Apparatus and method for characterizing particles

Abstract

The invention relates to a device (1) for characterizing particles, comprising a light source (2) for projecting a light beam (4) along a beam axis (5); comprising a beam shaping optical unit (3) which is arranged along a beam axis (5) and is designed to adjust a position-dependent intensity distribution of a light beam (4) in a measurement volume (6) extending in sections along the beam axis (5). The detector (10) is designed to detect the measurement beam (8) reflected and / or scattered by the particles (7) when the particles (7) are located in the measurement volume (6) and to output an intensity signal to the evaluation unit. The evaluation unit is configured to determine a particle property within the measurement volume as a function of the intensity signal. The beam shaping optical unit (3) is configured to shape the intensity distribution on a projection plane (x-y) extending transversely to the beam axis (5) such that the intensity of the light beam is minimum along the outer contour (15) of the ellipse (11) and maximum at at least one point (14) within the ellipse (11).

Description

Background Art

[0001] The invention relates to a device according to the preamble of claim 1 and to a method according to the preamble of claim 12 .

[0002] Apparatus and methods of the type mentioned at the outset are known per se and are used in various applications to determine particle properties, such as particle position, particle velocity or, for example, particle size. For example, this information can be used to monitor or control industrial manufacturing and processing processes.

[0003] For example, a device for determining particle properties is known from DE 10 2019 209 213 A1, and the device comprises a light source, by means of which a light beam is projected along a beam axis. A beam shaping optical unit is arranged along the beam axis. The beam shaping optical unit is designed to adjust the position-dependent intensity distribution of the light beam in a measurement volume extending along the beam axis in sections. The particles to be characterized located in the measurement volume reflect or scatter the light beam at least partially as a measurement beam. The measurement beam is detected by a detector, which outputs an intensity signal to an analysis unit. The analysis unit is used to determine the particle properties in the measurement volume based on the intensity signal.

[0004] Purpose of the Invention

[0005] In principle, it is desirable to be able to characterize particles within a measurement volume with high accuracy. It is possible to improve the accuracy compared to previously known devices, for example by increasing the power of the light source used, but this is usually associated with high costs. It is therefore an object of the present invention to propose a device and a method associated with a good ratio between the achievable accuracy of characterizing particles and the costs incurred thereby. Summary of the invention

[0006] This object is achieved by a device having the features according to claim 1 and by a method having the features according to claim 12. Advantageous developments are the subject matter of the respective dependent claims.

[0007] In a manner known per se, the device according to the invention has a light source for projecting at least one light beam along a beam axis. A beam shaping optical unit is arranged along the beam axis and is designed to adjust the position-dependent intensity distribution of the light beam in a measurement volume extending in sections along the beam axis. The detector is used to detect the measurement beam reflected and / or scattered by particles in the measurement volume and to output at least one intensity signal to an evaluation unit. The evaluation unit is designed to determine the particle properties in the measurement volume based on the intensity signal.

[0008] The device according to the invention differs from previously known devices in that the beam shaping optical unit is designed so that the position-dependent intensity distribution in a projection plane extending transversely to the beam axis within the measurement volume is configured in such a way that the intensity of the light beam is minimum along the outer contour of the ellipse and maximum at at least one point within the ellipse.

[0009] The invention is based on the discovery that the adjustment of a position-dependent intensity distribution in which the light beam has a substantially elliptical shape in the projection plane is associated with an increase in the accuracy with which the properties of the particles are determined over a larger spatial region. Compared to a radially symmetrical intensity distribution in which the intensity of the light beam is, for example, minimum along a circular contour, the intensity distribution extends over a larger length along the vertical axis of the ellipse and over a smaller length along the transverse axis of the ellipse. In addition, the light beam can be more easily focused along the vertical axis than along the transverse axis. Compared to previously known devices, the light beam can therefore have an overall higher power per unit area for the same light source power in the projection plane. This means that the light beam can be reflected and / or scattered by the particles in the measurement volume with a correspondingly higher intensity. The particles can be characterized with a high spatial resolution over a larger spatial region, in particular along the vertical axis of the ellipse.

[0010] Advantageously, the intensity of the light beam is at a maximum at least at the surface center point of the ellipse, wherein in particular a Gaussian intensity distribution can be present. The intensity decreases continuously from the surface center point toward the outer contour of the ellipse. In particular, the ellipse has a vertical axis and a horizontal axis, in connection with which the ellipse is configured symmetrically with respect to the vertical axis and the horizontal axis, respectively, and the dimension along the vertical axis is greater than the dimension along the horizontal axis. Preferably, the ellipse is an ellipse and in particular not a circle.

[0011] The particle property can be, for example, the size of the particle or preferably the position of the particle along the vertical axis of the ellipse in the projection plane. In particular, the device is designed such that the position of the particle along the vertical axis can be determined with a spatial resolution of 1 micrometer. Preferably, the detector has a spatial resolution of from 5 micrometers to 0.1 micrometers, particularly preferably from 3 micrometers to 1 micrometer, most preferably 1 micrometer in the measurement volume.

[0012] The particle can be a solid in a gas, vacuum or liquid. It can also be an oil drop in a water bath, or vice versa, a water drop in an oil bath. It can also be a liquid drop in a gas or vacuum, or in particular, a liquid drop emitted from a nozzle, in particular a spray nozzle.

[0013] The invention is not limited to a specific embodiment of the light source. In a simple embodiment, the light source comprises at least one laser having a laser diode, a superluminescent diode, a halogen emitter or a similar beam source.

[0014] Within the scope of the present invention, at least the light source and the detector may be present in a transmission arrangement or a reflection arrangement. In a transmission arrangement, the light source and the detector are arranged on different sides of the projection plane. Here, the light beam is scattered by the particles to be characterized, so that the measurement beam exists as a transmission beam. In a reflection arrangement, the light source and the detector are arranged on the same side relative to the projection plane. The light beam is reflected by the particles to be characterized, so that the measurement beam exists as a reflection beam. The scope of the present invention also lies in providing at least two detectors, wherein the first detector and the light source are arranged on different sides of the projection plane, and wherein the second detector and the light source are arranged on one side of the projection plane. In such an embodiment, a combination of a reflection arrangement and a transmission arrangement between the light source and the detector is provided.

[0015] The beam shaping optical unit may comprise a cylindrical lens, wherein the lens surface is curved on one axis, and by means of which the intensity distribution of the light beam according to the invention can be adjusted. The detector may comprise a condenser lens, by means of which the measuring beam is focused and directed onto at least one sensor element of the detector. In particular, the sensor element is a photodiode which, upon detection of the measuring beam, emits an electrical signal to an evaluation unit and the amplitude of which preferably depends on the intensity of the measuring beam.

[0016] Preferably, at least the light source and the beam shaping optical unit are arranged stationarily along the beam axis and in particular in defined alignment with each other. At least in the reflection arrangement, the detector is preferably arranged with a measuring axis at an angle to the beam axis of the light beam, along which the measuring beam can be detected.

[0017] The evaluation unit can be designed as an electronic computing unit, with the aid of which the particle properties can be determined. A mathematical model can be implemented on the evaluation unit, which describes the relationship between the intensity of the measuring beam and the particle properties determined analytically or empirically. By measuring the intensity of the measuring beam, the intensity signal output by the detector can be assigned to the particle property to be determined using the mathematical model.

[0018] Additionally or alternatively, discrete table values ​​can be stored on the evaluation unit, with the aid of which measured intensity values ​​of the measuring beam can be compared with stored intensity values ​​and assigned to associated particle properties.

[0019] Additionally or alternatively, at least one characteristic curve can be stored in the evaluation unit, which indicates the intensity profile as a function of the degree of the particle characteristic. Using the characteristic curve, the measured intensity of the measurement beam can be assigned to the particle characteristic to be determined. In particular, the characteristic curve describes the profile of the intensity of the measurement beam as a function of the particle position along an axis in the projection plane, in particular the vertical axis of an ellipse.

[0020] In an advantageous embodiment, the beam shaping optical unit is designed to adjust a position-dependent polarization distribution in the projection plane in addition to the position-dependent intensity distribution, wherein a first polarization and a second polarization having different polarization directions are present along the vertical axis of the ellipse. The detector is designed to determine at least two intensities of the measuring beam having the first polarization and / or the second polarization and to output two polarization-dependent intensity signals to the evaluation unit. The evaluation unit is designed to determine the particle property based on the two polarization-dependent intensity signals.

[0021] The above-described expansion is based on the applicant's finding that the intensity of the measuring beam may depend on a plurality of particle properties simultaneously, such as the particle position and the particle size. This makes it difficult to determine only one of these particle properties uniquely and unambiguously, since, for example, varying particle sizes between different particles to be characterized with the same particle position may lead to different measurable intensities. Due to the design of the beam shaping optical unit, the position-dependent intensity distribution and the position-dependent polarization distribution in the projection plane can be adjusted by means of the beam shaping optical unit, and further light properties of the light beam can be adjusted and taken into account. This makes it possible to take into account not only the intensity of the measuring beam, but also the polarization, so as to be able to determine a unique and unambiguous particle property, in particular the particle position. Such an embodiment of the intensity distribution and the polarization distribution means that the measuring beam reflected and / or scattered by the particles can have at least two intensity components with different polarizations.

[0022] For a better understanding, consider the following example of position determination for three particles: If a first particle is located in the measurement volume and scatters or reflects a light beam with a first intensity and a first polarization, the first intensity and the first polarization can be assigned to the first particle position. If a second particle is located in the measurement volume and scatters or reflects a light beam with a second polarization and a second intensity that is higher than the first intensity, it can be concluded that the second particle is at a second position. If a third particle is located in the measurement volume and scatters or reflects a light beam with a second intensity and the first polarization, it can be concluded that the third position of the third particle corresponds to the first position of the first particle and that the second intensity is due to the larger particle size.

[0023] In a simple embodiment, the beam shaping optical unit may comprise a so-called delay plate, which generates a desired position-dependent polarization distribution with a first polarization direction and a second polarization direction. Such a delay plate is an optical component which can change the polarization and phase of a passing light wave as required. Preferably, the delay plate is configured as a so-called spatial polarization converter, which is known, for example, from EP 2705393 B1 and can be manufactured according to the method known from US20200408953 A1. Alternatively, a so-called spatial light modulator or a so-called vortex plate can also be used to generate the position-dependent polarization distribution.

[0024] For example, the detector may include two photodiodes, each of which has a polarization filter to enable polarization-sensitive triggering. The first photodiode may be configured such that it outputs a first electrical signal based on the intensity of a measurement beam having a first polarization. The second photodiode may be designed such that it outputs a second electrical signal based on the intensity of a measurement beam having a second polarization.

[0025] In a simple embodiment, a mathematical model can be implemented in the evaluation unit in the manner already described, which mathematical model assigns a plurality of intensity values ​​with different polarizations to a corresponding number of particle properties, in particular particle positions. In particular, the evaluation unit can have a stored evaluation routine, by means of which at least two intensity values ​​with different polarizations are set relative to one another and the ratio is assigned to the particle positions using a mathematical model and / or a table and / or a characteristic curve. Instead of the above-mentioned ratio, a characteristic value (Kennzahl) corresponding to the ratio can also be determined.

[0026] In an advantageous embodiment, the beam shaping optical unit is designed to generate a position-dependent polarization distribution such that an angle of 180 degrees exists between the polarization direction of the first polarization and the polarization direction of the second polarization. At least one third polarization is present along the vertical axis of the ellipse, preferably in the region of the point of maximum intensity within the ellipse. An angle of 90 degrees exists between the polarization direction of the first polarization and the polarization direction of the third polarization and / or between the polarization direction of the second polarization and the polarization direction of the third polarization.

[0027] The above-mentioned expansion scheme makes it possible to further improve the accuracy in determining the particle characteristics. In this regard, the beam shaping optical unit is configured to adjust the third polarization. In addition, the detector is configured to detect the intensity of the measurement beam with the third polarization. The analysis unit is further designed to determine the particle characteristics based on the three intensity signals under the first polarization, the second polarization and the third polarization.

[0028] In another advantageous extension, the beam shaping optical unit is designed to produce a position-dependent polarization distribution so that a fourth polarization is present along the vertical axis of the ellipse and between the first polarization and the third polarization and / or between the second polarization and the third polarization, wherein an angle of 45 degrees is present between the polarization direction of the fourth polarization and the polarization direction of the third polarization.

[0029] The above-mentioned expansion scheme makes it possible to further improve the accuracy in determining the particle characteristics. In this regard, the beam shaping optical unit is configured to adjust the fourth polarization. In addition, the detector is configured to detect the intensity of the measurement beam with the fourth polarization. The analysis unit is further designed to determine the particle characteristics based on the four intensity signals under the first polarization, the second polarization and the third polarization and the fourth polarization.

[0030] In an advantageous embodiment, the detector is designed such that polarization-dependent intensity components of the measuring beam can be determined in at least two of the following polarizations: 0 degrees, 45 degrees, 90 degrees, 135 degrees.

[0031] The above-mentioned embodiment is advantageous because the mentioned polarization direction can be easily adjusted using common beam shaping optical units. The detector can have a plurality of photodiodes, which have at least two polarization filters, which are arranged relative to each other so that light from the photodiodes is detected only in the polarization direction of the polarization filter.

[0032] Preferably, there is no phase difference or a phase difference of 180° between the parts of the light beam with different polarization directions. This makes it easy to adjust the linear polarization. However, the applicant's research has also shown that in order to be able to uniquely and clearly determine the particle properties, in particular the particle position, it is also advantageous to adjust the circular polarization or the elliptical polarization. In an advantageous extension, the light source and / or the beam shaping optical unit is therefore configured to generate at least two light beams with a phase difference, wherein the phase difference is 90 degrees in order to at least partially adjust the circular polarization in the projection plane, or wherein the phase difference is between 0 and 90 degrees or between 90 and 180 degrees in order to at least partially adjust the elliptical polarization in the projection plane.

[0033] In a further advantageous embodiment, the light source and / or the beam shaping optical unit is designed to shape the position-dependent intensity distribution in the projection plane in such a way that the intensity of the light beam along the two outer contours of the two ellipses is minimal and the intensity distribution is maximal in the region of the vertical axes of the two ellipses, which are arranged in a V-shape relative to one another. The detector is designed to detect the intensities of the two measurement beams in a time-shifted manner. The evaluation unit is used to determine the particle position within the measurement volume based on the time interval between the measured intensities of the two measurement beams.

[0034] The above-described extension is based on the following discovery of the applicant: In order to be able to reliably determine the particle properties, in particular the particle position, the embodiment of the position-dependent intensity distribution of the light beam, in which the intensity is minimum along the outer contour of the ellipse, can be doubled in the projection plane. When the particle passes through the projection plane in the measurement volume and through the vertical axes of the two ellipses, the two measuring beams are reflected and / or scattered in a mutually time-shifted manner and detected by the detector with a corresponding time shift. If the angle between the vertical axes arranged in a V-shape relative to each other is known and the particle velocity is known, the particle position can be determined by taking into account the time interval between the two intensity signals. This extension is particularly advantageous if the particle velocities of the multiple particles to be characterized do not differ and are known.

[0035] Alternatively, the device can be configured so that the intensity of the beams along the three outer contours of the three ellipses is minimal and the intensity distribution is maximal in the region of the vertical axes of the three ellipses, which are arranged in an N-shape relative to each other. The detector is configured to detect the intensity of the three measurement beams in a time-shifted manner. The analysis unit is used to determine the particle position within the measurement volume based on at least two time intervals between the measured intensities of the three measurement beams.

[0036] One advantage of the above-described development is that the particle position within the measurement volume can be determined independently of the particle velocity. In particular, the particle position can be determined based on the ratio of two time intervals. The applicant has found that determining such a ratio of two time intervals allows the particle position to be reliably determined even when the particle velocity varies and is unknown.

[0037] In a further advantageous embodiment, the light source and / or the beam shaping optical unit is designed to project two light beams with different wavelengths respectively along the beam axis, the two light beams overlapping in the projection plane and thus having a position-dependent intensity distribution and a position-dependent wavelength distribution. The detector is designed to detect at least one wavelength-dependent intensity of the measuring beam. The evaluation unit is designed to determine the particle position within the measurement volume based on the wavelength-dependent intensity of the measuring beam.

[0038] With the position-dependent wavelength distribution, in addition to the intensity of the measuring beam, other light properties can also be taken into account in order to be able to uniquely and unambiguously determine the particle characteristics. In particular, in addition to or as an alternative to the position-dependent polarization distribution, a position-dependent wavelength distribution can be used in order to be able to uniquely and unambiguously determine the position of the particle within the measurement volume. The position-dependent intensity distribution can be configured to be symmetrical with respect to the vertical axis and the horizontal axis of the ellipse. For example, the position-dependent wavelength distribution can be different at two spaced-apart positions along the vertical axis. This embodiment of the intensity distribution and the wavelength distribution means that the light beam reflected by the particle in the form of the measuring beam can have at least two wavelength components, consideration of which makes it possible to uniquely and unambiguously determine the position of the particle within the projection plane.

[0039] The detector can have a plurality of photodiodes which are configured to be wavelength-sensitive so that detected measuring beams with different wavelength components result in different signal amplitudes for the corresponding photodiodes. The wavelength-dependent signal can be evaluated using mathematical models, tables or characteristic curves to determine particle properties, in particular particle positions.

[0040] In an advantageous embodiment, the measurement volume has a length along the beam axis which corresponds to twice the Rayleigh length of the beam.

[0041] The Rayleigh length describes in a manner known per se the distance along the beam axis between the focal plane and the position where its cross-sectional area doubles relative to the focal plane. Thus, the size and / or position of the measurement volume relative to the beam axis can be adjusted based on the properties of the beam, in particular its focal plane.

[0042] Preferably, the beam shaping optical unit and / or the detector are designed to form a measurement volume depending on the application and with adjustable size. Preferably, the ellipse in the projection plane has a height between 10 micrometers and 1000 micrometers and / or a width between 100 micrometers and 5 centimeters.

[0043] In particular, one advantage of determining the particle position based on a plurality of polarization-dependent intensity values ​​is that no camera system is required. Instead, the particle position can be determined based on discrete values, wherein both the detector and the evaluation unit can have a simple design. Studies by the applicant have shown that the evaluation unit can be configured to determine a plurality of particle positions at frequencies above 10 MHz.

[0044] In an advantageous embodiment, the light source and / or the beam shaping optical unit and / or the detector are arranged in a spatially fixed manner relative to one another in order to form a measurement volume in a fixed manner and to detect moving particles in the measurement volume. Alternatively, the light source and / or the beam shaping optical unit and / or the detector are arranged in a movable manner in order to displace the measurement volume by means of a scanning movement and to detect stationary particles in the measurement volume. Preferably, the light source and / or the beam shaping optical unit and / or the detector are arranged in a non-movable manner relative to one another during the scanning movement.

[0045] The scanning movement can be realized by means of locomotion known per se, such as an articulated arm robot or similar.In this embodiment of the device, a surface can in particular be inspected to determine whether it is contaminated by one or more particles.

[0046] As mentioned above, the object is also achieved by a method according to claim 12 .

[0047] In the method according to the invention for characterizing particles, a light beam is projected along a beam axis, wherein the light beam has a position-dependent intensity distribution in a measurement volume extending in sections along the beam axis. The particle to be characterized reflects or scatters the light beam in the measurement volume at least partially as a measurement beam. A property of the particle in the measurement volume is determined based on at least one intensity of the measurement beam.

[0048] It is essential for the method that the position-dependent intensity distribution in a projection plane extending transversely to the beam axis in the measurement volume is minimum along the outer contour of the ellipse and maximum at at least one point within the ellipse, in particular at the surface center of the ellipse.

[0049] Preferably, the method can be performed by means of the device according to the invention or its advantageous developments. Therefore, the same remarks already provided above with regard to the device according to the invention and the advantageous developments apply to the advantages that can be achieved here.

[0050] In an advantageous embodiment, a light beam is generated with a spatially dependent polarization distribution and the particle properties are ascertained as a function of the polarization-dependent intensity of the measurement beam.

[0051] In a further advantageous embodiment, light beams with different wavelengths are generated which overlap in the measurement volume, wherein the overlapping light beams have a position-dependent intensity distribution and a position-dependent wavelength distribution in the projection plane, and wherein the particles to be characterized in the measurement volume are determined based on the wavelength-dependent intensity of the measuring beams.

[0052] In another advantageous embodiment, a position-dependent intensity distribution is generated in the projection plane, so that the intensity of the light beam is minimum along the outer contour of the two ellipses and maximum in the region of the vertical axes of the two ellipses, which are arranged in a V-shape. The particle to be characterized reflects or scatters the light beam in the measurement volume at least partially into two measurement beams. The intensities of the two measurement beams are detected in a time-shifted manner. The particle properties, in particular the particle position, in the measurement volume are determined from the two time intervals between the measured intensities of the measurement beams.

[0053] Alternatively, a position-dependent intensity distribution is generated in the projection plane, so that the intensity of the beam is minimum along the outer contour of three ellipses and maximum in the region of the vertical axes of the three ellipses, which are arranged in the shape of an N. The intensities of the three measuring beams are detected in a time-shifted manner. The particle properties in the measurement volume are determined from two time intervals between the measured intensities of the measuring beams and preferably independently of the particle velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Further advantages of the invention are explained below with reference to exemplary embodiments and the accompanying drawings.

[0055] In the attached picture:

[0056] Figure 1 shows a schematic representation of an apparatus for characterizing particles according to the invention;

[0057] Figure 2 A first exemplary embodiment of a position-dependent intensity distribution and a position-dependent polarization distribution is shown;

[0058] Figure 3 shows a diagram with a plurality of polarization-dependent intensity profiles for determining the position of a particle;

[0059] Figure 4 A second exemplary embodiment of a position-dependent intensity distribution is shown;

[0060] Figure 5 A third exemplary embodiment of a position-dependent intensity distribution is shown;

[0061] Figure 6 A fourth exemplary embodiment of a spatially dependent intensity distribution is shown. DETAILED DESCRIPTION

[0062] Figure 1 A device 1 is shown, by means of which the particle position can be determined optically. For this purpose, the device 1 has a laser 2 and a beam-shaping optical unit 3, which comprises a swirl plate and a cylindrical lens in a manner not shown here.

[0063] The laser 2 is used to generate a light beam 4, which extends along a beam axis 5. In this case, a section of the light beam 4 along the beam axis 5 serves as a measurement volume 6, through which a moving particle 7 passes. Figure 1 , showing that the particle 7 is in two positions during the linear movement.

[0064] like Figure 2 and Figure 3 As shown in detail, the beam-shaping optical unit 3 with a cylindrical lens and a vortex plate serves to adjust the position-dependent intensity distribution and the position-dependent polarization distribution of the light beam 4 in a projection plane extending perpendicularly to the beam axis 5 .

[0065] Particles 7 located in measurement volume 6 reflect light beam 4 at least partially in the form of measurement beam 8 which is collected by a collecting lens 9 and guided to detector 10 . Measurement beam 8 has a plurality of polarization-dependent intensities which can be ascertained by detector 10 .

[0066] In the exemplary embodiment shown here, an evaluation unit integrated into detector 10 is used to determine the expected particle position within measurement volume 6 on the basis of at least one polarization-dependent intensity of measurement beam 8 .

[0067] As based on Figure 2 As shown, the light beam in the projection plane has essentially the shape of an ellipse 11 with two axes of symmetry, i.e., an ellipse. Along the vertical axis H, which extends vertically, the ellipse has a height dimension 12, which is greater than the width dimension 13 along the horizontal axis. The intensity of the light beam is distributed in such a way that the intensity is maximum at the face center point 14 of the ellipse 11 and minimum along the outer contour 15. Within the ellipse 11, there is a two-dimensional Gaussian intensity distribution in a plane perpendicular to the projection plane. In other words, the intensity extends continuously in the region between the face center point 14 and the circumferential outer contour 15, wherein the intensity decreases from the face center point 14 in the radial direction toward the outer contour 15.

[0068] Such an intensity distribution means that the light beam can be reflected with different intensities along the vertical axis H of the ellipse. By measuring the intensity of the measurement beam, the particle properties can be determined with high accuracy. If the particle property to be determined is the particle position, it is advantageous to take into account that the intensity of the measurement signal may also vary depending on the particle size. Therefore, Figure 2 The embodiment of the intensity distribution shown provides a beam shaping optical unit for generating a position-dependent polarization distribution in Figure 2Indicated by arrows 16, 17, 18, 19 and 20. Here, along the vertical axis H, there is a first polarization 16 and a second polarization 17, which are spaced apart from each other along the vertical axis H of the ellipse 11 and whose polarization directions are at an angle of 180 degrees to each other. In the region of the face center point 14, there is a third polarization 18, whose polarization direction is at a polarization angle of 90 degrees to the polarization directions of the first polarization and the second polarization. Between the first polarization 16 and the third polarization 18, there is a fourth polarization 19, whose polarization direction is at an angle of 45 degrees to the polarization direction of the third polarization 18. Between the second polarization 17 and the third polarization 18, there is a fifth polarization 20, which also has an angle difference of 45 degrees compared to the third polarization 18. In contrast to the schematic diagram shown, the position-dependent polarization distribution is continuous along the vertical axis H and includes discretely shown polarizations 16, 17, 18, 19 and 20.

[0069] If the particle 7 is located in the projection plane and in the region of the vertical axis H of the ellipse 11, the light beam is reflected so that the measuring beam has a plurality of intensity components with different polarizations. Taking these polarization-dependent intensity components into account, a unique and unambiguous position of the particle in the projection plane can be determined.

[0070] Figure 3 Graphs with position-dependent intensity profiles 21, 22, 23 and 24 are shown. These intensity profiles each depict the polarization-dependent intensity of the light beam along the vertical axis of the ellipse in its projection plane. Here, the first intensity profile 21 corresponds to a profile with a position-dependent intensity profile according to Figure 2 The second intensity course 22 corresponds to the position-dependent intensity of the light beam of the first polarization 18. Figure 2 The polarization direction of polarization 16 is at an angle of 180 degrees to the polarization direction of polarization 17, so that the polarization filter can transmit light with both polarizations 16 and 17. The third intensity variation process 23 corresponds to the position-dependent intensity of the light beam with the second polarization 16 and the third polarization 17 according to Figure 2 The fourth intensity variation process 24 corresponds to the position-dependent intensity of the light beam with the fourth polarization 19. Figure 2 The position-dependent intensity of the fifth polarized light beam 20.

[0071] If the particle is located in the projection plane of the beam - corresponding to Figure 2 In the image plane of , the reflected measurement beam has a plurality of polarization-dependent intensities which correspond to the polarizations according to Figure 3intensity profiles 21, 22, 23 and 24. For example, if the particle is located at a height of 0 μm along the y-axis, the measurement beam has a main intensity component corresponding to the first intensity profile 21 and has a corresponding first polarization 18. At the same time, the measurement beam in this example has less pronounced intensity components corresponding to the intensity profiles 23 and 24 and having a corresponding fourth polarization 19 and fifth polarization 20. In other words, at a y-position of 0 μm, according to Figure 2 The polarization 18 is dominant, but this can be achieved by Figure 2 It is represented by the linear superposition of equal parts of polarizations 19 and 20.

[0072] By measuring the polarization-dependent intensities using detector 10, these can be assigned to a unique and unambiguous position of the particle along the y-axis, for example using a mathematical model or table. Here, the asymmetric course of the intensity course 23, 24 in particular enables a unique and unambiguous distinction between the two particle positions along the y-axis.

[0073] exist Figure 1 In the exemplary embodiment of the device 1 shown, the light is split into two beams by a so-called 50:50 beam splitter, regardless of polarization. Two photodiodes are arranged along the optical path after the beam splitter, which are configured to detect different polarization components. In this regard, the first photodiode is configured to detect the polarization components according to Figure 2 The second photodiode is designed to detect polarizations 18, 16 and 17 of the measuring beam. When the separated measuring beam is detected, the photodiodes each output an electrical signal corresponding to the intensity of the corresponding measured light component of one of the mentioned polarizations. These signals are evaluated in the evaluation unit, for example using the mathematical model mentioned above.

[0074] Figure 4 shows an alternative embodiment of the intensity distribution in the projection plane, which can be obtained by Figure 1 The device 1 basically corresponds to the device forming the intensity distribution. Figure 1 Unlike the embodiment shown, the light source is designed to shape the position-dependent intensity distribution in the projection plane so that the intensity along the outer contour of the two ellipses 11, 11' (the vertical axes H, H' of the two ellipses are arranged in a V shape) is minimal and the intensity in the region of the vertical axes H, H' (in this case the surface center points 14, 14' of the two ellipses 11 or 11') is maximal. The detector is designed to detect the intensity of the two measurement beams in a time-shifted manner. The evaluation unit is designed to determine the particle position in the measurement volume based on the time interval between the measured intensities of the two measurement beams.

[0075] Figure 4The intensity distribution shown extends over a range of about 1 mm along the x-axis. In an alternative embodiment, the extension along the x-axis can be up to 3 mm. When a particle moving through the measurement volume parallel to the x-axis passes through the projection plane xy and through the vertical axes H, H' of two adjacent ellipses 11, 11', the two measurement beams are reflected in a mutually time-shifted manner and detected by the detector with a corresponding time shift. When the angle between the V-shaped vertical axes H, H' is known and the particle velocity is known, the particle position can be determined by considering the measured intensity. It is particularly advantageous to apply this extended scheme if the particle velocities of multiple particles to be characterized are known and there is no difference in the particle velocities. In this regard, the particle position can be directly inferred based on the measured time interval.

[0076] Figure 5 shows an alternative embodiment of the intensity distribution in the projection plane, which can be obtained by Figure 1 The device 1 basically corresponds to the device forming the intensity distribution. Figure 1 Unlike the device shown, the light source is designed to shape the position-dependent intensity distribution in the projection plane in such a way that the intensity along the outer contour of the three ellipses 11, 11', 11" (the vertical axes H, H', H" of the three ellipses are arranged in an N shape) is minimal and the intensity in the region of the vertical axes H, H', H" (in this case, the surface center points 14, 14' and 14" of the three ellipses 11, 11' and 11" respectively) is maximized, wherein the detector is designed to detect the intensities of the three measuring beams in a time-shifted manner, and wherein the analysis and processing unit is designed to determine the particle position within the measurement volume based on two time intervals between two measured intensities of the measuring beams and in particular independently of the particle velocity. Figure 5 The intensity distribution shown extends over a range of about 1 mm along the x-axis. In alternative embodiments, the extension along the x-axis may be up to 3 mm.

[0077] Figure 5 One advantage of the intensity distribution shown is that the particle position within the measurement volume can be determined independently of the particle velocity.

[0078] Figure 6 Another embodiment of the device is shown, wherein the light source 2 is configured to project two light beams with different wavelengths λ1, λ2 respectively along the beam axis, the two light beams overlap in the projection plane xy and thus have a position-dependent intensity distribution and a position-dependent wavelength distribution, and wherein the detector is configured to detect at least one wavelength-dependent intensity of the measuring beam and output a wavelength-dependent intensity signal to an analysis and processing unit, wherein the analysis and processing unit is configured to determine the particle position within the measurement volume based on the wavelength-dependent intensity signal.

[0079] With the position-dependent wavelength distribution, in addition to the intensity of the measuring beam, other light properties can also be taken into account in order to be able to uniquely determine the particle properties. In particular, in addition to or as an alternative to the position-dependent polarization distribution, the position-dependent wavelength distribution can be used in order to be able to uniquely determine the particle position within the measurement volume. Figure 6 The embodiments of the intensity distribution and wavelength distribution shown mean that the light beam reflected or scattered by the particle in the form of the measuring beam can have at least two wavelength components, taking into account which allows the position of the particle in the projection plane to be determined uniquely and unambiguously.

[0080] The detector can have a plurality of photodiodes which are configured to be wavelength sensitive so that detected reflected beams with different wavelength components cause different signal amplitudes in the corresponding photodiodes. The wavelength-dependent signal can be evaluated using mathematical models, tables or characteristic curves to determine particle characteristics, in particular particle position.

Claims

1. A device (1) for characterizing particles, the device A light source (2), in particular a laser, is provided for projecting at least one light beam (4) along a beam axis (5), and A beam shaping optical unit (3) is arranged along the beam axis (5) and is designed to adjust a position-dependent intensity distribution of the light beam (4) in a measurement volume (6) extending in sections along the beam axis (5), and At least one detector (10) is configured to detect at least one measuring beam (8) reflected and / or scattered by the particle (7) when the particle (7) is located in the measuring volume (6) and to output at least one intensity signal to an evaluation unit, in, The evaluation unit is designed to determine a property of particles in the measurement volume based on the intensity signal. It is characterized in that The beam shaping optical unit (3) is designed to shape the position-dependent intensity distribution in a projection plane (xy) such that the intensity of the light beam is minimum along the outer contour (15) of an ellipse (11) and maximum at at least one point (14) within the ellipse (11), in particular at least at the center point of the surface of the ellipse (11), the projection plane extending transversely to the beam axis (5) within the measurement volume.

2. The device (1) according to claim 1, wherein: The beam shaping optical unit (3) is designed to adjust a position-dependent polarization distribution in the projection plane (xy), wherein along the vertical axis (H) of the ellipse (11) there is at least one first polarization (16) and a second polarization (17) with different polarization directions, and The detector (10) is designed to determine at least two intensities of the measuring beam (8) having the first polarization (16) and / or the second polarization (17) and to output two polarization-dependent intensity signals to the evaluation unit, and Therein, the evaluation unit is designed to ascertain the particle property, in particular the particle position, as a function of the at least two polarization-dependent intensity signals.

3. The device (1) according to claim 2, wherein: The beam shaping optical unit (3) is designed to generate the position-dependent polarization distribution in such a way that an angle of 180 degrees exists between the polarization direction of the first polarization (16) and the polarization direction of the second polarization (17), and At least one third polarization (18) is present along the vertical axis (H) of the ellipse (11), preferably in the region of the point of maximum intensity of the ellipse (11), wherein an angle of 90 degrees exists between the polarization direction of the first polarization (16) and the polarization direction of the third polarization and / or an angle of 90 degrees exists between the polarization direction of the second polarization (17) and the polarization direction of the third polarization.

4. The device (1) according to claim 3, wherein: The beam shaping optical unit (3) is designed to generate the position-dependent polarization distribution in such a way that a fourth polarization (19, 20) is present along the vertical axis (H) of the ellipse (11) and between the first polarization (16) and the third polarization (18) and / or between the second polarization (17) and the third polarization (18), wherein an angle of 45 degrees exists between the polarization direction of the fourth polarization (19, 20) and the polarization direction of the third polarization (18).

5. The device (1) according to claim 4, wherein: The detector is designed to determine polarization-dependent intensity components of the measuring beam (8) in at least two of the following polarizations: 0 degrees, 45 degrees, 90 degrees, 135 degrees.

6. A device (1) at least according to claim 2, wherein: The light source and / or the beam shaping optical unit are configured to generate at least two light beams having a phase difference, wherein the phase difference is 90 degrees in order to at least partially adjust the circular polarization in the projection plane (xy), Or wherein the phase difference is between 0 degrees and 90 degrees, or between 90 degrees and 180 degrees, so as to at least partially adjust the elliptical polarization in the projection plane (xy).

7. The device (1) according to any one of the preceding claims, wherein: The light source (2), in particular the laser (2), and / or the beam shaping optical unit (3) are designed to shape the position-dependent intensity distribution in the projection plane (xy) in such a way that the intensity is minimum along the two outer contours of the two ellipses (11, 11') and the intensity is maximum in the region of the vertical axes (H; H') of the two ellipses (11, 11'), the vertical axes (H, H') of the two ellipses (11, 11') being arranged in a V-shape, wherein the detector (10) is designed to detect the intensities of the two measuring beams (8) in a time-shifted manner, and wherein: The evaluation unit is designed to determine the position of a particle within the measurement volume (6) at least as a function of the time interval between the measured intensities of the two measurement beams (8).

8. The device (1) according to any one of the preceding claims, wherein: The light source (2), in particular the laser (2), and / or the beam shaping optical unit (3) are designed to shape the position-dependent intensity distribution in the projection plane in such a way that the intensity along the three outer contours of the three ellipses (11, 11', 11") is minimal and the intensity is maximal in the region of the vertical axes (H, H', H") of the three ellipses (11, 11', 11"), the vertical axes (H, H', H") of the three ellipses (11, 11', 11") being arranged in an N-shape, wherein the detector (10) is designed to detect the intensities of three measuring beams (8) in a time-shifted manner, and wherein: The evaluation unit is designed to determine the particle position within the measurement volume (6) as a function of two time intervals between the measured intensities of the three measurement beams (8) and in particular independently of the particle velocity.

9. The device (1) according to any one of the preceding claims, wherein: The light source (2), in particular the laser (2), and / or the beam shaping optical unit (3) are configured to project two light beams (4) with different wavelengths (λ1, λ2) along a beam axis (5), the two light beams overlapping in the projection plane (xy) and having the position-dependent intensity distribution and the position-dependent wavelength distribution. The detector (10) is designed to detect at least one wavelength-dependent intensity of the measuring beam (8) and to output a wavelength-dependent intensity signal to the evaluation unit, wherein: The evaluation unit is designed to determine the particle position within the measurement volume as a function of the wavelength-dependent intensity signal.

10. The device (1) according to any one of the preceding claims, wherein: The detector (10) has a spatial resolution within the measurement volume of from 5 micrometers to 0.1 micrometers, preferably from 3 micrometers to 1 micrometer, most preferably 1 micrometer.

11. The device (1) according to any one of the preceding claims, wherein: At least the light source (2), in particular the laser (2), and / or the beam shaping optical unit (3) are arranged in a non-movable manner in order to form the measurement volume (6) in a fixed position or wherein: The light source (2), in particular the laser (2), and / or the beam shaping optical unit (3) and / or the detector (10) are arranged movably in order to displace the measurement volume (6) by means of at least one scanning movement.

12. A method for characterizing a particle (7), wherein: Projecting the light beam (4) along a beam axis (5), The light beam (4) has a position-dependent intensity distribution in a measurement volume (6) extending in sections along the beam axis, and wherein the particle (7) to be characterized reflects or scatters the light beam (4) at least partially in the measurement volume (6) as a measurement beam (8), and determining a particle property in the measurement volume (6) based on at least one intensity of the measurement beam (8), It is characterized in that The position-dependent intensity distribution in a projection plane (xy), which preferably extends transversely to the beam axis (5) within the measurement volume, has an intensity that is minimum along the outer contour (15) of an ellipse (11) and maximum at at least one point (14) within the ellipse (11).

13. The method according to claim 12, wherein: The light beam (4) has a spatially dependent polarization distribution, and the particle property is ascertained as a function of the polarization-dependent intensity of the measurement beam (8).

14. The method according to claim 12 or 13, wherein: generating two light beams (4) with different wavelengths, said two light beams overlapping in said measurement volume, wherein the overlapping light beam has said position-dependent intensity distribution and said position-dependent wavelength distribution in said projection plane (xy), and Therein, properties of the particles in the measurement volume are determined as a function of the wavelength-dependent intensity of the measurement beam (8).

15. The method according to any one of claims 12 to 14, wherein: The position-dependent intensity distribution is generated in the projection plane (xy) in such a way that the intensity of the light beam (4) is minimum along the outer contours of three ellipses (11) and maximum in the region of the vertical axes (H, H', H") of the three ellipses (11), which are arranged in an N-shape. wherein the particle (7) to be characterized at least partially reflects or scatters the light beam (4) in the measurement volume (6) into three measurement beams (8), wherein the intensities of the three measurement beams are detected in a time-shifted manner, A particle property, in particular a particle position, within the measurement volume (6) is determined from two time intervals between measured intensities of the measurement beam (8) and preferably independently of the particle velocity.

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