Beam forming with focus position adjustment

Abstract

The apparatus includes a beam source, a beam forming optics, a first focusing lens having a focal length, a second focusing lens having a focal length similar to the focal length of the first lens, and a lens translator configured to laterally move the second lens relative to the beam forming optics and the first lens, thereby laterally moving the elongated focus. In some embodiments, the beam forming optics is located between the beam source and the first focusing lens, the first focusing lens is located between the beam forming optics and the second focusing lens, and the beam forming optics, the first focusing lens, and the second focusing lens are arranged to receive a beam of laser radiation from the beam source and form the beam into an elongated focus.

Description

[0001] Priorities

[0002] This application claims priority to U.S. patent application serial number 16 / 393,545, filed on April 24, 2019, the disclosure of which is incorporated herein in its entirety. Technical Field

[0003] The present disclosure relates generally to projection lenses. In particular, disclosed herein are apparatus and methods for reducing degradation of a beam intensity profile when repositioning the focus of the beam. Background Art

[0004] The basic principle of flow cytometry is that particles in a fluid stream pass through a focused beam of laser radiation. Particles, particularly biological cells, can be detected, identified, counted and classified. Cellular components are fluorescently labeled and then illuminated by the laser radiation. The scattered and emitted radiation can be measured to determine the number and type of cells present in the sample.

[0005] Several detectors are carefully placed around the point where the fluid stream passes through the focused laser beam. Suspended particles, which may range in size from 0.2 to 150 micrometers (μm), pass through the focused laser beam and scatter the laser radiation. Fluorescently labeled cellular components are also excited by the focused laser beam and emit radiation (fluorescence) at a longer wavelength than the laser beam. This combination of scattered radiation and fluorescent radiation is measured by the detectors. The measurement data are then analyzed by a computer connected to the flow cytometer using special software. Thousands of particles can be measured and analyzed per second.

[0006] In flow cytometry (as in many applications), the beam intensity distribution at the laser focus significantly affects accuracy. Particles scatter radiation and emit radiation according to the laser intensity at the focus; variations in intensity at the focus cause variations in scattering and emission, leading to erroneous measurements. If the intensity varies, so does the scattering and emission, so the detector will not be able to consistently identify the same particle type: depending on where it is in the stream, a particle may or may not be detected. In flow cytometry, the desired beam profile is a "flat top," which can be understood to mean that the intensity of the beam is distributed over a portion of the focus in essentially a rectangular profile. Tolerances are very tight, and there is little room for intensity variations.

[0007] Movement of the beam focus results in degradation of the beam intensity distribution at the focus. Some applications require movement of the beam focus during use. Some systems are modular and require movement of the beam focus during setup. For example, flow cytometry components (e.g., optics, detectors, fluidics) are often sold separately and then assembled together. Flow cytometry modularity offers more applications and more parameter choices within applications. For example, laser beams with different wavelengths can be combined with different detector arrangements.

[0008] Flow cytometry components are often highly indexed to facilitate modular assembly, but often require adjustment after assembly. In some cases, the focus of the optical system must be adjusted to accommodate misalignments during assembly, such as misalignments between the optical device and the fluidics system. However, focus adjustment changes the beam intensity distribution, which can negatively affect the effectiveness of laser applications. SUMMARY OF THE INVENTION

[0010] Advantageously, the apparatus and methods described herein can reposition the focus of a beam while reducing degradation of the beam intensity profile. In one aspect, an apparatus includes a beam source, a beam forming optic, a first focusing lens having a focal length, a second focusing lens having a focal length similar to the focal length of the first lens, and a lens translator configured to laterally move the second lens relative to the beam forming optic and the first lens and thereby laterally move the elongated focus. In some embodiments, the beam forming optic is located between the beam source and the first focusing lens, the first focusing lens is located between the beam forming optic and the second focusing lens, and the beam forming optic, the first focusing lens, and the second focusing lens are arranged to receive a beam of laser radiation from the beam source and form the beam into an elongated focus.

[0011] In one aspect, a method of converting the focus of a laser beam includes generating a laser radiation beam, forming the beam using a beam forming optical device, focusing the formed beam to an elongated focus using a first focusing lens and a second focusing lens (the first focusing lens is located between the beam forming optical device and the second focusing lens), and laterally moving the elongated focus by laterally moving the second lens relative to the beam forming optical device and the first lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments by way of illustration and, together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0013] Figure 1A is a side view schematically illustrating an apparatus according to an embodiment, the apparatus comprising a beam source, a beam forming optical device, a first focusing lens, a second focusing lens, a lens translator, and a flow cell. Figure 1B It is schematically shown Figure 1A A floor plan of the equipment.

[0014] Figure 2A is a schematic diagram illustrating that after the lens translator moves the second focusing lens laterally in the first direction relative to the beam forming optics and the first lens, thereby moving the elongated focal point laterally in the first direction Figure 1A Side view of the device. Figure 2Bis a schematic diagram showing that after the lens translator moves the second focusing lens laterally in the second direction relative to the beam forming optics and the first lens, thereby moving the elongated focal point laterally in the second direction Figure 1A A floor plan of the equipment.

[0015] Figure 3A 1 is a graph of normalized intensity versus vertical distance illustrating the effect of beam movement on Gaussian beam intensity profile according to an embodiment. The graph provides normalized intensity before beam focus movement, after a pair of focusing lenses are simultaneously moved 1.5 mm, after the first focusing lens is moved 3.0 mm, and after the second focusing lens is moved 3.0 mm. Figure 3B is a graph of normalized intensity versus horizontal distance on a flat-top intensity distribution according to an embodiment. The graph provides an intensity distribution before the beam focus is moved, and provides exemplary intensity distributions corresponding to different mechanisms for moving the beam focus.

[0016] Figure 4A is a graph of normalized intensity versus horizontal distance illustrating exemplary top hat beam intensity distributions for beams having different coefficients of variance ("CV") and contained powers ("CP"), according to an embodiment. Figure 4B is a graph of CV versus horizontal focus displacement according to an embodiment. The graph provides CVs corresponding to focus displacements for moving a pair of focus lenses together, moving a first focus lens, and moving a second focus lens. Figure 4C is a graph of CP versus horizontal focus displacement according to an embodiment. The graph provides CP corresponding to focus displacements of moving a pair of focus lenses together, moving a first focus lens, and moving a second focus lens. Figure 4D is a graph of vertical Gaussian beam width versus focus displacement according to one embodiment. The graph provides vertical Gaussian beam width corresponding to focus displacements of moving a pair of focusing lenses together, moving a first focusing lens, and moving a second focusing lens.

[0017] Figure 5 is a method of translating the focus of a light beam according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Turning now to the drawings, wherein like features are represented by like reference numerals. Figure 1A1 is a side view schematically illustrating an apparatus 100 for focusing a laser beam according to an embodiment of the present invention. The apparatus 100 includes a beam source 102 that produces a beam 112, a beam forming optics 104, a first focusing lens 106, a second focusing lens 108, a lens translator 110a, and an (optional) sensor 120a. The beam 112 is depicted by a central ray 112b and peripheral rays 112a and 112c. The beam forming optics 104 is located between the beam source 102 and the first focusing lens 106, and the first focusing lens 106 is located between the beam forming optics 104 and the second focusing lens 108.

[0020] The beam forming optics 104 , the first focusing lens 106 and the second focusing lens 108 are arranged to receive a beam 112 of laser radiation from the beam source 102 and to form the beam 112 into an elongated focus 116 . Figure 1A The minor axis of the elongated focus is depicted.

[0021] like Figure 1A As shown in the embodiment of FIG. 1 , the apparatus 100 provides illumination for a flow cytometry system, wherein a fluid 118 flows in a flow cell 114. Figure 1A As shown in FIG, fluid 118 falls through flow cell 114 due to gravity. In the following, the orientation and arrangement of elements and light beams in apparatus 100 will be discussed with reference to the Cartesian axes X, Y and Z depicted in the drawings.

[0022] Flow cytometry is provided throughout this disclosure as an example application to illustrate features of the disclosure, but it should be understood that the disclosure is not limited to a particular application. The apparatus and methods disclosed herein can be used for other applications that benefit from degradation of the intensity distribution when the focus is moved.

[0023] In some embodiments, the beam source 102 provides a laser source for the device 100. When used for flow cytometry, the beam source 102 can provide multiple laser beams with different wavelengths. Exemplary methods and apparatus for focusing two or more laser beams with different wavelengths into a common focal spot are disclosed in U.S. Patent Application No. 15 / 883,542 (incorporated herein by reference in its entirety for all purposes) and U.S. Patent Application Publication No. 2018 / 0017769 (incorporated herein by reference in its entirety for all purposes).

[0024] The beam source 102 directs the beam 112 onto the beam forming optics 104. Exemplary methods and apparatus for beam forming are disclosed in U.S. Patent Application No. 15 / 883,542 (incorporated herein by reference in its entirety for all purposes) and U.S. Patent Application Publication No. 2018 / 0017769 (incorporated herein by reference in its entirety for all purposes).

[0025] In some embodiments, beam source 102 generates a Gaussian beam. In plane YZ depicted in the figure, lens 104a expands and lens 104b collimates the Gaussian beam. Powell lens 104c intercepts the expanded collimated Gaussian beam and is oriented to have no focusing power in plane YZ. Beam forming optics 104 are exemplary. In some embodiments, the beam forming optics may include more or less than Figure 1A-Figure 2B For example, the beam forming optics may consist of a single optical element.

[0026] In some embodiments, the components of system 100 are modular. In some embodiments, beam source 102 and beam forming optics 104 are combined into a single unit and first focusing lens 106, second focusing lens 108, and lens shifter 110a (and / or lens shifter 110b, see below) are combined into another single unit. In some embodiments, beam forming optics 104, first focusing lens 106, second focusing lens 108, and lens shifter 110a (and / or lens shifter 110b, see below) can be a single module (e.g., Figure 1A ). Other modular components of the flow cytometry system may include a beam source (e.g., beam source 102), a flow cell (e.g., flow cell 114), a radiation measurement system (not shown), and a measurement processor (not shown). In some embodiments, the beam focusing optics (e.g., first focusing lens 106, second focusing lens 108, and lens translators 110a and / or 110b) are combined into one module. In embodiments with a sensor (e.g., sensor 120a), the sensor may be combined in the same or different module as the lens translator.

[0027] The first focusing lens 106 and the second focusing lens 108 are combined to provide a focusing assembly of the light beam 112. As used herein, a "focusing assembly" may be understood to refer to an optical system (e.g., a lens) for forming a light beam into a focus for an application. For example, the first focusing lens 106 and the second focusing lens 108 together form the light beam 112 into a focus that is located in a flow cell to illuminate particles flowing through a flow cytometer.

[0028] Figure 1B It is schematically shown Figure 1A FIG. 1 is a plan view of device 100. The figure depicts the device in the XZ plane. Figure 1B The peripheral rays 112a' and 112c' depicted in FIG. Figure 1A The peripheral rays 112a and 112c in FIG. The central ray 112b is the same as the central ray 112b'.

[0029] Except for the Powell lens 104c, all optical elements appear the same in plan view because these elements are rotationally symmetric about the Z axis. Other embodiments may include rotationally asymmetric elements, such as aspherical and cylindrical surfaces. The Powell lens 104c converts the expanded collimated Gaussian beam into a beam with an angularly uniform intensity distribution. The focal point 116 has a flat top intensity distribution along the X axis in the XY plane. The fluid 118 flowing in the flow cell 114 is depicted as a circle located approximately in the middle of the focal point 116.

[0030] In general, the beam forming and focusing optics produce a beam focal point that is elongated along the X-axis. A flat-top intensity profile along the X-axis in the focal point 116 is important for flow cytometry because cells will always scatter and emit radiation regardless of the cell's position in the flow as it passes through the focused beam. It is also important for reliable measurements that the intensity profile on the X- and Y-axes of the focal point remain constant.

[0031] In some embodiments, the focal length of the second focusing lens is similar to the focal length of the first focusing lens. As used herein, two lenses have similar focal lengths when the focal lengths differ by less than 20%. More preferably, the focal lengths differ by less than 10%, and most preferably, they differ by less than 5%. The first focusing lens 106 and the second focusing lens 108 together have a focusing capability equivalent to that of a single more powerful lens. The focal length f1 of the first focusing lens, the focal length f2 of the second focusing lens, the distance d between the first and second focusing lenses, and the equivalent single lens f3 have an approximate relationship When the focusing lens has a spherical shape, distributing the focusing power between two spatially separated lenses will advantageously reduce spherical aberration in the focused beam. The distance between the two lenses is much smaller than their focal lengths f1 and f2; in some embodiments, less than 10% of f1 and f2, more preferably less than 5% of f1 and f2. In this case, the third term in the above relationship is relatively small. Advantageously, two simple lenses with spherical shapes may be less expensive than optically equivalent aspherical lenses.

[0032] Each lens translator 110a and 110b is configured to translate the second lens 108 laterally in one of two axes relative to the longitudinal direction of the light beam 112 . Figure 2A and 2B (discussed further below) shows the second lens 108 after the lens shifters 110a and 110b have each laterally moved the second lens 108 relative to the beam 112, thereby laterally moving the elongated focal point in the corresponding directions. Figure 1A and 1B For the sake of illustration, the displacement of the elongated focus is exaggerated in the drawings.

[0033] As used herein, the light beam propagates in what is known in the art as a "longitudinal direction". The central ray of the light beam propagates approximately collinearly with the "optical axis" of the system. The "lateral direction" is orthogonal to the longitudinal direction. Moving the second lens may be understood to mean moving the second lens while keeping the other optical elements substantially stationary. Moving the second lens laterally does not exclude some incidental movement in the longitudinal direction. Generally, a purely lateral translation is preferred, but not required, to avoid moving the elongated focus in the longitudinal direction.

[0034] In some embodiments, lens shifters 110a and 110b are different shifters, and in other embodiments, lens shifters 110a and 110b represent portions of the same shifter. For example, lens shifters 110a and 110b can be portions of a lens shifter that surrounds (partially or completely) second focusing lens 108. In some embodiments, one or both of the lens shifters is a mechanical system that moves the lens in a direction transverse to the direction of propagation. Mechanical systems for moving lenses, such as manual translation stages, motorized translation stages, piezoelectric actuators, servo motors, and linear actuators, are commercially available and need not be described in detail to understand the principles of the embodiments herein.

[0035] In some embodiments, lens translator 110a and / or lens translator 110b are operably connected to controller 122a and / or controller 122b. Controller 122a and controller 122b can receive data from sensor 120a and / or sensor 120b, respectively, and translate second focusing lens 108 according to application parameters. For example, in flow cytometry, the sensor provides data about the position of the elongated focus relative to the flow of cells; the controller then sends a signal to the lens converter to align the elongated focus with the flow. In material processing applications, the sensor provides data about the position of the processing material relative to the intended target; the controller then sends a signal to the lens converter to align the laser focus with the intended target. In some embodiments, sensors 120a and 120b are different sensors, while in other embodiments, sensors 120a and 120b are parts of the same sensor. In some embodiments, controllers 122a and 122b are different controllers, while in other embodiments, controllers 122a and 122b are parts of the same controller. In some embodiments, the controller is combined with each converter or sensor in a single unit.

[0036] Figure 2A is a schematic diagram illustrating the operation of the lens translator 110a after the lens translator 110a laterally moves the second focusing lens in the Y direction relative to the beam forming optics and the first lens, thereby laterally moving the elongated focal point in the Y direction. Figure 1A A side view of the device. Figure 2A In the example, the translator 110 has moved the second focusing lens from its position in the Y direction. Figure 1A The position in has moved by a distance of 202. This results in Figure 1A and 2A The distance 204 between the focal positions changes. For example, this change may be necessary when the optical axis of the light beam 112 is not initially aligned with the flow cell 114, such as Figure 2A This adjustment is particularly useful when the flow cell assembly is integrated with the detector that is aligned during the manufacturing process.

[0037] Figure 2B Schematically illustrates after the lens translator 110b laterally moves the second focusing lens in the X direction relative to the beam forming optics and the first lens, thereby laterally moving the elongated focal point in the X direction. Figure 1A The floor plan of the equipment. Figure 2B In the example, the translator 110b has moved the second focusing lens from its Figure 1B The position in the X direction has moved by a distance of 206. This results in Figure 1B and 2B Such a change may be necessary, for example, when the optical axis of the beam 112 (depicted as a dashed line) is not initially aligned with the flow cell 114. Figure 2B shown.

[0038] Figure 3A is a graph of normalized intensity versus vertical distance that illustrates the effect of beam movement on the Gaussian beam intensity distribution at the focus 116 according to an embodiment. For comparison, individual intensity distributions are arranged on the graph with each distribution centered at a distance Y of 0 μm. The graph (and Figures 3B-4D The graphs in ) were generated using ZEMAX optical design software, available from Zemax LLC of Kirkland, Washington.

[0039] Figure 3A The curve graph in (and Figures 3B-4D The curve graph in the figure is based on the above Figures 1A-2B 104b) is a light beam having a wavelength of 488 nm, a beam diameter of 0.7 mm (e.g., the beam diameter at light source 102), a focal length of -18 mm for a first beam forming optic (e.g., beam forming optic 104a), a focal length of 36 mm for a second beam forming optic (e.g., beam forming optic 104b), a Powell lens having a fan angle of 179.5 degrees (e.g., Powell lens 104c), a focal length of 50 mm for a first focusing lens (e.g., lens 106), and an identical second focusing lens (e.g., lens 108).

[0040] The graph provides the normalized intensity before the beam focus is moved ("0 mm"), after both focusing lenses are moved by 1.5 mm ("106 & 108 = 1.5 mm Y"), after only the first focusing lens is moved by 3.0 mm ("106 = 3 mm Y"), and after only the second focusing lens is moved by 3.0 mm ("108 = 3 mm Y"). A displacement of 0 mm means that the optical axes of both focusing lenses are aligned with the optical axis of the expanded collimated beam. The curve "108 = 3.0 mm Y" may correspond to Figure 2A The second focusing lens 108 moves a distance 206 and the focal position moves a corresponding distance 208.

[0041] The graph provides the intensity distribution before the beam focus is moved (0 mm plot line) and provides exemplary intensity distributions corresponding to different mechanisms for moving the beam focus by 1.5 mm. Unexpectedly, the intensity distribution for moving the second focusing lens 106 (curve "106 = 3.0 mm Y") is different from the curve for moving both lenses together. Note that the first focusing lens and the second focusing lens are each moved 3.0 mm to move the focus by 1.5 mm because the two lenses each have half the focusing power of the two lenses combined. The inventors found that movement of the first focusing lens relative to the optical axis provides more intensity distribution degradation than moving the two lenses together. More importantly, the inventors found that lateral movement of the second lens relative to the beam forming optics and the first lens resulted in less degradation of the intensity distribution.

[0042] The effect of lens shift on the flat-top profile is more significant. Figure 3B are graphs of normalized intensity versus horizontal distance after moving one or both of the focusing lenses 106 and 108 in the X direction by the indicated displacements. The 0mm graph depicts a flat-top profile where the optical axes of the two focusing lenses are aligned with the optical axis of the expanded collimated beam transformed by the Powell lens 104c. The remaining graphs illustrate the effect on the flat-top profile after the focus of the beam is shifted by 1.5mm. The focus displacement graph using a tilted mirror (see below) shows a flat-top profile that is significantly distorted and widely distributed in the horizontal direction relative to the 0mm plot. The "106 & 108 = 1.5mm X" plot represents the two lenses moved together. Relative to the tilted mirror graph, moving the two lenses together shows a significant improvement in the flat-top profile, but still shows a decrease from the 0mm plot.

[0043] and Figure 3AAs with the intensity distribution in FIG. 1 , the flat-top profiles for moving only the first focusing lens 106 (curve "106=3.0 mm X") and moving only the second focusing lens 108 (curve "108=3.0 mm X") are significantly different from the plots for moving both lenses together. By moving only the second focusing lens 108, the inventors have discovered that the flat-top profile of the beam changes less from the 0 mm curve than if both lenses were moved together. This discovery may be particularly advantageous in applications that benefit from less degradation in the intensity distribution as the focus is moved. For example, moving only the second lens may allow flow cytometer cells to scatter and emit radiation consistently regardless of the cell's position in the flow as it passes through the focused beam.

[0044] Figure 4A 1 is a graph of normalized intensity versus distance showing exemplary flat-top intensity profiles for a beam having an ideal coaxial alignment along the optical axis and another alignment in which the lens 106 is displaced 3.0 mm from the optical axis in the X direction.

[0045] CV can be understood from the following equation

[0046]

[0047] The CV value indicates the "flatness" of the flat-top intensity distribution in the desired window. Figure 4A In the flow cytometer, a CV of less than 3% (more preferably less than 2%) is acceptable. Advantageously, the embodiments herein can maintain a CV of less than 3% (and in some cases, less than 2%) after moving the focus. Some embodiments described herein can maintain a CV of between 0.2% and 3% (more preferably between 0.2% and 2%) after moving the focus.

[0048] CP can be understood from the following equation

[0049]

[0050] The CP value represents the power in the desired window. In flow cytometer use, a CP greater than 50% (more preferably greater than 60%) may be acceptable. Advantageously, the embodiments herein can maintain a CP greater than 50% (and in some cases, greater than 60%) after moving the focus. After moving the focus, some embodiments described herein can maintain a CP between 50% and 80% (more preferably, between 60 and 80%).

[0051] Here, all CV and CP values ​​are for a moving 50 μm window. Essentially, the center of the 50 μm window is scanned across the intensity distribution and the minimum CV value and maximum CP value are provided. Figure 4A, two exemplary intensity profiles illustrate the dependence of the flat-top profile on CV and CP. The beam with a CV of 0.4% provides a flat-top profile that is nearly horizontal at the top of the profile relative to the beam with a CV of 2.4%. The beam with a CP of 61% concentrates more power within the 50 μm window 400 than the beam with a CP of 55%.

[0052] Figure 4B is a graph of CV versus horizontal focus displacement according to an embodiment. The graph provides the CV of the focus displacement corresponding to moving a pair of focus lenses together ("106 & 108X"), moving only the first focus lens ("106X"), and moving only the second focus lens ("108X"). The graph shows the unexpected improvement in CV by moving the second lens laterally relative to the beam forming optics and the first lens. Figure 4B As shown, improvements can be found regardless of the distance the focal spot is moved. Figure 4B The “focus shift” in the graph of can correspond to the above Figure 1B and 2B Movement in the X direction shown in .

[0053] Figure 4C is a graph of CP versus horizontal focus displacement according to an embodiment. The graph provides CP for focus displacements corresponding to moving a pair of focus lenses together ("106 & 108X"), moving only the first focus lens ("106X"), and moving only the second focus lens ("108X"). The graph shows the unexpected improvement in CP by moving the second lens laterally relative to the beam forming optics and the first lens. As shown in Figure 4C As shown, improvements can be found regardless of the distance the focal spot is moved. Figure 4C The “focus shift” in the graph of can correspond to the above Figure 1B and 2B Movement in the X direction shown in .

[0054] Figure 4D is a graph of vertical Gaussian beam width versus vertical focal displacement according to one embodiment. The graph provides vertical Gaussian beam widths for focal displacements corresponding to moving a pair of focusing lenses together ("106 & 108Y"), moving only the first focusing lens ("106Y"), and moving only the second focusing lens ("108Y"). These graphs illustrate that moving the second lens laterally relative to the beam forming optics and the first lens provides minimal beam degradation compared to the 0 mm plot. Figure 4D The “focus shift” in the graph of can correspond to the above Figure 1A and 2A Movement in the Y direction shown in .

[0055] Figure 5 is a method 500 of translating a beam focus according to an embodiment. The method 500 includes generating a beam of laser radiation 502, forming the beam using beam forming optics 504, focusing the formed beam into an elongated focus 506 using a first focusing lens and a second focusing lens, and laterally moving the elongated focus by laterally moving the second lens relative to the beam forming optics and the first lens 508. In some embodiments, the method 500 is performed by the apparatus 100 described above.

[0056] In some embodiments of method 500, the elongated beam includes a flat-top intensity profile. In some embodiments of method 500, the second lens is made of a high refractive index glass to further minimize spherical aberration. In some embodiments of method 500, the method further includes providing an additional focusing element.

[0057] In some embodiments of method 500, generating a light beam includes generating a Gaussian light beam, and the method further includes forming an angularly uniform light beam from the Gaussian light beam at a beam forming optical device, and forming a spatially uniform light beam in an illumination plane by focusing the angularly uniform light beam. As used herein, a spatially uniform light beam may be understood as a light beam having a flat-top intensity distribution at a focus of the light beam, as further described herein.

[0058] In some embodiments of method 500, the method further comprises illuminating the flow cell with the elongated focused light beam. In some embodiments, the method further comprises measuring radiation scattered and emitted from the flow cell.

[0059] In some embodiments of method 500, the method further includes receiving data regarding the position of the elongated focal point and sending a command signal to a lens translator to laterally move the second lens based on the data.

[0060] In some embodiments of method 500, the first focusing lens and the second focusing lens are separated. In some embodiments, the first focusing lens and the second focusing lens are separated by a distance less than 10% of the focal length of the first focusing lens. In some embodiments, the first focusing lens and the second focusing lens are separated by a distance less than 5% of the focal length of the first focusing lens.

[0061] In some embodiments of method 500, the focal lengths of the first focusing lens and the second focusing lens differ by less than 20%. In some embodiments, the focal lengths of the first focusing lens and the second focusing lens differ by less than 5%.

[0062] In some embodiments of method 500, the beam source and the beam forming optics are integrated into a single unit, and the first focusing lens, the second focusing lens, and the lens shifter are integrated into another single unit. In some embodiments, the beam forming optics, the first focusing lens, the second focusing lens, and the lens shifter are integrated into a single unit.

[0063] In some embodiments of method 500, laterally moving the elongated focus comprises maintaining a coefficient of variation between 0.2-3.0% after laterally moving the elongated focus. In some embodiments of method 500, laterally moving the elongated focus comprises maintaining a contained power between 50-80% after laterally moving the elongated focus.

[0064] return Figures 1A-2B In some embodiments, the focusing assembly includes an additional focusing element, such as a third lens, wherein the second lens is located between the first lens and the third lens, and the focal length of the third lens is longer than the focal length of the first lens or the second lens. For example, the focal length is at least five times longer than the first lens or the second lens. A translatable third lens having much weaker optical power than the first lens X and the second lens Y will provide additional finer lateral adjustment of the focus position.

[0065] Back to Figure 3B , an intensity distribution "mirror tilt" is generated for a device 100 having an additional fold mirror located between the beam forming optics and the focusing optics. In order to move the focal point 116, the fold mirror can be tilted, which changes the incident position and angle of the amplified collimated beam on the focusing lenses 106 and 108. A comparison in the figures shows that tilting the fold mirror causes significantly more distortion of the intensity distribution than moving the focal point by simply translating the second focusing lens 108. Therefore, such tilting introduces aberrations in the beam having multiple wavelengths, further distorting the beam.

[0066] The present invention has been described above with reference to preferred embodiments. However, the present invention is not limited to the embodiments described and depicted herein. On the contrary, the present invention is only limited by the appended claims. "Including," "comprising," "having," "containing," "involving," and variations thereof used herein are intended to include the items listed thereafter and their equivalents as well as other items, and do not exclude the presence or addition of one or more other features, integers, processes, operations, elements, components, and / or groups thereof. As used herein, the singular forms "a," "an," and "the" are also intended to include plural forms, unless the context clearly indicates otherwise.

Claims

1. Equipment, including: beam source; beam forming optics; a first focusing lens having a focal length; a second focusing lens having a focal length wherein The focal lengths of the first focusing lens and the second focusing lens differ by less than 20%. The beam forming optics is located between the beam source and the first focusing lens, The first focusing lens is located between the beam forming optics and the second focusing lens, and The beam forming optics, the first focusing lens and the second focusing lens are arranged to receive a beam of laser radiation from the beam source and to form the beam into an elongated focus; as well as A lens translator is configured to move the second focusing lens transversely to the longitudinal direction of the light beam and relative to the beam forming optics and the first focusing lens, thereby moving the elongated focal point transversely to the longitudinal direction of the light beam.

2. The device according to claim 1, wherein: The laser radiation beam has a flat-top intensity profile in a first lateral dimension at a focal point.

3. The device according to claim 1, wherein: The second focusing lens is made of high refractive index glass.

4. The apparatus of claim 1, further comprising a third focusing lens having a focal length longer than a focal length of the second focusing lens, and wherein the second focusing lens is located between the first focusing lens and the third focusing lens.

5. The device according to claim 1, wherein: The beam forming optical device includes a Powell lens, which converts a Gaussian beam provided by the beam source into an angularly uniform beam.

6. The apparatus of claim 1, further comprising a flow cell illuminated by the light beam.

7. The apparatus of claim 6, further comprising a radiation measurement system configured to measure radiation scattered and emitted from the flow cell.

8. The apparatus according to claim 1, further comprising: a sensor configured to provide data regarding the position of the elongated focal point; as well as A controller is configured to receive data from the sensor and send command signals to the lens translator to laterally move the second focus lens.

9. The device according to claim 1, wherein: The first focusing lens and the second focusing lens are separated by a distance less than 10% of the focal length of the first focusing lens.

10. The device according to claim 9, wherein: The first focusing lens and the second focusing lens are separated by a distance less than 5% of the focal length of the first focusing lens.

11. The device according to claim 1, wherein: The beam source and the beam forming optics are integrated into a single unit, and wherein the first focusing lens, the second focusing lens and the lens translator are integrated into another single unit.

12. The device according to claim 1, wherein: The beam forming optics, the first focusing lens, the second focusing lens and the lens translator are integrated into a single unit.

13. The apparatus according to claim 1, wherein: The focal lengths of the first focusing lens and the second focusing lens differ by less than 5%.

14. The apparatus according to claim 1, wherein: The first and second focusing lenses are configured to maintain a coefficient of variation between 0.2-3.0% after laterally shifting the elongated focus.

15. The apparatus according to claim 1, wherein: The first and second focusing lenses are configured to maintain a contained power between 50-80% after laterally moving the elongated focal point.

16. The apparatus according to claim 1, wherein: The lens translator is configured to move the second focusing lens relative to the beam forming optics and the first focusing lens transverse to a longitudinal direction of the light beam in two orthogonal axes.

17. The apparatus according to claim 1, wherein: The lens shifter is configured to move only the second focusing lens.

18. A method for translating a laser beam focus, the method comprising: generating a laser radiation beam; forming the light beam using beam forming optics; focusing the formed light beam into an elongated focus using a first focusing lens and a second focusing lens, wherein the first focusing lens is located between the beam forming optics and the second focusing lens; as well as The elongated focal point is moved transversely to the longitudinal direction of the light beam using a lens shifter configured to move the second focusing lens transversely to the longitudinal direction of the light beam and relative to the beam forming optics and the first focusing lens.

19. The method of claim 18, the light beam having a flat-top intensity profile in a first lateral dimension at a focal point.

20. The method according to claim 18, wherein: The second focusing lens is made of high refractive index glass.

21. The method of claim 18, further comprising providing a third focusing lens, wherein the second focusing lens is located between the first focusing lens and the third focusing lens, and wherein a focal length of the third focusing lens is longer than a focal length of the second focusing lens.

22. The method according to claim 18, wherein: Generating a light beam includes generating a Gaussian light beam, and the method further includes: Using a Powell lens, an angularly uniform beam is formed from a Gaussian beam, and a spatially uniform beam is formed in a plane from the angularly uniform beam.

23. The method of claim 18, further comprising illuminating the flow cell with the elongated focused light beam.

24. The method of claim 23, further comprising measuring radiation scattered and emitted from the flow cell.

25. The method of claim 18, further comprising: receiving data regarding a position of the elongated focus; as well as Based on the data, a command signal is sent to the lens shifter to laterally move the second focusing lens.

26. The method of claim 18, wherein: The first focusing lens and the second focusing lens are separate.

27. The method according to claim 18, wherein: The beam source and the beam forming optics are integrated into a single unit, and wherein the first focusing lens, the second focusing lens and the lens translator are integrated into another single unit.

28. The method of claim 18, wherein: The beam forming optics, the first focusing lens, the second focusing lens and the lens translator are integrated into a single unit.

29. The method of claim 18, wherein said moving the second focusing lens is performed without moving the first focusing lens.

30. A method for translating a laser beam focus in a flow cell using an apparatus comprising: beam source; beam forming optics; a first focusing lens having a focal length; a second focusing lens having a focal length wherein The focal lengths of the first focusing lens and the second focusing lens differ by less than 20%. The beam forming optics is located between the beam source and the first focusing lens, The first focusing lens is located between the beam forming optics and the second focusing lens, and The beam forming optics, the first focusing lens and the second focusing lens are arranged to receive a beam of laser radiation from the beam source and to form the beam into an elongated focus in the flow cell, The method includes: The elongated focus is laterally moved in the flow cell by moving the second focusing lens transversely to the longitudinal direction of the beam and relative to the beam forming optics and the first focusing lens.

31. The method of claim 30, wherein said moving said second focusing lens is performed without moving said first focusing lens.

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