PARTICLE DETECTION SYSTEM AND METHOD FOR PARTICLE DETECTION - Patent application

Abstract

SUMMARY OF THE INVENTION A particle detection system and method is disclosed. In one embodiment, the particle detection system includes an incident beam light source that emits an incident beam, a particle monitoring zone disposed in the path of the incident beam, a photodetector disposed to detect the incident beam after passing through the particle monitoring zone, and an excitation beam light source that emits an excitation beam directed toward the particle monitoring zone, wherein the incident beam, excitation beam, and photodetector are arranged such that the photodetector detects a combination of light from the incident beam, scattered light due to scattering of the incident beam in the particle monitoring zone, and scattered light due to scattering of the excitation beam in the particle monitoring zone.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 036,930, filed June 9, 2020, and U.S. Provisional Patent Application No. 63 / 079,382, filed September 16, 2020, the entire contents of each of which are incorporated herein by reference. BACKGROUND OF THE INVENTION

[0002]

[0002] Advances in technology requiring cleanroom conditions have necessitated the detection and characterization of increasingly small particles. For example, microelectronic foundries seek to detect particles less than 20 nm, and in some cases less than 10 nm, in size due to their potential impact on increasingly delicate manufacturing processes and products. Similarly, the manufacturing of pharmaceuticals and biomaterials requires sterile processing conditions, necessitating accurate characterization of biological and non-biological particles to address health and human safety compliance standards.

[0003]

[0003] Typically, these industries rely on optical particle counters for the detection and characterization of small particles. Being able to detect smaller particles requires new approaches to optical particle counting, such as systems employing increased laser power, shorter excitation wavelengths, and more complex techniques such as condensation nucleus counting, which can significantly increase the cost and overall complexity of devices capable of detecting nanometer-scale particles. These new approaches can also require more frequent calibration and maintenance to provide the necessary reliability and reproducibility.

[0004]

[0004] Various optical particle counters are known in the art, for example, U.S. Patent No. 7,916,293 provides a scattered light optical particle counter. Also, U.S. Patent Nos. 7,746,469, 9,983,113, and 10,416,069, U.S. Patent Application Publication Nos. 2019 / 0277745 and 2017 / 0176312, and WO 2019 / 082186 provide transmission / obstruction particle counters, including transmission / obstruction particle counters using structured beams and / or interferometry. The entire contents of these documents are incorporated herein by reference to describe the components and configurations of particle counter systems useful, particularly, for detecting and characterizing small particles.

[0005] From the foregoing, it can be seen that there is a need in the art for systems and methods for improving the optical detection of particles having small size dimensions. Summary of the Invention

[0006]

[0006] The present invention relates to particle detection. Systems and methods for particle detection are provided that exhibit improved signal-to-noise ratios, reduced sensitivity to thermal expansion, and / or reduced sensitivity to optical misalignment. At least some of these improvements, according to some embodiments herein, can be due to the optical combination and detection of scattered and unscattered incident light. Specifically, in some embodiments, a photodetector may be positioned in the optical path of a laser beam (i.e., the beam is incident on the photodetector) across a particle monitoring zone. The incident beam may be polarized (e.g., linearly polarized). Particles in the particle monitoring zone may cause forward-scattered light due to incident beam / particle interactions to be essentially coincident with and parallel to the incident beam. Thus, the photodetector may detect a combination of direct, unscattered light from the incident beam and light forward scattered by particles in the monitoring zone.

[0007] However, especially for small particles, the intensity of the direct, unscattered light from the incident beam can greatly exceed the intensity of the forward-scattered light, and the resulting signal-to-noise ratio can pose significant problems in signal interpretation. It has been found that a second laser beam can be directed at the particle such that additional scattered light from the particle (e.g., side-scattered light) is combined with the scattered and unscattered light from the incident beam. The second beam may be configured to produce scattered light that is essentially coherent and parallel to the incident beam and the forward-scattered light from the incident beam. Thus, in some embodiments, interference can occur between three types of light: (i) unscattered light from the incident beam, (ii) forward-scattered light from the incident beam, and (iii) scattered light from the second beam. Accordingly, the methods and apparatus herein may sometimes be referred to as "interferometric."

[0008] The combination of the three types of light may be directed onto a photodetector. The second beam may "excite" the scattered light component without significantly changing the intensity of the incident light component detected by the photodetector. This may significantly improve the sensitivity and / or signal-to-noise ratio of the particle detection system. Furthermore, the fluid sampling volume and / or volume sampling rate may be significantly improved, thereby reducing sampling time, especially for fluids with very low particle concentrations. The systems and methods disclosed herein may also be capable of detecting more particles than prior art (i.e., particles missed by prior art systems), because particles flowing through the flow cell too far from the center of the beam often pass undetected in prior art systems.

[0009] In some embodiments, the excitation beam may be directed at the particle monitoring zone at a right angle relative to the incident beam. In such embodiments, the right angle excitation beam configuration may result in side scattered light adding to the light combination detected by the photodetector. In other embodiments, the excitation beam may be directed at the particle monitoring zone at an oblique angle relative to the incident beam, which may result in oblique scattered light adding to the light combination detected by the photodetector. In yet other embodiments, the excitation beam may be directed at the particle monitoring zone at 180° relative to the incident beam, which may result in back scattered light adding to the light combination detected by the photodetector.

[0010] The systems and methods of the present invention provide for the detection of particles in a fluid stream (detection, counting, and sizing of single particles in a fluid stream). In one embodiment, the fluid is a liquid or a gas. In one embodiment, the system is for detecting particles in liquid chemicals. In one embodiment, the system is for detecting particles in ultrapure water. In one embodiment, the system is for detecting particles in high-pressure gases. In one embodiment, the system is for detecting particles in air. In one embodiment, the system is for detecting particles on a surface.

[0011] In one embodiment, a particle detection system includes an incident beam light source providing an incident beam, a particle monitoring zone disposed in the path of the incident beam and containing particles, a photodetector disposed to detect the incident beam after it leaves the particle monitoring zone, and an excitation beam light source providing an excitation beam directed into the particle monitoring zone. The incident beam, excitation beam, and photodetector may be arranged such that the photodetector detects a combination of light from the incident beam or a reference beam, scattered light due to scattering of the incident beam from particles in the fluid stream in the particle monitoring zone, and scattered light due to scattering of the excitation beam from particles in the fluid stream in the particle monitoring zone.

[0012] In one embodiment, the incident beam intersects the excitation beam at the monitoring zone.

[0013]

[0013] In one embodiment, the incident beam, excitation beam, and photodetector are arranged so that the photodetector detects a combination of light from the incident beam, scattered light due to scattering of the incident beam from particles in the particle monitoring zone, and scattered light due to scattering of the excitation beam from particles.

[0014]

[0014] In one embodiment, the incident beam, excitation beam, and photodetector are arranged so that the photodetector detects a combination of light from the reference beam, scattered light due to scattering of the incident beam from particles in the particle monitoring zone, and scattered light due to scattering of the excitation beam from particles.

[0015] In one embodiment, the reference beam is a homodyne interferometric reference beam.

[0016] In one embodiment, the reference beam is a heterodyne interferometric reference beam.

[0017] In one embodiment, a particle detection system includes an incident beam light source that emits an incident beam, a particle monitoring zone disposed in the path of the incident beam, a photodetector disposed to detect the incident beam after passing through the particle monitoring zone, and an excitation beam light source that emits an excitation beam. The excitation beam may be directed toward the particle monitoring zone. The incident beam, excitation beam, and photodetector may be arranged such that the photodetector detects a combination of light from the incident beam, scattered light due to scattering of the incident beam in the particle monitoring zone, and scattered light due to scattering of the excitation beam in the particle monitoring zone.

[0018] In one embodiment, the scattered light from the incident beam in the particle monitoring zone may be forward scattered light. In one embodiment, the particle detection system may include a laser and a polarizing beam splitter. The incident beam source may include light from the laser directed on a first optical path through the polarizing beam splitter. The excitation beam source may include light from the laser directed on a second optical path through the polarizing beam splitter.

[0019] In some embodiments, the incident beam is polarized before entering the monitoring zone. In some embodiments, the excitation beam is polarized before entering the monitoring zone. In one embodiment, both the incident beam and the excitation beam may be generated from a single light source, for example, via a polarizing beam splitter. The excitation beam may be modified by a half-wave plate. The incident beam may be modified by a half-wave plate. At the monitoring zone, the polarized incident beam and the polarized excitation beam may be configured such that the polarization axis of the incident beam is essentially the same as the polarization axis of the excitation beam. For example, in one embodiment, the polarization axis of the incident beam is within 5° of the polarization axis of the excitation beam. In one embodiment, the polarization axis of the incident beam is within 3° of the polarization axis of the excitation beam. In one embodiment, the polarization axis of the incident beam is within 2° of the polarization axis of the excitation beam. In one embodiment, the polarization axis of the incident beam is within 1° of the polarization axis of the excitation beam. In one embodiment, the polarization axis of the incident beam is within 0.1° of the polarization axis of the excitation beam.

[0020] Thus, in some embodiments, when the combination of light reaches the photodetector, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are essentially the same. For example, in one embodiment, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are within 5° of each other. In one embodiment, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are within 3° of each other. In one embodiment, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are within 2° of each other. In one embodiment, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are within 1° of each other. In one embodiment, the polarization axes of the scattered light from the incident beam, the scattered light from the excitation beam, and the light from the incident beam are within 0.1° of each other.

[0021]

[0021] In one embodiment, the particle detector may include a first laser and a second laser, the incident beam light source including light from the first laser and the excitation beam light source including light from the second laser.

[0022]

[0022] In one embodiment, the photodetector may generate a particle detection signal due to scattering in the particle monitoring zone, and the signal may correspond to the total irradiance of (i) light from the incident beam, (ii) light scattered by the incident beam, and (iii) light scattered by the excitation beam.

[0023] In one embodiment, the magnitude of the particle detection signal is at least two times greater than in the absence of the excitation beam. In one embodiment, the magnitude of the particle detection signal is at least four times greater than in the absence of the excitation beam. In one embodiment, the magnitude of the particle detection signal is at least ten times greater than in the absence of the excitation beam.

[0024] In one embodiment, the excitation beam intersects the particle monitoring zone at an oblique angle relative to the incident beam. In one embodiment, the excitation beam intersects the particle monitoring zone at a right angle relative to the incident beam. In one embodiment, the excitation beam intersects the particle monitoring zone in a direction opposite to the incident beam. In one embodiment, the scattered light due to scattering of the excitation beam in the particle monitoring zone is side scattered light. In one embodiment, the scattered light due to scattering of the excitation beam in the particle monitoring zone is back scattered light.

[0025] In some embodiments, the particle monitoring zone comprises a flow cell configured to flow particles.

[0026] In some embodiments, the particle monitoring zone comprises a surface on which particles are analyzed for presence, size, number, etc. For example, in one embodiment, the particle monitoring zone comprises a surface and an excitation beam is directed at the particle monitoring zone at an oblique angle relative to the incident beam, such that obliquely scattered light adds to the combination of light detected at the photodetector.

[0027] In one embodiment, the irradiance ratio of the excitation beam is at least 1, where the irradiance ratio is defined as the ratio of the irradiance at the waist of the excitation beam to the irradiance at the waist of the incident beam. In one embodiment, the irradiance ratio of the excitation beam is at least 2. In one embodiment, the irradiance ratio of the excitation beam is at least 10. In one embodiment, the irradiance ratio of the excitation beam is at least 100.

[0028] In some embodiments, the irradiance ratio of the excitation beams is less than 1. In some embodiments, the irradiance ratio of the excitation beams is between 1 and 2.

[0029] In some embodiments, the waist of the excitation beam is larger than the waist of the incident beam. For example, in one embodiment, the waist of the excitation beam is at least 1.5 times larger than the waist of the incident beam. In one embodiment, the waist of the excitation beam is at least 2 times larger than the waist of the incident beam. In one embodiment, the waist of the excitation beam is at least 3 times larger than the waist of the incident beam. In one embodiment, the waist of the excitation beam is at least 5 times larger than the waist of the incident beam.

[0030] In one embodiment, the average power of the excitation beam entering the particle monitoring zone is at least two times greater than the average power of the incident beam entering the particle monitoring zone. In one embodiment, the average power of the excitation beam is at least ten times greater than the average power of the incident beam. In one embodiment, the average power of the excitation beam is at least 100 times greater than the average power of the incident beam. In one embodiment, the average power of the excitation beam is at least 1000 times greater than the average power of the incident beam.

[0031] In one embodiment, the excitation beam is configured as a multi-path beam. In one embodiment, the incident beam is configured as a multi-path beam. In one embodiment, the excitation beam is configured as a dual-path beam. In one embodiment, the incident beam is configured as a dual-path beam.

[0032] In one embodiment, the excitation beam is a structured beam, for example, in one embodiment, the excitation beam is a dark beam.

[0033] In one embodiment, the incident beam is a structured beam. For example, in one embodiment, the incident beam is a dark beam.

[0034] In one embodiment, the incident beam is configured as a dual-pass dark beam. In one embodiment, the excitation beam is configured as a dual-pass dark beam. In one embodiment, the incident beam is configured as a multi-pass dark beam. In one embodiment, the excitation beam is configured as a multi-pass dark beam.

[0035] In one embodiment, the particle detection system is an excited homodyne interferometric detection system. In one embodiment, the particle detection system is an excited self-homodyne interferometric detection system. In one embodiment, the particle detection system is an excited heterodyne interferometric detection system.

[0036] In one embodiment, the incident beam passes through a cylindrical lens to produce a conventional high aspect ratio incident beam.

[0037] In some embodiments, the excitation beam may be a dual-path beam. For example, in one embodiment, the excitation beam may pass through the monitoring zone, be reflected back through a focusing lens and a mirror, and then pass through the monitoring zone again. The dual-path configuration of the excitation beam may improve sensitivity and / or count rate.

[0038] In one embodiment, the optical particle counter comprises the particle detection system. In one embodiment of the optical particle counter, the photodetector is a first photodetector and the optical particle counter comprises a second photodetector arranged to detect the excitation beam after passing through the particle monitoring zone.

[0039]

[0039] In some embodiments, the coupling between the excitation beam and the incident beam may be improved by employing (one or more) narrow linewidth lasers and / or (one or more) single frequency lasers for the excitation beam and / or the incident beam.

[0040] In one embodiment, the particle detection system is a differential detection system. In one embodiment, the differential detection system is used to reduce noise in the detector.

[0041] In one embodiment, the particle detection system may include a diffractive optical element disposed in the path of the incident beam between the incident beam source and the particle monitoring zone.

[0042] In one embodiment, the diffractive optical element is configured to generate a one-dimensional beam array. In one embodiment, the diffractive optical element is configured to generate a plurality of Gaussian beams.

[0043] In one embodiment, the diffractive optical element is configured to generate a plurality of beams, each of which has an intensity variance of less than 5% compared to the other beams.

[0044] In one embodiment, the photodetector includes an upper zone and a lower zone, hi one embodiment, the photodetector is a differential array detector.

[0045] In one embodiment, a particle detection system includes an incident beam source providing an incident beam, a particle monitoring zone disposed in the path of the incident beam and including a fluid stream having particles, a diffractive optical element disposed in the path of the incident beam between the incident beam source and the particle monitoring zone, and a photodetector disposed to detect the incident beam after passing through the particle monitoring zone. The incident beam and the photodetector may be arranged such that the photodetector detects light from the incident beam and scattered light resulting from scattering of the incident beam from particles in the fluid stream in the particle monitoring zone.

[0046] In one embodiment, the diffractive optical element is configured to generate a one-dimensional beam array. In one embodiment, the diffractive optical element is configured to generate a plurality of Gaussian beams.

[0047] In one embodiment, the diffractive optical element is configured to generate a plurality of beams, each of which has an intensity variance of less than 20% compared to the other beams. In one embodiment, the photodetector includes an upper zone and a lower zone. In one embodiment, the photodetector is a differential array detector.

[0048] In one embodiment, a particle detection system includes an incident beam light source providing an incident beam, a particle monitoring zone disposed in the path of the incident beam and containing particles, a photodetector disposed to detect the incident beam after it leaves the particle monitoring zone, and an excitation beam light source providing an excitation beam directed into the particle monitoring zone. The incident beam, excitation beam, and photodetector may be arranged such that the photodetector detects a combination of light from the incident beam, scattered light due to scattering of the incident beam from particles in the fluid flow in the particle monitoring zone, and scattered light due to scattering of the excitation beam from particles in the fluid flow in the particle monitoring zone.

[0049]

[0049] In one embodiment, a method of particle detection includes the steps of directing an incident beam onto a monitoring zone and a photodetector, directing an excitation beam into the particle monitoring zone, scattering light from the incident beam in the particle monitoring zone, scattering light from the excitation beam in the particle monitoring zone, and detecting a combination of light from the incident beam, scattered light from the incident beam, and scattered light from the excitation beam with the photodetector.

[0050]

[0050] In one embodiment, a method of particle detection includes the steps of directing an incident beam onto a monitoring zone containing a fluid stream having particles and a photodetector, directing an excitation beam into the particle monitoring zone, generating scattered light due to interaction of the incident beam with one or more particles in the particle monitoring zone, generating scattered light due to interaction of the excitation beam with one or more particles in the fluid stream in the particle monitoring zone, and detecting by the photodetector a combination of light from the incident beam or a reference beam, scattered light from the incident beam, and scattered light from the excitation beam.

[0051] In one embodiment, the method may include detecting, by a photodetector, a combination of light from the incident beam, scattered light from the incident beam, and scattered light from the excitation beam.

[0052] In one embodiment, the method may include detecting, with a photodetector, a combination of light from the reference beam, scattered light from the incident beam, and scattered light from the excitation beam.

[0053] In one embodiment, the method may include flowing the particle-containing fluid through a particle monitoring zone, hi one embodiment, the detecting step includes detecting forward scattered light from the incident beam.

[0054] In one embodiment, the method includes emitting a laser beam from a laser and splitting the laser beam into an excitation beam and an incident beam with a polarizing beam splitter. In one embodiment, the method includes generating the incident beam with a first laser and generating the excitation beam with a second laser.

[0055]

[0055] In one embodiment, the method may include a step of generating a particle detection signal by a photodetector, the signal corresponding to the intensity of light from the incident beam combined with scattered light from the incident beam and scattered light from the excitation beam.

[0056]

[0056] In one embodiment, the method includes the steps of guiding an incident beam to a particle, guiding an excitation beam to the particle, scattering light from the incident beam by the particle, scattering light from the excitation beam by the particle, and detecting a combination of light from the incident beam, scattered light from the incident beam, and scattered light from the excitation beam by a photodetector.

[0057] In one embodiment, the method includes diffracting an incident beam into multiple beams by a diffractive optical element. In one embodiment, the photodetector includes an upper zone and a lower zone, and the method includes comparing a signal from the upper zone with a signal from the lower zone. In one embodiment, the method includes increasing a volumetric sampling rate of the fluid flow by the diffracting step.

[0058] In one embodiment, the detecting step includes detecting forward scattered light from the incident beam.

[0059]

[0059] In one embodiment, a method for particle detection includes the steps of generating an incident beam, diffracting the incident beam into multiple beams by a diffractive optical element, directing the multiple beams onto a monitoring zone containing a fluid flow having particles and a photodetector, generating scattered light by interaction of the multiple beams with one or more particles in the fluid flow in the particle monitoring zone, and detecting the scattered light from the multiple beams by the photodetector.

[0060] In one embodiment, the photodetector includes an upper zone and a lower zone, and the method includes comparing a signal from the upper zone with a signal from the lower zone. In one embodiment, the method includes increasing the volumetric sampling rate of the fluid stream by diffraction. In one embodiment, the detecting step includes detecting forward scattered light from the incident beam.

[0061] Without wishing to be bound by any particular theory, beliefs or understandings of underlying principles relating to the devices and methods disclosed herein may be discussed herein, recognizing that an embodiment of the present invention may be operative and useful regardless of whether any mechanistic explanation or hypothesis is ultimately correct. [Brief explanation of the drawings]

[0062] [Figure 1] FIG. 1 is a schematic diagram of a first embodiment of a scattered light interference particle detection system.

[0063] [Figure 2] FIG. 2 shows the characteristic interference pattern signal observed on the incident beam as a particle passes through the beam.

[0064] [Figure 3] FIG. 3 shows a comparison of the detected signals of a double-pass pump beam system, a single-pass pump beam system, and a conventional (non-pump beam) system.

[0065] [Figure 4] FIG. 4 is a diagram illustrating one embodiment of a system for particle detection by scattered light combined with incident light according to the present disclosure.

[0066] [Figure 5A] FIG. 5A shows a 2 micron carrier beam (R to L) with a 5 micron signal pump beam directed into the paper.

[0067] [Figure 6] FIG. 6 is a schematic diagram of a second embodiment of a system for particle detection by scattered light combined with incident light of the present disclosure.

[0068] [Figure 7] FIG. 7 is a schematic diagram of a third embodiment of a system for particle detection by scattered light combined with incident light of the present disclosure, comprising a diffractive element that generates an array of incident beams.

[0069] [Figure 8]

[0069] Figure 8 is a schematic diagram of the diffraction of light by a diffractive optical element.

[0070] [Figure 9] FIG. 9 is a schematic diagram of a one-dimensional beam array generated by the diffractive optical element of FIG.

[0071] [Figure 10] FIG. 10 is a schematic diagram of a fourth embodiment of a system for particle detection by scattered light combined with incident light of the present disclosure, including a dual-path excitation beam.

[0072] [Figure 11] FIG. 11 is a schematic diagram of a fifth embodiment of a system for particle detection by scattered light combined with incident light of the present disclosure, including a collimated excitation beam and incident beam for surface particle detection.

[0073] [Figure 12] 12 is a schematic diagram of a sixth embodiment of a system for particle detection by scattered light combined with incident light of the present disclosure, including a dual-path incident beam configuration.

[0074] In the following description, numerous specific details are set forth regarding the devices, device components, and methods of the present invention in order to fully explain the precise nature of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details.

[0075] Generally, the terms and phrases used herein have their art-recognized meanings, which can be found by reference to standard texts, journal literature, and contexts understood by those skilled in the art. The following definitions are provided to clarify their specific application in the context of the present invention.

[0076]

[0076] "Particle" refers to a small object often considered a contaminant. A particle can be any substance generated by the action of friction, for example, when two surfaces are in mechanical contact and mechanically actuated. A particle can comprise materials such as dust, pollution, smoke, ash, water, soot, metals, oxides, ceramics, minerals, any combination thereof, or aggregates of other materials or contaminants. "Particle" can also refer to biological particles, such as viruses, spores, and microorganisms, including bacteria, fungi, archaea, protists, and other single-celled microorganisms. In some embodiments, for example, biological particles are characterized by size dimensions (e.g., effective diameters) ranging from 0.1 to 15 μm, and optionally, for some applications, from 0.5 to 5 μm. A particle can refer to a small object that can absorb, emit, or scatter light and thus be detectable by an optical particle counter. As used herein, the term "particle" refers to the exclusion of individual atoms or molecules of a carrier fluid (e.g., water, air, process liquid chemicals, process gases, etc.). In some embodiments, the particles may initially reside on a surface, such as a tool surface of a microfabrication facility, and may be analyzed in the fluid after being released from the surface. Some systems and methods are capable of detecting particles, including aggregates of material, having a size dimension, such as an effective diameter, greater than 5 nm, greater than 10 nm, greater than 20 nm, greater than 30 nm, greater than 50 nm, greater than 100 nm, greater than 500 nm, greater than 1 μm, or greater than 10 μm. Some embodiments of the invention are capable of detecting particles having a size dimension, such as an effective diameter, selected from the range of 10 nm to 150 μm, optionally in some applications from 10 nm to 10 μm, optionally in some applications from 10 nm to 1 μm, and optionally in some applications from 10 nm to 0.5 μm.

[0077] The phrase "detecting a particle" broadly refers to the detection, identification of the presence or absence, counting, and / or characterization of particles (e.g., characterizing particles with respect to size dimensions such as effective diameter). In some embodiments, detecting particles refers to counting particles. In some embodiments, detecting particles refers to the characterization and / or measurement of physical properties of particles, such as effective diameter, cross-sectional dimension, shape, size, aerodynamic size, or any combination thereof. In some embodiments, detecting particles is performed in a fluid stream, such as a gas, having a volumetric flow rate selected from the range of 0.05 CFM to 10 CFM, optionally in some applications from 0.1 CFM to 5 CFM, and optionally in some applications from 0.5 CFM to 2 CFM. In some embodiments, detecting particles is performed in a fluid stream, such as a liquid, having a volumetric flow rate selected from the range of 1 to 1000 mL / min.

[0078] The terms "optical particle counter" or "particle counter" are used interchangeably to refer to a particle detection system that detects particles by optical detection, typically by analyzing particles in a fluid stream. Optical particle counters include liquid particle counters and aerosol particle counters (e.g., systems capable of detecting individual single particles in a fluid stream). Optical particle counters deliver a beam of electromagnetic radiation (e.g., a laser) to an analysis area, where the beam interacts with any particles and then detects the particles based on scattered, emitted, or transmitted light from a flow cell. Detection may focus on electromagnetic radiation scattered, absorbed, blocked, and / or emitted by the particle(s). Various detectors for optical particle counters are known in the art, including single detector elements (e.g., photodiodes, photomultiplier tubes, etc.), detector arrays, cameras, various detector orientations, etc. Optical particle counters include condensation particle counters, condensation nuclei counters, split-beam differential systems, and the like. When used in the context of a condensation particle counter, the particle counter portion refers to the detection system (e.g., electromagnetic radiation source, optics, filters, collector, detector, processor, etc.). In one embodiment, for example, an optical particle counter includes an electromagnetic radiation beam generating source and beam steering and / or shaping optics that direct and focus the beam into a region where a fluid sample flows (e.g., a liquid or gas flows through a flow cell). A typical optical particle counter consists of a photodetector, such as an optical detector array, in optical communication with the flow cell and collection optics that collect and image electromagnetic radiation scattered, transmitted, or emitted by particles passing through the beam. The particle counter may further include electronics and / or processor components for readout, signal processing, and analysis of the electrical signal generated by the photodetector, such as a current-to-voltage converter, a pulse height analyzer, and signal filtering and amplification electronics. The optical particle counter may also include a fluid actuation system, such as a pump, fan, or blower, for generating a flow (e.g., generating a flow characterized by a volumetric flow rate) that transports the particle-containing fluid sample to a detection region of the flow cell.Useful flow rates for samples containing one or more gases include flow rates selected from the range of 0.05 CFM to 10 CFM, optionally in some applications 0.1 CFM to 5 CFM, and optionally in some applications 0.5 CFM to 2 CFM. Useful flow rates for samples containing one or more liquids include flow rates selected from the range of 1 to 1000 mL / min.

[0079] The phrase "interferometric detection of particles" refers to systems and methods for detecting one or more particles by optical interference. In some embodiments, the superposition of coherent beams of electromagnetic radiation produces optical interference for detecting, counting, and / or determining size characteristics of particles that interact with at least a portion of the electromagnetic radiation.

[0080]

[0080] As used herein, "structured beam interferometric detection" refers to an interferometric system and method in which a structured probe beam of electromagnetic radiation having a non-Gaussian intensity distribution is passed through a particle-containing flow cell and detected by an optical detector array that detects, counts, and / or characterizes the particles.

[0081] As used herein, "homodyne interferometric detection" refers to an interferometric system and method in which an incident beam passes through a flow cell, where it interacts with particles, thereby scattering light that is collected and combined with a reference beam that is not frequency-shifted relative to the incident beam, and the combined light is measured by a detector. In some embodiments, the disclosed systems are configured to provide excitation homodyne interferometric detection, where an excitation beam intersects with the incident beam at a particle monitoring zone, such that particles interact with both beams and the resulting scattered light from both beams is combined with the non-frequency-shifted reference beam. Thus, excitation homodyne interferometric detection can increase the scattered light component of the combined light measured by the detector.

[0082] As used herein, "self-homodyne interferometric detection" refers to an interferometric system and method in which an incident beam interacts with particles as it passes through a flow cell, scattering light that is generated and combined with the incident beam. In some embodiments, the disclosed systems are configured to provide excitation self-homodyne interferometric detection, where an excitation beam intersects with the incident beam at a particle monitoring zone, allowing particles to interact with both beams and resulting scattered light from both beams to be combined with the incident beam. Thus, excitation self-homodyne interferometric detection can increase the scattered light component of the combined light measured by the detector.

[0083] As used herein, the term "heterodyne interferometric detection" refers to an interferometric system and method in which an incident beam interacts with particles as it passes through a flow cell, scattering light that is collected and measured by a detector and combined with a frequency-shifted reference signal relative to the incident beam. In some embodiments, the disclosed systems are configured to provide excitation heterodyne interferometric detection, where an excitation beam intersects with the incident beam at a particle monitoring zone, allowing particles to interact with both beams and the resulting scattered light from both beams to be combined with the frequency-shifted reference signal. Thus, excitation heterodyne interferometric detection can increase the scattered light component of the combined light measured by the detector.

[0084]

[0084] Represents an interferometric system and method in which a reference beam is frequency shifted, typically using a lock-in amplifier in conjunction with an optical detector, a beam of coherent electromagnetic radiation is passed through a flow cell and combined with a separate reference beam, and the combined beam is detected by an optical detector array that detects, counts, and / or characterizes particles. In some embodiments, the particle counter is configured to provide heterodyne interferometric detection of said particles by collecting off-axis scattered light and combining the off-axis scattered light with the reference beam to generate an interference signal.

[0085] As used herein, the phrase "differential detection" refers to techniques and systems that use differential signals from one or more forward, on-axis detector pairs, for example, at scattering angles within 0.5° of the optical axis of the incident beam, optionally within 0.1° of the optical axis of the incident beam in some applications, and optionally at or near 0°. A single pixel pair for differential detection can be configured by using at least two pixels (e.g., one upper (or top) and one lower (or bottom)) to generate the differential signal. Alternatively, multiple pixels can be employed for each active detector area (e.g., upper and lower active areas) of a differential detector, such as a segmented differential detector that uses multiple pixel pairs by including one or more pixel pairs, e.g., one pixel of each pixel pair corresponds to the upper active detector area and the other pixel of each pixel pair corresponds to the lower active area. The number of pixel pairs can range, for example, from 1 to 500 pixels, and optionally, in some applications, from 50 to 100 pixels. In some embodiments, a differential signal is generated by differentially summing signals from pairs of pixels corresponding to different active areas of a segmented detector array, such as the top and bottom halves. The use of differential detection in the present systems and methods allows for reduced noise and therefore improved signal-to-noise ratios. In some embodiments, differential detection is used, for example, to detect a combination of incident electromagnetic radiation transmitted through the flow cell and electromagnetic radiation forward scattered by one or more particles in the fluid flow in the flow cell. In some embodiments, the distribution of incident light has a balanced power distribution between the first and second active detection areas (e.g., the top and bottom halves) of the differential detector, such that the incident radiation powers of the first and second active detection areas are characterized by a difference of, for example, within 10%, optionally within 5% in some applications, and optionally within 1% in some applications. Differential detection includes techniques and systems with closed-loop control based, for example, on an evaluation of the noise amplitude of the differential signal in the absence of particles (i.e., no scattering from particles).In some embodiments, the use of steering mirrors adjusts the position of the incident beam on the detector to reduce or minimize the noise level of the differential signal, which can occur when the beam power is split evenly between the first and second active detector elements (e.g., the upper and lower elements of the detector). Closed-loop control can also be achieved by aligning the beam with the detector axis through detector position translation and detector rotation to reduce or minimize the noise level of the differential signal.

[0086] Detecting and counting small particles (e.g., those with an effective diameter less than 100 nm) in clean and ultra-clean fluids to provide statistically significant data requires a high signal-to-noise ratio (S / N). A high S / N ratio allows for clear detection of nanoparticles above the noise floor. As used herein, "statistically significant data" refers to the detection of enough particles per unit time to allow accurate assessment of the contamination level in the fluid. In some embodiments, a high S / N ratio does not directly correlate to sizing accuracy. For example, in some optical particle counters, the beam waist occupies only a small portion of the flow cell channel, and the technique monitors only a portion of the total flow, so particles may pass through the edge of the beam, where irradiance is lower than in the center. A 50 nm particle passing through the outer edge of the beam may generate a signal similar to that generated by a 10 nm particle passing through the center of the beam. Thus, while some optical particle counters can detect 2 nm particles with a high S / N ratio, sizing accuracy is not as high. A goal of the present optical particle counter and method is to be able to count enough particles in a short time to quantitatively and statistically accurately assess the contaminant level in an ultrapure fluid. For example, current prior art particle counters may require up to 40 minutes to count enough particles to measure a statistically relevant concentration (acceptable relative standard deviation) when monitoring a prior art ultrapure water system. By improving and maintaining a high S / N ratio using the present system and method, the time interval required to measure this statistically acceptable minimum particle count can be reduced by more than 10 times. This is beneficial because it allows users to more quickly identify deviations from process control limits.

[0087] The phrase "high signal-to-noise ratio" refers to a signal-to-noise ratio of an optical particle detection system that is sufficient for accurate and sensitive detection of particles in a fluid stream containing particles characterized by small physical dimensions (e.g., effective diameters of 200 nm or less, optionally in some embodiments 100 nm or less, and optionally in some embodiments 50 nm or less). In one embodiment, "high signal-to-noise ratio" refers to a signal-to-noise ratio that is high enough to detect particles characterized by small physical dimensions, such as particles with effective diameters as small as 20 nm, optionally in some applications 10 nm, and optionally in some applications 1 nm. In one embodiment, "high signal-to-noise ratio" refers to a signal-to-noise ratio that is high enough to accurately detect and count particles with a false positive rate of 50 particles / L or less, for example, for the detection of particles selected from the range of 1-1000 nm in effective diameter. In one embodiment, "high signal-to-noise ratio" refers to a signal-to-noise ratio that is high enough to provide a statistically acceptable minimum particle count in a time frame that is at least 10 times shorter than conventional optical particle counters.

[0088] The phrase "significant performance degradation of the particle counting process" refers to a decrease in the ability of a particle detection system to detect and count particles in a fluid stream. In some embodiments, a significant performance degradation of the particle counting process refers to a 20% or greater shift in the detection threshold voltage for the smallest size channel. In some embodiments, a significant performance degradation of the particle counting process refers to an increase in the false count rate of 50 particles / L or greater. In some embodiments, a significant performance degradation of the particle counting process refers to an increase in the time required to provide a statistically acceptable minimum particle count of 5 times or greater, and optionally in some embodiments, 10 times or greater. In some embodiments, a significant performance degradation of the particle counting process, for example, as a result of poor control of noise sources, refers to a decrease in signal-to-noise ratio, resulting in poor detectability of the smallest particles. For example, a decrease in signal-to-noise ratio causes the detected signal from a 50 nm particle to look like a 20 nm particle, making the signal of a 20 nm particle indistinguishable from noise, resulting in decreased detectability and resulting in fewer particle counts per unit time and / or false counts due to increased noise levels.

[0089] As used herein, "structured beam" refers to a coherent beam of electromagnetic radiation (e.g., a laser) having a non-Gaussian spatial intensity distribution. Structured beams include beams characterized by regions of attenuation such as dark beams, beams with line foci having dark line singularities, beams characterized by two or more discrete intensity lobes, etc. Structured beams include focused synthetic laser beams. Structured beams can be generated by techniques known in the art, such as the use of optical masks, modification of laser cavities, combining multiple beams, spatial and / or polarization filters, and other manipulations such as in interference or polarization modification schemes.

[0090] As used herein, the term "dark beam" refers to a laser beam with a central dark spot or dark line singularity, typically a Gaussian envelope. The primary advantage of this beam for PSA (particle size analysis) purposes comes from the fact that the central dark spot / line is narrower than a conventional Gaussian spot and has the same divergence. This allows for greater sensitivity to the location and structure of interfering objects while maintaining the sufficient volume of a Gaussian beam for concentration measurements and large particle interactions. Dark beams can be generated by transforming a conventional laser beam with an optical element (typically a diffractive element) or by specially designing a laser resonator to emit a dark beam. Useful methods for generating dark beams include those described by R. Piestun and J. Shamir, "Synthesis of three-dimensional light-fields and applications," Proc. IEEE, Vol. 90(2), pp. 220-244, (2002). These laser modes are typically members of sets known as Gauss-Laguerre and Gauss-Hermite modes.

[0091] As used herein, "dual-pass" refers to a configuration in which a beam is directed to a monitoring zone a first time, then reflected back (e.g., via a mirror), and then directed to the monitoring zone a second time. When the monitoring zone includes a flow cell or cuvette, dual-pass refers to a configuration in which the beam passes through the flow cell or cuvette once, then reflected back through the flow cell or cuvette (e.g., via a mirror). When the monitoring zone includes a surface for particle monitoring, dual-pass refers to a configuration in which the beam is directed to the surface once, reflected back from the surface, and then reflected back from the surface (e.g., via a mirror). Utilizing a dual-pass configuration allows the light beam to interact with the same particle in the particle monitoring zone twice. Thus, a dual-pass configuration can increase the sensitivity of a particle detection system by increasing the amount of light scattered by the particle.

[0092] As used herein, "multi-pass" refers to a configuration in which the beam is directed to a monitoring zone a first time, reflected back (e.g., via a mirror), then directed to the monitoring zone a second time, then directed back to the monitoring zone a third time (e.g., via a semi-transparent mirror), and so on. When the monitoring zone includes a flow cell or cuvette, multi-pass refers to a configuration in which the beam passes through the flow cell or cuvette once, reflected back (e.g., via a mirror) through the flow cell or cuvette, then directed back to the monitoring zone a third time (e.g., via a semi-transparent mirror), and so on. When the monitoring zone includes a surface for particle monitoring, multi-pass refers to a configuration in which the beam is directed to the surface once, reflected back from the surface, reflected back from the surface (e.g., via a mirror), reflected back from the surface a second time, then directed back to the monitoring zone a third time (e.g., via a semi-transparent mirror), and so on. Using a multi-pass configuration, the light beam can interact with the same particle in the particle monitoring zone multiple times. Thus, a multi-path configuration can increase the sensitivity of a particle detection system by increasing the amount of light scattered by the particle.

[0093] As used herein, "beam propagation axis" refers to the axis parallel to the direction of travel of a beam of electromagnetic radiation.

[0094] As used herein, "optical communication" refers to components arranged so that light can travel between them.

[0095] As used herein, "optical axis" refers to the direction in which electromagnetic radiation propagates through a system.

[0096] As used herein, the term "optical detector array" refers to an optical detector capable of spatially resolving an input signal (e.g., electromagnetic radiation) two-dimensionally across its active area. The optical detector array is capable of generating an image (e.g., an image corresponding to an intensity pattern on the active area of the detector). In one embodiment, the optical detector array includes an array of individual detector elements, also referred to herein as pixels, such as a two-dimensional array of photodetectors, charge-coupled device (CCD) detectors, complementary metal-oxide semiconductor (CMOS) detectors, metal-oxide semiconductor (MOS) detectors, active pixel sensors, microchannel plate detectors, or a two-dimensional array of photodiodes.

[0097] As used herein, a "light source" refers to a device or device component capable of delivering electromagnetic radiation to a sample. This term is used broadly to include any electromagnetic radiation, such as visible, ultraviolet, and / or infrared radiation, and is not limited to visible radiation, such as a visible light beam. The light source may be embodied as a laser or laser array, such as a diode laser, a diode laser array, a diode-pumped solid-state laser, an LED, an LED array, a gas-phase laser, or a solid-state laser, to name a few.

[0098] As used herein, the terms "electromagnetic radiation" and "light" are used synonymously herein and refer to waves in the electromagnetic field. Electromagnetic radiation useful in the methods of the present invention includes, but is not limited to, ultraviolet light, visible light, infrared light, or any combination thereof having a wavelength from approximately 100 nanometers to approximately 15 microns.

[0099] As used herein, the term "incident beam" refers to a light beam (eg, a laser beam) that is incident on a photodetector.

[0100] As used herein, the term "particle interrogation zone" refers to a zone of a particle detection system where one or more particles interact with an incident beam and / or an excitation beam, scattering light. In some embodiments, the particle monitoring zone may comprise a cuvette and / or flow cell that confines a particle-laden liquid flowing therethrough. In other embodiments, an unconfined particle-laden gas jet may flow through the particle monitoring zone. In some embodiments, the particle monitoring zone may comprise a surface on which particles are monitored.

[0101] As used herein, the term "pump beam" refers to a light beam (eg, a laser beam) configured to increase the scattered light component of the light detected by a photodetector.

[0102] As used herein, the term "reference beam" refers to a light beam that does not interact with the particle to be detected and, optionally, generates optical interference by being in phase with another source of electromagnetic radiation.

[0103] In the following description, numerous specific details are set forth regarding the devices, device components, and methods of the present invention in order to fully explain the precise nature of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details.

[0104]

[0104] The particle detection signal measured on-axis as a particle passes through a focused laser beam is believed to originate from the interference pattern produced when the forward scattered light interacts with the incident (carrier) beam. In this case, the Van Cittert-Zernike theorem applies to the collected scattered light when the particle is located at the blur spot and focal depth of the collection optics. Different angular values of the scattered field within the blur spot may not be resolvable due to the limitations of the collection optics. Therefore, the scattered light is imaged into a plane wave that is coincident with the incident field and is parallel and in phase. The scattered light collected within the blur spot is coherent.

[0105]

[0105] As a result, it becomes possible to detect the interference between the scattered light and the incident light, and the amplitude of the signal is proportional to the product of the scattered intensity and the incident intensity.

[0106] When two plane waves are combined, the electric field E observed at the detector is d is as follows: E d =E c +E s where E c is the electric field of the carriers, and E s is the electric field of the scattered light coincident with the carrier. The intensity at the detector is: I d = εcE d 2 =εc(E c +E s ) 2 =εc(E c 2 +E s 2 +2E c E s ) where ε is the dielectric constant of the medium and c is the speed of light. c 2 is essentially constant for small particle interactions. E s 2 fluctuates when small particles interact with the carrier beam, but the amplitude is very small. The important term is called the interference term, 2Ec E s , and small particles passing through the beam cause relatively large fluctuations in intensity at the detector, resulting in interference. The amplitude of the interference signal is 2E c E s cosδ, where δ is the phase difference between the two waves. This phase difference varies with the path length difference between the scattered light and the incident (carrier) beam as the particle passes through the excitation beam.

[0107]

[0107] Thus, the detected signal can be increased by increasing the incident beam intensity and / or the scattered light intensity on the detector. The incident beam intensity has an upper limit at the saturation point of the detector / electronics. Increasing the incident power not only increases the signal amplitude but also increases the shot noise of the detector. However, because the scattered intensity affects the magnitude of the transient detected signal but has little effect on the overall beam power on the detector, there is effectively no upper limit to the acceptable scattered intensity. Increasing the scattered intensity increases the detected signal without measurably increasing the noise. The scattered intensity can be excited, for example, by a second beam that can be orthogonal to the incident beam (see Figure 1). The scattered intensity can be excited by forward or side scatter. It has been found that the collected scattered intensity is coherent and parallel to the incident low-power beam as long as the phase is essentially the same (for maximum signal, it actually fluctuates with a DC background, creating an AC signal) and the scattering event occurs within a blur spot. This can lead to interference that can be detected by the detector.

[0108] The utility and advantages of this scattering intensity excitation include increased particle detection signal without increased noise. Systems employing this method are more scalable than other systems. Furthermore, the signal is generated in situ and directly integrated into the incident beam. In some embodiments, the systems and methods disclosed herein enable the generation of stable interference signals by reducing or eliminating noise and / or thermal expansion issues, as well as z-axis alignment issues.

[0109]

[0109] Additionally, the systems and methods disclosed herein may benefit from laser noise reduction with differential photodetectors. The systems and methods disclosed herein may be adapted for use in measuring particles in liquids, gases, and on surfaces.

[0110]

[0110] The present invention can be better understood by the following non-limiting examples.

[0111] Example 1: Single-path excitation beam nanoparticle detection

[0112]

[0112] Referring now to Figure 1, this figure shows an example of a single-path excitation beam particle detection system. The illustrated system includes a light source 1, an isolator 2, a phase mask 3, multiple half-wave plates 4, two polarizing beam splitters, multiple mirrors 6, a pair of microscope objectives 7, a flow cell 9, a digital microscope 10, and a photodetector 11. As shown, the light source 1 generates a light beam that passes through the isolator 2, the phase mask 4, and the half-wave plates 4. The beam is then split by the polarizing beam splitter 5 into an incident beam (labeled the carrier beam) and an orthogonal signal excitation beam. The incident beam is sent to another half-wave plate 4, a first microscope objective 7, and a monitoring zone (flow cell 9). After passing through the flow cell 9, the incident beam passes through the second microscope objective 7 and is finally directed onto the photodetector. After being split from the incident beam by the first polarizing beam splitter, the excitation beam is sent perpendicular to the incident beam through a half-wave plate 4, a polarizing beam splitter 5, another half-wave plate 4, a microscope objective 8, and a flow cell 9. After passing through the flow cell 9, the excitation beam is directed to a digital microscope. The flow cell 9 may contain a fluid, such as air or water, containing suspended particles. As particles pass through the flow cell 9, light from both the incident beam and the excitation beam may be scattered by the particles. Thus, the light from the incident beam may combine with forward scattered light due to the incident beam / particle interaction and side scattered light due to the excitation beam / particle interaction. The optical configuration, particularly the half-wave plate and polarizing beam splitter, ensures that the light from these three light sources is sufficiently phase-coincident and can be combined and detected by a photodetector 11.

[0113] In the illustrated embodiment, a 50x microscope objective 7 is used to generate a single-pass incident beam with a waist of approximately 2 μm and a depth of field of approximately 7 μm. A second 50x objective 7 is used as the focusing optics, defining a blurred spot where particle / beam interactions generate a signal. A low-power (30 mW at the detector) beam is used in a single-pass detection setup, while a second, high-power excitation beam (single laser source) is introduced into the flow cell, oriented perpendicular to the propagation of the low-power beam toward the detector. The high-power beam (approximately 3.5 W) is focused by a 10x objective, resulting in a beam waist diameter of approximately 10-12 μm and a depth of field of approximately 300 μm (potential for interaction with the high-aspect ratio, low-power beam). Alternatively, a 20x objective is used to focus the high-power beam, resulting in a beam waist diameter of approximately 5-6 μm and a depth of focus of approximately 45 microns.

[0114] Example 2: Excitation beam positioned opposite to the incident beam in the monitoring zone

[0115]

[0115] Referring now to Figure 6, in one embodiment, the excitation beam may intersect the particle monitoring zone in the opposite direction to the incident beam. As shown, the beam may be split into the incident and excitation beams using a polarizing beam splitter. The incident beam may be directed by mirrors (M1, M2) through a quarter-wave plate to the flow cell and another quarter-wave plate. The excitation beam may be directed by M3 in the opposite direction to the incident beam through the same two quarter-wave plates on either side of the flow cell. Thus, the incident beam, forward-scattered light from the incident beam, and back-scattered light from the excitation beam may all be combined and focused onto the photodetector array.

[0116] Example 3: Beam Array

[0117]

[0117] Referring now to Figures 7-9, in one embodiment, the volumetric sampling rate of a particle monitoring system may be increased through the use of a diffractive optical element. Figure 7 shows an example. As shown, the particle monitoring system includes a diffractive optical element 12 in the optical path of an incident beam. The diffractive optical element 12 functions to generate an array of beams. Figure 8 is a schematic diagram of the effect of a diffractive optical element on a light beam. As the light travels from left to right, the diffractive optical element located at the left edge of the diagram diffracts the light into five beams, in this case of essentially equal intensity.

[0118]

[0118] The multiple beams are directed into a flow cell containing the particles. The waists of each beam are then imaged onto a pair of detector elements, one above the other. Figure 9 shows a one-dimensional beam array created from a diffractive optical element. By directing the beam array into the fluid stream to be sampled by the beam, the volume of the fluid stream that can be sampled is increased compared to a single beam alone.

[0119] In this example, a 2 x 100 element array is used, but any multi-element array can be used as long as there is an upper and lower element. Differential detection may be used, whereby signals from the upper and lower detector elements are compared and analyzed.

[0120]

[0120] Furthermore, diffractive optical elements can be used with Gaussian beams to generate Gaussian beam arrays, and with structured beams such as dark beams to generate dark beam arrays.

[0121] Example 4: Particle detection with a dual-path excitation beam

[0122] 10, in one embodiment, the excitation beam may be arranged in a dual-pass configuration. As shown, the excitation beam passes through flow cell 9, then microscope objective 8, where it is reflected off mirror 6 and directed back toward microscope objective 8 and flow cell 9. This allows particles passing through the flow cell to scatter light from the excitation beam once as it passes through the flow cell for the first time, and then again as it is reflected and passes through the flow cell for the second time. Thus, the amplitude of the signal generated by the photodetector in response to a particle passing through the particle monitoring zone may be significantly greater than in a single-pass excitation beam configuration.

[0123]

[0123] It should be noted that, as an alternative or in addition to a dual-path excitation beam, the incident beam may be configured as a dual-path beam.

[0124] Example 5: Comparison of nanoparticle detection with a dual-pass excitation beam, a single-pass excitation beam, and conventional techniques (no excitation beam)

[0125] The net effect of the nanoparticle detection improvement achieved by excitation interferometry is twofold. A comparison of the range of excitation and non-excitation data along the amplitude axis in Figure 3 reveals a significantly increased amplitude of the detected signal. In the experiment of Figure 3, monodisperse particles were fed into a dual-pass excitation beam particle detector (similar to Figure 10), a single-pass excitation beam particle detector (similar to Figure 1), and a conventional particle detector without beam excitation. The area under each curve represents the number of particles detected per minute. As shown, the single-excitation and dual-excitation configurations are capable of detecting more particles per time than non-excitation measurements. This is due to increased detection sensitivity and improved detection of particles passing near, but not through, the incident beam. Particles passing through the large excitation beam near the incident beam can generate scattered light, resulting in a signal in the incident beam. This effectively increases the volume of fluid detected per unit time relative to the non-excitation incident beam.

[0126] Example 6: Collimated beam for surface detection

[0127] 11, in one embodiment, the excitation beam 104 and the incident beam 105 may have parallel propagation axes as they approach the monitoring zone (in this case, surface 101). Both beams may pass through a converging lens 102 having an axis 103 parallel to the propagation axes of both beams 104, 105 just before reaching the monitoring zone 101. The surface 101 may be disposed at the focal point of the two beams. Thus, particles on the surface 101 may scatter light from both beams 104, 105. In some embodiments, a system employing the parallel beam configuration of FIG. 11 may include a quarter-wave plate and a polarizing beam splitter. Both beams may pass through the polarizing beam splitter, the quarter-wave plate, and the objective lens before interacting with the particle a first time, reflecting off the surface and interacting with the particle a second time, then passing through the objective lens and the quarter-wave plate again, with the polarizing beam splitter deflecting the guiding direction of the incident beam by 90°. This allows the polarization of the returning beam to be orthogonal to the original beam as a result of passing through the quarter wave plate twice.

[0128] Example 7: Excitation interference beam

[0129] In one embodiment, a calcite beam can generate two parallel beams with opposite polarizations. One beam can be a low-power incident beam and the second beam a high-power excitation beam. One of the beams can pass through a half-wave plate to match the polarization before passing through a positive lens that focuses the beam to a common focal point in a particle monitoring zone, which can be on a surface, in a gaseous fluid, or in a liquid fluid. After passing through the focal point where the particles can interact, the two beams can diverge and be re-collimated by another lens. A mirror or knife-edge prism then directs the excitation beam in a different direction from the incident beam (to a beam dump), and the incident beam is sent to a differential photodetector.

[0130] Example 8: Low-power laser embodiment

[0131] In some embodiments, the system may be able to function over a wide range of laser powers by using various photodetector technologies. For example, in some embodiments, the photodetector may comprise a silicon PIN photodiode, and the laser power at the detector may range from 5 to 50 mW for an incident excitation beam of 500 to 10,000 mW. In alternative embodiments, the photodetector may comprise a more sensitive avalanche photodiode, and the laser power at the detector may range from 0.001 to 0.01 mW for an incident excitation beam of 0.1 to 200 mW. In some embodiments, the use of a photomultiplier tube detector may further reduce the laser power. The ability to perform nanoparticle detection using lower power lasers allows for lower cost and smaller instrumentation and eliminates the need for actively cooled lasers.

[0132] Example 9: Double-pass incident beam

[0133]

[0133] Referring now to Figure 12, this figure shows one embodiment of a particle detection system configured with a dual-path incident beam. An incident light beam (e.g., a laser) may be generated by a light source 51. The incident beam may pass through an isolator 52 and then a beam expander 53. The incident beam may then be reflected by a mirror 54 and (optionally) a phase mask 55. The incident beam may then pass through a half-wave plate 56 and be reflected by a mirror 57. The incident beam may then pass through a polarizing beam splitter 62 and a quarter-wave plate 64. The incident beam may then pass through an objective lens 58 and a cuvette 59. The cuvette 59 may contain a particle-containing fluid. Thus, as the incident beam passes through the cuvette 59, it may interact with particles, scattering light. The incident beam, together with the forward scattered light from the particle / beam interaction, then passes through collection optics 60, reflects off mirror 63, and makes a second pass through optics 60 and cuvette 59 in the opposite direction. Thus, the incident beam can interact with the particle a second time (given the speed of light relative to the velocity of the fluid through the cuvette, the particle will still be considered to be at essentially the same location within the cuvette as it was during the first particle / beam interaction). An excitation beam (not shown) may also pass through cuvette 59, e.g., orthogonal to the incident beam (out of the page). This allows the incident beam to be combined with the forward scattered light from both particle / incident beam interactions, as well as the side scattered light from the particle's interaction with the excitation beam. This combination of light may then pass through objective lens 58, quarter-wave plate 64, and finally be guided onto detector 61 by polarizing beam splitter 62. [Statement of Incorporation and Modifications]

[0134]

[0134] All references throughout this application (e.g., patent documents, including issued or patented patents or equivalents, published patent applications, and source materials such as non-patent documents) are incorporated herein in their entirety as if individually incorporated, to the extent that each reference is at least partially consistent with the disclosure of this application (e.g., a partially contradictory reference is incorporated except for the partially contradictory portion).

[0135] The terms and expressions employed herein are used as terms of description and not of limitation in any way, and the use of such terms and expressions is not intended to exclude any equivalents of the features shown and described, or portions thereof, while recognizing that various modifications are possible within the scope of the claims of the present invention. Therefore, while the present invention has been specifically disclosed in terms of preferred embodiments, exemplary embodiments, and optional features, it is understood that improvements and modifications of the concepts disclosed herein may be made by those skilled in the art, and that such improvements and modifications are considered to be within the scope of the present invention as defined by the appended claims. The specific embodiments described herein are examples of useful embodiments of the present invention, and it will be apparent to those skilled in the art that the present invention can be practiced using many variations of the apparatus, apparatus components, and method steps described herein. It will be apparent to those skilled in the art that the methods and apparatus useful therefor may include many optional configurations, processing elements, and steps.

[0136] As used herein, in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, a reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art. The terms "a" (or "an"), "one or more," and "at least one" may be used interchangeably herein. The terms "comprising," "including," and "having" may be used interchangeably. The phrase "of any of claims XX-YY" (where XX and YY represent claim number) is intended to provide an alternative form of multiple dependent claiming, and in some embodiments may be used interchangeably with the phrase "as in any one of claims XX-YY."

[0137]

[0137] Any device, system, process, combination of components, or method described or illustrated herein can be used to practice the present invention, unless otherwise specified.

[0138]

[0138] Whenever a range (e.g., a temperature range, a time range, a composition range, or a concentration range) is given herein, all intermediate ranges and subranges, as well as all individual values within the given range, are intended to be included in the disclosure. It is understood that any subranges included in the description herein, and any individual values within a range or subrange, may be excluded from the claims.

[0139] All patents and publications cited herein are indicative of the level of skill of those skilled in the art to which this invention pertains. The references cited herein are hereby incorporated by reference in their entirety to indicate the prior art as of their respective publication or filing dates, and this information may be incorporated herein, if necessary, to exclude specific embodiments in the prior art. For example, when claiming a composition of matter, it is understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not included in the claimed composition of matter.

[0140] As used herein, "comprising" is synonymous with "including," "containing," or "characterized by," and is inclusive, i.e., open-ended, and thus does not exclude additional, unrecited elements or method steps. As used herein, "consisting of" excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of" does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In all instances herein, the terms "comprising," "consisting essentially of," and "consisting of" are each interchangeable with either of the other two terms. The invention illustratively described herein can be suitably practiced in the absence of any element(s), limitation(ies), not specifically disclosed herein.

[0141] Those skilled in the art will appreciate that starting materials, biological materials, reagents, synthetic methods, purification methods, analytical methods, testing methods, and biological methods not specifically exemplified can be adapted to practice the present invention without undue experimentation. All functional equivalents known in the art of any such materials and methods are intended to be encompassed by this invention. The terms and expressions employed are used as terms of description and not of limitation in any way, and no exclusion of any equivalents of the features shown and described or portions thereof is intended by the use of such terms and expressions. However, it is recognized that various modifications are possible within the scope of the claims of this invention. Thus, while the present invention has been specifically disclosed in terms of preferred embodiments and optional features, it is to be understood that improvements and modifications of the concepts disclosed herein may occur to those skilled in the art, and that such improvements and modifications are considered to be within the scope of the present invention as defined by the appended claims. [Item of invention] [Item 1] an incident beam light source for providing an incident beam; a particle monitoring zone disposed in the path of the incident beam and containing particles; a photodetector disposed to detect the incident beam after it leaves the particle monitoring zone; an excitation beam source providing an excitation beam directed into the particle monitoring zone; Equipped with The photodetector light from the incident beam or reference beam; scattered light resulting from scattering of the incident beam from the particles in the fluid stream in the particle monitoring zone; scattered light due to scattering of the excitation beam from the particles in the fluid stream in the particle monitoring zone; the incident beam, the excitation beam, and the photodetector are arranged to detect a combination of: [Item 2] Item 10. The particle detection system of item 1, wherein the incident beam intersects the excitation beam at the monitoring zone. [Item 3] 3. The particle detection system of claim 1, wherein the incident beam, the excitation beam, and the photodetector are arranged such that the photodetector detects a combination of light from the incident beam, scattered light due to scattering of the incident beam off the particles in the particle monitoring zone, and scattered light due to scattering of the excitation beam off the particles. [Item 4] 4. The particle detection system according to claim 1, wherein the incident beam, the excitation beam, and the photodetector are arranged so that the photodetector detects a combination of light from the reference beam, scattered light resulting from scattering of the incident beam from the particles in the particle monitoring zone, and scattered light resulting from scattering of the excitation beam from the particles. [Item 5] Item 5. The particle detection system of item 4, wherein the reference beam is a homodyne interferometric reference beam. [Item 6] Item 5. The particle detection system of item 4, wherein the reference beam is a heterodyne interferometric reference beam. [Item 7] 7. The particle detection system according to any one of items 1 to 6, wherein the scattered light resulting from scattering of the incident beam in the particle monitoring zone is forward scattered light. [Item 8] the incident beam is polarized before entering the surveillance zone; the excitation beam is polarized before entering the monitoring zone; 8. The particle detection system of claim 1, wherein the incident beam and the excitation beam are configured such that the polarization axis of the incident beam is within 5° of the polarization axis of the excitation beam in the monitoring zone. [Item 9] 9. The particle detection system according to any one of items 1 to 8, wherein in the photodetector, the polarization axes of the scattered light due to scattering of the incident beam, the scattered light due to scattering of the excitation beam, and the light from the incident beam are within 5° of each other. [Item 10] a laser and a polarizing beam splitter; the incident beam light source includes light from the laser guided on a first optical path through the polarizing beam splitter; 10. The particle detection system of any one of items 1 to 9, wherein the excitation beam light source includes light from the laser guided on a second optical path via the polarizing beam splitter. [Item 11] a first laser and a second laser; the incident beam light source includes light from the first laser; 11. The particle detection system according to any one of items 1 to 10, wherein the excitation beam light source includes light from the second laser. [Item 12] The photodetector generates a particle detection signal due to scattering in the particle monitoring zone, the signal comprising: (i) the light from the incident beam; and (ii) the scattered light from the incident beam; and (iii) the scattered light by the excitation beam; and 12. The particle detection system according to any one of items 1 to 11, which corresponds to a total irradiance of 1000 nm. [Item 13] Item 13. The particle detection system of item 12, wherein the magnitude of the particle detection signal is at least twice as large as in the absence of the excitation beam. [Item 14] Item 14. A particle detection system according to any one of items 1 to 13, wherein the excitation beam intersects the particle monitoring zone at an oblique angle relative to the incident beam. [Item 15] 15. A particle detection system according to any one of items 1 to 14, wherein the excitation beam intersects the particle monitoring zone at a right angle to the incident beam. [Item 16] 16. A particle detection system according to any one of items 1 to 15, wherein the excitation beam intersects the particle monitoring zone in an opposite direction to the incident beam. [Item 17] 17. A particle detection system according to any one of items 1 to 16, wherein the excitation beam and the incident beam are guided in parallel through a positive lens that focuses the beams to a common focal point in the particle monitoring zone. [Item 18] 18. The particle detection system of any one of items 1 to 17, wherein the particle monitoring zone comprises a flow cell configured to flow particles. [Item 19] 19. The particle detection system of any one of items 1 to 18, wherein the excitation beam has an irradiance ratio of at least 1, the irradiance ratio being defined as the ratio of the irradiance at a waist of the excitation beam to the irradiance at a waist of the incident beam. [Item 20] 20. The particle detection system of claim 19, wherein the irradiance ratio of the excitation beams is at least 2. [Item 21] 20. The particle detection system of claim 19, wherein the excitation beam irradiance ratio is at least 10. [Item 22] 22. The particle detection system of any one of items 1 to 21, wherein the excitation beam light source comprises a single mode laser. [Item 23] 23. The particle detection system according to any one of items 1 to 22, wherein the particle monitoring zone is a flow cell. [Item 24] 24. The particle detection system of any one of items 1 to 23, wherein the particle monitoring zone is an aerosol jet. [Item 25] 25. The particle detection system of any one of items 1 to 24, wherein the particle monitoring zone is a surface. [Item 26] 26. The particle detection system according to any one of items 1 to 25, wherein the optical detector is a multi-element optical detector. [Item 27] 27. A particle detection system according to any one of items 1 to 26, comprising a diffractive optical element disposed in the path of the incident beam between the incident beam source and the particle monitoring zone. [Item 28] Item 28. The particle detection system of item 27, wherein the diffractive optical element is configured to generate a one-dimensional beam array. [Item 29] Item 28. The particle detection system of item 27, wherein the diffractive optical element is configured to generate a plurality of Gaussian beams. [Item 30] 28. The particle detection system of claim 27, wherein the diffractive optical element is configured to generate a plurality of beams, each of the plurality of beams having an intensity variance of less than 20% compared to the other beams. [Item 31] Item 28. The particle detection system of item 27, wherein the photodetector comprises an upper zone and a lower zone. [Item 32] 28. The particle detection system of claim 27, wherein the optical detector is a differential array detector. [Item 33] Item 33. The particle detection system according to any one of items 1 to 32, wherein the incident beam is a dark beam. [Item 34] Item 34. The particle detection system according to any one of items 1 to 33, wherein the excitation beam is a dark beam. [Item 35] 35. The particle detection system of any one of items 1 to 34, wherein the excitation beam is a dual-path beam. [Item 36] 36. The particle detection system according to any one of items 1 to 35, which is an excitation homodyne interferometric detection system. [Item 37] 37. The particle detection system according to any one of items 1 to 36, which is an excited self-homodyne interferometric detection system. [Item 38] 38. The particle detection system according to any one of items 1 to 37, which is an excitation heterodyne interferometric detection system. [Item 39] 39. An interceptor-type optical particle counter comprising the particle detection system according to any one of items 1 to 38. [Item 40] Item 40. The optical particle counter of item 39, wherein the optical detector is a first optical detector, and the optical particle counter comprises a second optical detector arranged to detect the excitation beam after passing through the particle monitoring zone. [Item 41] an incident beam light source that emits an incident beam; a particle monitoring zone disposed in the path of the incident beam; a photodetector disposed to detect the incident beam after passing through the particle monitoring zone; an excitation beam light source that emits an excitation beam directed toward the particle monitoring zone; Equipped with The photodetector light from the incident beam; and forward scattered light due to scattering of the incident beam in the particle monitoring zone; scattered light due to scattering of the excitation beam in the particle monitoring zone; the incident beam, the excitation beam, and the photodetector are arranged to detect a combination of A particle detection system wherein the excitation beam irradiance ratio is at least 1. [Item 42] Item 42. The particle detection system of item 41, wherein the irradiance ratio is defined as the ratio of the irradiance at the waist of the excitation beam to the irradiance at the waist of the incident beam. [Item 43] an incident beam light source for providing an incident beam; a particle monitoring zone disposed in the path of the incident beam and containing a fluid stream having particles; a diffractive optical element disposed in the path of the incident beam between the incident beam source and the particle monitoring zone; a photodetector disposed to detect the incident beam after passing through the particle monitoring zone; Equipped with 1. A particle detection system, comprising: an incident beam and a photodetector arranged such that the photodetector detects light from the incident beam and scattered light resulting from scattering of the incident beam from particles in the fluid stream in the particle monitoring zone. [Item 44] Item 44. The particle detection system of item 43, wherein the diffractive optical element is configured to generate a one-dimensional beam array. [Item 45] Item 45. A particle detection system according to item 43 or 44, wherein the diffractive optical element is configured to generate a plurality of Gaussian beams. [Item 46] 46. The particle detection system of any one of items 43 to 45, wherein the diffractive optical element is configured to generate a plurality of beams, each of the plurality of beams having an intensity variance of less than 5% compared to the other beams. [Item 47] Item 47. A particle detection system according to any one of items 43 to 46, wherein the photodetector comprises an upper zone and a lower zone. [Item 48] 48. The particle detection system according to any one of items 43 to 47, wherein the photodetector is a differential array detector. [Item 49] an incident beam light source for providing an incident beam; a particle monitoring zone disposed in the path of the incident beam and containing particles; a photodetector disposed to detect the incident beam after it leaves the particle monitoring zone; an excitation beam source providing an excitation beam directed into the particle monitoring zone; Equipped with The photodetector light from the incident beam; and scattered light resulting from scattering of the incident beam from the particles in the fluid stream in the particle monitoring zone; scattered light due to scattering of the excitation beam from the particles in the fluid stream in the particle monitoring zone; the incident beam, the excitation beam, and the photodetector are arranged to detect a combination of: [Item 50] 1. A method of particle detection comprising: directing the incident beam onto a monitoring zone containing the fluid stream having particles and onto a photodetector; directing an excitation beam into the particle monitoring zone; generating scattered light due to interaction of the incident beam with one or more particles in the particle monitoring zone; generating scattered light from the excitation beam interacting with one or more particles in the fluid stream in the particle monitoring zone; The photodetector light from the incident beam or reference beam; Scattered light from the incident beam; and scattered light from the excitation beam; detecting a combination of A method comprising: [Item 51] The photodetector light from the incident beam; and Scattered light from the incident beam; and scattered light from the excitation beam; Item 51. The method of item 50, comprising detecting a combination of: [Item 52] The photodetector light from the reference beam; and Scattered light from the incident beam; and scattered light from the excitation beam; Item 51. The method of item 50, comprising detecting a combination of: [Item 53] emitting a laser beam from a laser; splitting the laser beam into the excitation beam and the incident beam by a polarizing beam splitter; 53. The method according to any one of Items 50 to 52, comprising: [Item 54] generating the incident beam with a first laser; generating the excitation beam with a second laser; 53. The method according to any one of Items 50 to 52, comprising: [Item 55] 55. The method of any one of items 50 to 54, comprising generating a particle detection signal by the photodetector, the signal corresponding to the intensity of the light from the incident beam combined with the scattered light from the incident beam and the scattered light from the excitation beam. [Item 56] 56. The method of any one of items 50 to 55, wherein the incident beam and the excitation beam are configured to simultaneously interact with the particles in the fluid stream. [Item 57] 57. The method of any one of items 50 to 56, wherein the scattered light is generated by the interaction of the incident beam and the excitation beam with a single particle in the fluid stream. [Item 58] 58. The method of any one of items 50 to 57, comprising diffracting the incident beam into a plurality of beams by a diffractive optical element. [Item 59] 59. The method of claim 58, wherein the photodetector includes an upper zone and a lower zone, the method including the step of comparing a signal from the upper zone with a signal from the lower zone. [Item 60] 60. The method of any one of items 50 to 59, comprising increasing a volumetric sampling rate of the fluid flow by the diffracting step. [Item 61] 61. The method of any one of items 50 to 60, wherein the detecting step comprises detecting forward scattered light from the incident beam. [Item 62] Item 62. The method of any one of items 50 to 61, comprising the step of generating a high aspect ratio incident beam by directing the incident beam through a cylindrical lens. [Item 63] 1. A method of particle detection comprising: directing an incident beam onto a particle; directing an excitation beam at the particle; scattering light from the incident beam by the particles; scattering light from the excitation beam by the particles; By the photodetector, light from the incident beam; and Scattered light from the incident beam; and scattered light from the excitation beam; detecting a combination of A method comprising: [Item 64] 1. A method of particle detection comprising: generating an incident beam; diffracting the incident beam into a plurality of beams by a diffractive optical element; directing the plurality of beams onto a monitoring zone containing particles and a photodetector; generating scattered light from interactions of the plurality of beams with one or more particles in the particle monitoring zone; detecting scattered light from the plurality of beams with the photodetector; A method comprising: [Item 65] Item 65. The method of item 64, wherein the photodetector includes an upper zone and a lower zone, the method including the step of comparing a signal from the upper zone with a signal from the lower zone. [Item 66] 66. The method of claim 64 or 65, comprising increasing the volumetric sampling rate of the fluid flow by the diffraction step. [Item 67] Item 67. The method of any one of items 64 to 66, wherein the detecting step comprises detecting forward scattered light from the incident beam. [Item 68] 1. A method of particle detection comprising: directing the incident beam onto a monitoring zone containing the fluid stream having particles and onto a photodetector; directing an excitation beam into the particle monitoring zone; generating scattered light due to interaction of the incident beam with one or more particles in the fluid stream in the particle monitoring zone; generating scattered light from the excitation beam interacting with one or more particles in the fluid stream in the particle monitoring zone; The photodetector light from the incident beam; and Scattered light from the incident beam; and scattered light from the excitation beam; detecting a combination of A method comprising:

Claims

1. an incident beam light source for providing an incident beam; a particle monitoring zone disposed in the path of the incident beam and containing particles; a photodetector disposed to detect the incident beam after it leaves the particle monitoring zone; an excitation beam source providing an excitation beam directed into the particle monitoring zone; Equipped with The photodetector light from the incident beam; and scattered light resulting from scattering of the incident beam from the particles in the fluid stream in the particle monitoring zone; scattered light due to scattering of the excitation beam from the particles in the fluid stream in the particle monitoring zone; the incident beam, the excitation beam, and the photodetector are arranged to detect a combination of the scattered light resulting from scattering of the incident beam and the scattered light resulting from scattering of the excitation beam are coherent and parallel to the incident beam; A particle detection system wherein the scattered light from the excitation beam is coherent and parallel to the scattered light from the incident beam.

2. The particle detection system of claim 1 , wherein the incident beam intersects the excitation beam at the particle monitoring zone.

3. 3. A particle detection system according to claim 1, wherein the scattered light resulting from scattering of the incident beam in the particle monitoring zone is forward scattered light.

4. the incident beam is polarized before entering the particle monitoring zone; the excitation beam is polarized before entering the particle monitoring zone; 4. A particle detection system according to claim 1, wherein the incident beam and the excitation beam are configured such that the polarization axis of the incident beam is within 5° of the polarization axis of the excitation beam at the particle monitoring zone.

5. 5. The particle detection system of claim 1, wherein in the photodetector, the polarization axes of the scattered light due to scattering of the incident beam, the scattered light due to scattering of the excitation beam, and the light from the incident beam are within 5° of each other.

6. a laser and a polarizing beam splitter; the incident beam light source includes light from the laser guided on a first optical path through the polarizing beam splitter; 6. A particle detection system according to any one of claims 1 to 5, wherein the excitation beam light source comprises light from the laser guided on a second optical path through the polarizing beam splitter.

7. a first laser and a second laser; the incident beam light source includes light from the first laser; A particle detection system according to any preceding claim, wherein the excitation beam light source comprises light from the second laser.

8. The photodetector generates a particle detection signal due to scattering in the particle monitoring zone, the signal comprising: (i) the light from the incident beam; and (ii) the scattered light from the incident beam; and (iii) the scattered light by the excitation beam; and 8. A particle detection system according to claim 1, which is compatible with a total irradiance of 1000 nm.

9. 9. The particle detection system of claim 8, wherein the particle detection signal is at least twice as large in magnitude as it is without the excitation beam.

10. A particle detection system according to any preceding claim, wherein the excitation beam intersects the particle monitoring zone at an oblique angle relative to the incident beam.

11. A particle detection system according to any preceding claim, wherein the excitation beam intersects the particle monitoring zone at a right angle to the incident beam.

12. A particle detection system according to any preceding claim, wherein the excitation beam intersects the particle monitoring zone in an opposite direction to the incident beam.

13. A particle detection system according to any preceding claim, wherein the excitation beam and the incident beam are guided in parallel through a positive lens that focuses the beams to a common focal point in the particle monitoring zone.

14. A particle detection system according to any preceding claim, wherein the particle monitoring zone comprises a flow cell configured to flow particles.

15. 15. A particle detection system according to any one of claims 1 to 14, wherein the excitation beam has an irradiance ratio of at least 1, the irradiance ratio being defined as the ratio of irradiance at a waist of the excitation beam to the irradiance at a waist of the incident beam.

16. 16. The particle detection system of claim 15, wherein the excitation beam irradiance ratio is at least 2.

17. 16. The particle detection system of claim 15, wherein the excitation beam irradiance ratio is at least 10.

18. A particle detection system according to any preceding claim, wherein the excitation beam light source comprises a single mode laser.

19. A particle detection system according to any preceding claim, wherein the particle monitoring zone is a flow cell.

20. A particle detection system according to any preceding claim, wherein the particle monitoring zone is an aerosol jet.

21. A particle detection system according to any preceding claim, wherein the particle monitoring zone is a surface.

22. A particle detection system according to any one of claims 1 to 21, wherein the optical detector is a multi-element optical detector.

23. A particle detection system according to any preceding claim, comprising a diffractive optical element disposed in the path of the incident beam between the incident beam source and the particle monitoring zone.

24. 24. The particle detection system of claim 23, wherein the diffractive optical element is configured to generate a one-dimensional beam array.

25. 24. The particle detection system of claim 23, wherein the diffractive optical element is configured to generate a plurality of Gaussian beams.

26. 24. The particle detection system of claim 23, wherein the diffractive optical element is configured to generate a plurality of beams, each of the plurality of beams having an intensity variance of less than 20% compared to the other beams.

27. 24. The particle detection system of claim 23, wherein the photodetector includes an upper zone and a lower zone.

28. 24. The particle detection system of claim 23, wherein the optical detector is a differential array detector.

29. A particle detection system according to any preceding claim, wherein the incident beam is a dark beam.

30. A particle detection system according to any one of claims 1 to 29, wherein the excitation beam is a dark beam.

31. A particle detection system according to any one of claims 1 to 30, wherein the excitation beam is a dual-path beam.

32. A particle detection system according to any one of claims 1 to 31, which is an excitation homodyne interferometric detection system.

33. A particle detection system according to any one of claims 1 to 32, which is an excited self-homodyne interferometric detection system.

34. A particle detection system according to any one of claims 1 to 33, which is an excitation heterodyne interferometric detection system.

35. An interruption-type optical particle counter comprising a particle detection system according to any one of claims 1 to 34.

36. 36. The optical particle counter of claim 35, wherein the optical detector is a first optical detector, and the optical particle counter comprises a second optical detector positioned to detect the excitation beam after passing through the particle monitoring zone.

37. 1. A method of particle detection, said method comprising: directing the incident beam onto a monitoring zone containing the fluid stream having particles and onto a photodetector; directing an excitation beam into the particle monitoring zone; generating scattered light from the incident beam interacting with one or more particles in the particle monitoring zone; generating scattered light from the excitation beam interacting with one or more particles in the fluid stream in the particle monitoring zone; The photodetector light from the incident beam; and Scattered light from the incident beam; and scattered light from the excitation beam; detecting a combination of Including, the scattered light resulting from scattering of the incident beam and the scattered light resulting from scattering of the excitation beam are coherent and parallel to the incident beam; A method wherein the scattered light from the excitation beam is coherent and parallel to the scattered light from the incident beam.

38. emitting a laser beam from a laser; splitting the laser beam into the excitation beam and the incident beam by a polarizing beam splitter; 38. The method of claim 37, comprising:

39. generating the incident beam with a first laser; generating the excitation beam with a second laser; 38. The method of claim 37, comprising:

40. 40. The method of any one of claims 37 to 39, comprising generating a particle detection signal by the photodetector, the signal corresponding to the intensity of the light from the incident beam combined with the scattered light from the incident beam and the scattered light from the excitation beam.

41. A method according to any one of claims 37 to 40, wherein the incident beam and the excitation beam are configured to simultaneously interact with the particles in the fluid stream.

42. A method according to any one of claims 37 to 41, wherein the scattered light is produced by the interaction of the incident beam and the excitation beam with a single particle in the fluid stream.

43. A method according to any one of claims 37 to 42, comprising diffracting the incident beam into a plurality of beams by a diffractive optical element.

44. 44. The method of claim 43, wherein the photodetector includes an upper zone and a lower zone, the method including comparing a signal from the upper zone with a signal from the lower zone.

45. A method according to any one of claims 37 to 44, comprising increasing the volumetric sampling rate of the fluid flow by said diffracting step.

46. A method according to any one of claims 37 to 45, wherein the detecting step comprises detecting forward scattered light from the incident beam.

47. A method according to any one of claims 37 to 46, comprising the step of generating a high aspect ratio incident beam by directing the incident beam through a cylindrical lens.

48. 1. A method of particle detection, said method comprising: directing an incident beam onto a particle; directing an excitation beam at the particle; scattering light from the incident beam by the particles; scattering light from the excitation beam by the particles; By the photodetector, light from the incident beam; and Scattered light from the incident beam; and scattered light from the excitation beam; detecting a combination of It contains the scattered light resulting from scattering of the incident beam and the scattered light resulting from scattering of the excitation beam are coherent and parallel to the incident beam; A method wherein the scattered light from the excitation beam is coherent and parallel to the scattered light from the incident beam.

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