration. As shown in FIG. 25, the fluorescent light passing through a pinhole or emitted from the end face of a multimode optical fiber, such as optical fiber 852 shown in FIG. 1, forms a dispersed object or source at location 901, i.e., the optical input of the WDM 90. The size of the object is defined by the diameter of the pinhole or the core diameter of the multimode optical fiber. Note that the practical size of the pinhole or the core diameter of the multimode optical fiber is measured in millimeters, in contrast to the diameter of a single mode optical fiber, which is measured in micrometers. This makes the etendue of the fluorescent light source, defined as the product of the beam size and its divergence angle, hundreds of times larger than its counterpart in optical communications. According to the étendue conservation theorem (Julio Chaves, Introduction to Nonimaging Optics, CRC Press, 2008 [ISBN 978-1420054293]), light from such distributed sources, like light from a flash light, can only remain collimated over a very limited distance, especially if the diameter of the collimated part needs to be small.

[0082] As shown in FIG. 25, a collimating optic, in this case an achromatic lens 902, captures light from a light source 901 and projects a magnified image of the object near the final focusing lens 905. The size of the image near 905 is kept approximately the same as the effective size of the collimating optic 902. This effectively collimates the light beam propagating between lens 902 and lens 905. As shown in FIG. 25, a simple single lens 905 can be used to easily focus the collimated light beam to a spot smaller than the spot of the light beam received by WDM 90 at location 901, as long as the magnification is kept small, for example less than about 10. The ability to focus the light beam to such a small size allows a small area semiconductor detector to be placed at the focal point 906 of focusing lens 905 for efficient light detection.

[0083] A dichroic filter 903 oriented at an oblique angle is inserted into the optical path approximately halfway between the collimating optic 902 and the lens 905. The dichroic filter 903 passes the color band of interest and reflects the remaining colors of the light beam for further processing in the WDM 90. An optional bandpass filter 904 is inserted after the dichroic filter 903 to further improve the color separation performance of the WDM 90.

[0084] The light reflected from the dichroic filter 903 is incident on a second optical element 907, preferably a concave mirror. The concave mirror 907 has a radius of curvature approximately equal to the distance between the collimating optical element 902 and its image near the focusing lens 905. Thus, the concave mirror 907 forms a second image of the collimating lens 902 near the second focusing lens 908. The light beam between the concave mirror 907 and the second image at the lens 908 has substantially the same diameter as the light beam between the collimating lens 902 and the first image near the focusing lens 905. Thus, the relay imaging concave mirror 907 effectively doubles the collimated beam path without expanding the beam diameter. Again, the expanded and collimated beam can be easily focused to a spot smaller than the spot of the light source 901. A second dichroic filter 909 is then inserted approximately halfway between the relay imaging concave mirror 790 and the second image near the focusing lens 908. The second dichroic filter 909 passes another color band within the light beam received by WDM 90 at location 901 and reflects the remainder of the incident light beam for further processing.

[0085] As shown in Figure 25, additional relay collimating optics 910, 911, 912, 913 and dichroic filters 914, 915, 916, 917 can be similarly cascaded to generate multiple images proximate focusing lenses 918, 919, 920, and 921, each corresponding to a particular color band of light received by WDM 90 at Position 1. As shown in Figure 25, with the 1:1 image relay architecture of the present disclosure, the spots of light generated by focusing lenses 906, 908, 918, 919, 920, and 921 are all smaller than the source of the light beam and therefore can be easily captured by a small area APD.

[0086] 25 shows a six-port wavelength division multiplexer for light beams from a distributed light source, but one skilled in the art will readily appreciate that WDMs with different numbers of ports can be easily constructed according to the present disclosure. It will also be apparent to one skilled in the art that the WDM 90 preferably uses an achromat as the first collimating optical element, but a single lens can also be used, since the images produced before the focusing lenses 906, 908, 918, 919, 920 and 921 are all nearly monochromatic. Instead of using a concave mirror to relay the light beam reflected from the dichroic filter, it is also possible to use a refractive optic as a relay element to extend the path of the collimated light beam. However, a clear advantage of the zigzag architecture used in the WDM 90 is the possibility of using an array detector, resulting in a more compact WDM suitable for portable devices.

[0087] FIG. 26 shows an optical ray trace for a prior art collimating device. The method shown in FIG. 26 is widely used in conventional multi-color fluorescence instruments, for example as disclosed in U.S. Pat. No. 6,683,314. As shown in FIG. 26, the light beam diverges rapidly beyond the image 924 created by the collimating optical element 923. This makes it the only option for building a multi-color device to insert a dichroic filter between the collimating element 923 and its image 924.

[0088] Due to etendue conservation constraints, the diameter of the collimated beam must expand considerably to accommodate multiple dichroic filters in this section. The expansion of the beam poses significant challenges in refocusing the collimated beam to a small spot suitable for a small-area semiconductor detector. To overcome these difficulties, some instrument manufacturers have chosen to use Mt for fluorescence detection only, for example in mainstream flow cytometers manufactured by Becton-Dickinson, Becman Coulter, and Partec, and in the MegaBACE series of DNA sequencers by GE Amersham. Other instruments, such as the Luminex multiplex beam analyzer, select specific color bands containing known bright fluorescence and use large-area APDs to detect light within the selected color bands.

[0089] Figure 27 is a perspective view of an alternative embodiment for a 6-port WDM 90 using a combination of zigzag and drop configurations. The design is a modification of the zigzag configuration shown in Figure 25. In the alternative embodiment shown in Figure 27, the bandpass filter 904 of Figure 25 is replaced by a dichroic filter 904'. The filter 904' is positioned to pass one color and reflect the other color at 90°. The optical path lengths of the light beams passing through the dichroic filter 904' and reflected from 904' are substantially the same, which allows one arm to be focused by lens 905 and the other arm by lens 905' to a small spot that fits the small area semiconductor detectors located at the focusing positions 906 and 906'. As shown in FIG. 25, the remaining colors of light reflected by dichroic filter 903 are relayed by concave mirror 907, and the configuration including optical elements 903, 904', 905 and 905' is cascaded two more times to form a 6-port WDM.

[0090] Figure 28 shows a perspective view of an alternative embodiment for an eight-port WDM 90. By replacing the relay imaging concave mirrors 907 and 910 in Figure 27 with concave dichroic filters 907' and 910', the WDM shown in Figure 28 provides two more color bands compared to the WDMs shown in Figures 25 and 27.

[0091] A large number of fluorescent probes for use in flow cytometry have been developed over the years. More recently, multiple fluorescent proteins have also become important tools in biomedical research. To accommodate different types of fluorescent probes, various techniques have been developed to allow the user to select the dichroic filter that is appropriate for the user's specific needs. A key challenge with interchangeable dichroic filters is to avoid direct contact of the coated filter surface with the rigid flow cytometer reference frame. Repeated direct contact between the coated filter surface and any rigid reference frame can damage the interchangeable dichroic filter. Currently, most conventional solutions to this problem use precision machined mechanical spacers to hold the interchangeable dichroic filter in place. An example of such a solution is disclosed in U.S. Pat. No. 6,683,314. However, such a solution requires a detector active area of ​​less than 1.0 mm 2 If it is less than this, the reliability is poor.

[0092] 29A and 29B show the fabrication of an interchangeable dichroic filter assembly 934 shown in FIG. 29C, which is suitable for a small area detector. The assembly of the interchangeable dichroic filter assembly 934 starts from FIG. 29A, which shows the construction of a reference template for its fabrication. The reference template is a stepped structure made of two optically parallel glass plates 925 and 926. The two glass plates 925 and 926 are bonded together in optical contact, ensuring that the surface 929 of the glass plate 925 is optically parallel to the surface 930 of the glass plate 926. The front surface 932 of the interchangeable dichroic filter 927 is then pressed against the surface 929 of the template. A filter holder 928, which loosely fits the dichroic filter 927, includes a reference surface 931 and a filter slot 933. During assembly of the interchangeable dichroic filter, the filter slot 933 is partially filled with epoxy adhesive and the reference surface 931 of the filter holder 928 is pressed against the surface 930 of the template while the filter holder 928 slides towards the dichroic filter 927. While the epoxy adhesive is setting, a portion of the dichroic filter 927 remains fixed within the filter slot 933 while pressure is applied to the dichroic filter 927 and the filter holder 928. It will be apparent to one skilled in the art that the epoxy adhesive may be UV curable or heat curable, or may be made by blending the components of the A / B mixture. FIG. 29C shows E934~ made as shown in FIGS. 29A and 29B and described above. The assembly process shown in Figures 29A and 29B and described above ensures that the front surface 932 of the replaceable dichroic filter assembly 934 is optically parallel to the reference surface 931 and is recessed from the reference surface 931 by a distance precisely determined by the thickness of the glass plate 925.

[0093] 30A and 30B show an embodiment of the present disclosure in which the above-mentioned replaceable dichroic filter assembly 934 is used in a WDM 90 to optically process a light beam from a divergent light source. A notable feature of the WDM 90 is a glass reference block 935 having an optically flat surface. As will be apparent to one skilled in the art, the glass reference block 935 can be made of other materials. As shown in FIG. 30B, when installing a dichroic filter 927, the reference surface 931 of the replaceable dichroic filter assembly 934 slides against the flat surface of the glass reference block 935 and is held in contact therewith by a spring-loaded screw 936. This keeps the coated front surface 932 of the replaceable dichroic filter assembly 934 optically parallel to the optical plane and accurately positioned. Meanwhile, the recession of the front surface 932 relative to the reference surface 931 protects the reference surface 931 from physical contact with any object during filter replacement.

[0094] It will be apparent to those skilled in the art that numerous modifications and variations of the described embodiment of the interchangeable dichroic filter assembly 934 are possible. For example, an alternative embodiment of the present disclosure is a pedestal assembled using a first and a second circular optical flat. When assembling the interchangeable dichroic filter assembly 934, the reference surface of the filter holder abuts the first optical flat, and the coated surface of the dichroic filter abuts the second optical flat. Then, by epoxy bonding, the coated surface of the dichroic filter is held optically parallel to the reference surface of the filter holder, yet recessed by a distance precisely determined by the thickness of the second optical flat.

[0095] Industrial Applicability Having described in detail one embodiment of the present disclosure of an LD-based optical system for flow cytometry applications, and similarly advantageous embodiments for stream-based flow cytometry instruments, it will be apparent to those skilled in the art that numerous modifications and variations of the described embodiment are possible in light of the above teachings without departing from the principles and concepts of the present disclosure as set forth in the appended claims.

[0096] Having described in detail one embodiment of the present disclosure of a wavelength division multiplexer for separating a light beam from a distributed light source into multiple color bands, as well as several other equally advantageous embodiments, it will be apparent to those skilled in the art that numerous modifications and variations of the described embodiment are possible in light of the above teachings without departing from the principles and concepts of the present disclosure as set forth in the appended claims.

[0097] Although the present invention has been described in terms of the presently preferred embodiments, it should be understood that such disclosure is intended to be illustrative only and should not be interpreted as limiting the present disclosure. Thus, without departing from the spirit and scope of the present disclosure, various changes, modifications, and / or alternative uses of the present disclosure will undoubtedly be presented to those skilled in the art after reading the foregoing disclosure. Therefore, it is intended that the appended claims be interpreted as encompassing all changes, modifications, or alternative uses that are within the true spirit and scope of the present disclosure.

Claims

1. 1. A compound optical objective lens for a particle analyzer, comprising: a concave mirror configured to collect light from an observation zone configured to observe particles and to reflect the collected light to form an image; a corrective lens disposed to receive the reflected light from the concave mirror, the corrective lens including an aspheric surface having an intermediate zone and configured to reduce optical aberrations caused by the concave mirror in the reflected light; and A compound optical objective lens comprising:

2. The compound optical objective of claim 1 , wherein the intermediate zone is a circular intermediate zone.

3. The compound optical objective lens of claim 2 , wherein the circular intermediate zone is configured not to deflect light rays passing through the correcting lens.

4. the image is an image of the observation zone, and the correction lens is configured to reduce the optical aberration caused by the concave mirror based on the reflected light passing through the correction lens.

2. The compound optical objective lens of claim 1.

5. the concave mirror comprises a plano-concave mirror including a spherical mirror surface; the corrective lens comprises a plano aspheric lens; and the observation zone is located between the concave mirror and the correction lens; 2. The compound optical objective lens of claim 1.

6. The compound optical objective of claim 1 , wherein the corrector lens includes one aspheric surface.

7. 2. The composite optical objective lens of claim 1, wherein the concave mirror is configured to collect light emitted from a plurality of spatially separated positions in the observation zone and to reflect the collected light through the correction lens to form a plurality of corresponding images relative to an image plane.

8. The compound optical objective of claim 1 , wherein the intermediate zone is located between the first zone and the second zone.

9. the first zone has a negative refractive power; and the second zone having a positive refractive power; 9. The compound optical objective lens of claim 8.

10. the first zone is disposed outside the intermediate zone; the second zone is disposed inwardly of the intermediate zone; the thickness of the corrective lens is thinnest in the first zone; the thickness of the corrective lens in the second zone is greater than the thickness of the corrective lens in the intermediate zone; or It is a combination of these, 9. The compound optical objective lens of claim 8.

11. Particle analyzer, including: The composite optical objective lens according to claim 1; and A detector configured to measure the intensity of the light corrected by the correction lens.

12. 12. The particle analyzer of claim 11, wherein the detector is configured to receive light corrected by the correcting lens.

13. 12. The particle analyzer of claim 11, further comprising an optical fiber disposed in an optical path between the correction lens and the detector.

14. The optical fiber, Located near the image plane of the concave mirror; configured to transmit the light corrected by the correction lens to a wavelength division multiplexer for optically separating the light into at least two color bands; or It is a combination of these, A particle analyzer according to claim 13.

15. A flow cytometer comprising the particle analyzer of claim 11.

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