Devices and methods for characterizing particles

Abstract

The present invention relates to an apparatus (10) and method for characterizing a particle (12) based on at least two light curtains (26A, 26B) and different intensity distributions, polarization distributions and / or wavelength distributions.

Description

Technical Field

[0001] This invention relates to an apparatus and method for characterizing one or more particles. Prior Technology

[0002] The devices and methods described above are generally known and used in various applications to determine particle characteristics, such as particle position, particle velocity, or particle size. For example, this can be used to monitor or regulate industrial manufacturing and processing processes.

[0003] DE102022123464.9 describes an apparatus for determining particle characteristics, comprising a light source by means of which a light beam is projected along a beam axis. Beam-shaping optics are arranged along the beam axis. The beam-shaping optics are designed to establish a position-dependent intensity distribution of the light beam within a measurement volume extending locally along the beam axis. Particles to be characterized located within the measurement volume reflect or scatter the light beam at least partially into a measurement beam. This measurement beam is detected by means of a detector that outputs an intensity signal to an evaluation unit. The evaluation unit is used to determine particle characteristics within the measurement volume based on the intensity signal. Summary of the Invention

[0004] The purpose of this invention is to provide an apparatus and method that bring higher accuracy to particle characterization.

[0005] The object of the present invention is achieved by a device having the features of claim 1. The present invention relates to a device for characterizing particles, comprising: at least one light source for projecting at least one first beam at least substantially parallel to a beam axis and at least one second beam at least substantially parallel to a beam axis, wherein the at least one first beam and the at least one second beam are arranged spaced apart from each other perpendicular to the first beam axis; at least one beam-shaping optics element arranged along the beam axis and designed to set position-dependent intensity distributions and / or position-dependent polarization distributions and / or position-dependent wavelength distributions of the first beam along a first screen plane and / or the second beam along a second screen plane in a measurement volume extending locally along the beam axis; and at least one detector designed to detect particles. A first measurement beam reflects and / or scatters a first beam of light and a second measurement beam reflects and / or scatters a second beam of light from the particles, and outputs at least one measurement signal to an evaluation unit; and the evaluation unit is designed to determine particle characteristics based on the first and second measurement beams, wherein the beam-shaping optics are designed with position-dependent intensity and polarization distributions in the first and / or second screen planes such that the intensity of the first and / or second beams is minimized along the outer contour of an ellipse and maximized at at least one point within the ellipse, and / or there are at least one first polarization and a second polarization with different polarization directions along the vertical axis of the ellipse of the first and / or second beams. The intensity and / or polarization distributions of the first beam along the first screen plane and the intensity and / or polarization distributions of the second beam along the second screen plane are different. Higher accuracy can be achieved in characterization due to the at least two beams and the at least two light curtains generated in the measurement volume. This accuracy is further improved due to the difference in the intensity and / or polarization distributions of the two beams or light curtains. If particles pass through the light curtains at the same location, the measurement beams can contain different intensities and / or different polarization directions. Using multiple light curtains ensures that the particle can be characterized even if the measured intensity and / or polarization direction appears multiple times within the light curtains. In this case, a second measurement beam serves as an additional allocation variable, allowing for a denser intensity distribution and / or a denser polarization distribution to be used within the light curtains. In this scenario, the intensity and / or polarization distribution can be set two or more times within the light curtains.

[0006] Using multiple light curtains also has the following advantages: the relative velocity of particles can be determined by the time difference between the first and second measuring beams.

[0007] One advantageous provision of this specification states that the light source and / or beam-shaping optical elements are designed such that the first beam and the second beam are parallel to each other and / or the first screen plane and the second screen plane are parallel to each other. Furthermore, the relative motion direction of the particles can be determined accordingly. Here, the positions of the particles at the first screen plane and the second screen plane are compared and combined to form a direction vector.

[0008] Another advantageous aspect of this specification states that the light source and / or beam shaping optical element is designed such that the first beam has a polarization distribution with a first rotation order and the second beam has a polarization distribution with a second rotation order, wherein the first rotation order and / or the second rotation order are not equal to 1.

[0009] In the context of this invention, "rotation order" should be understood as a measure of the spatial variation of the polarization plane or polarization direction of a light beam. The rotation order quantifies the frequency at which the polarization direction of the light beam rotates a full 180° along the height axis from the x-axis direction to the opposite direction (e.g., from horizontal to horizontal). When the polarization order is 0, the polarization plane or polarization direction is constantly oriented in one direction. When the polarization order is 1, the polarization plane or polarization direction rotates 180° once along the height extension of the beam. When the polarization order is greater than 1, the polarization plane or polarization direction rotates 180° several times along the height extension of the beam. The height extension here refers to the region of the beam used for measurement; further rotation of polarization may occur outside this region, but this is irrelevant.

[0010] It is conceivable that there might be an incomplete rotation of less than 180° in the polarization plane. In this case, according to mathematical laws, it can be rounded to the nearest integer. For example, the rotation order of a beam with a polarization plane rotated by 390° is 2 (390° / 180° = 2.17 is rounded down).

[0011] Preferably, the rotation order can be determined or generated using common methods known in the art, particularly by means of a polarizing beam splitter and a camera. Alternatively, the polarization direction can be determined by multiple measurements along the height axis using a polarimeter, thereby determining the rotation order of the beam. Here, the lower and upper ends of the area of ​​the beam used for measurement, as well as the points off-center between the lower and upper ends, can be measured. Based on the results of the point measurements, further measurements can be performed between two adjacent measurement points, which are then arranged off-center between these two measurement points. This process can be repeated until the rotation order of the beam can be deduced without doubt. If a sufficiently high rotation order is ensured, the process can alternatively be terminated. In the sense of this invention, "not equal to 1" should also be understood as meaning that the rotation of the polarization plane along the height axis is not within the range of 150° and 210°.

[0012] A design with at least one rotation order greater than 1 results in an increase in the density of rotational variations along the height axis. This also makes it more accurate to characterize particles.

[0013] Advantageously, the light source and / or beam-shaping optics are designed such that the first and second rotation orders are different. If the rotation order is greater than 1, the rotation direction (e.g., horizontal or right-handed) can appear multiple times along the beam's height axis. Therefore, it is impossible to reliably state the position of, for example, a particle using the measurement signal. In this case, the polarization distribution in the second light curtain is configured such that different polarization directions exist at that location. Thus, the accurate position of the particle can be inferred from the combination of the first and second measurement signals. Due to the higher rotation order of the first and / or second beams, higher overall measurement accuracy is achieved without reducing or increasing the measurement volume or light curtain.

[0014] A further advantage is that the light source and / or beam-shaping optics are designed such that the first and second rotation orders are coprime, i.e., they have no common divisor, particularly greater than 1. This ensures that repeating polarization directions in adjacent light curtains do not coincide. Therefore, particles can still be reliably characterized despite the repeating patterns in the light curtains.

[0015] One advantageous provision of this specification states that the light source and / or beam-shaping optical elements are designed such that the first rotation order and the second rotation order are each a different prime number. This further ensures that repeating polarization directions in adjacent light curtains do not coincide. Therefore, despite the repeating patterns in the light curtains, particles can still be reliably characterized.

[0016] Preferably, the light source and / or beam-shaping optics are designed such that the first rotation order differs from the second rotation order by 1. Therefore, a vernier caliper ("Nonius") can be used to make statements about the characterization using an additional light curtain or additional measurement signal, which are more accurate than statements made with the accuracy of a single measurement signal. Thus, the accuracy of an existing system with a single light curtain can also be improved by adding at least one additional light curtain.

[0017] One of the advantageous specifications in this specification states that the light source and / or beam shaping optical element is designed such that the first rotation order or the second rotation order is equal to 0.

[0018] Another advantageous provision of this specification is that the light source and / or beam shaping optical element are designed such that the polarization distributions of the first beam and the second beam differ in terms of polarization phase shift.

[0019] Advantageously, the beam-shaping optics incorporate a shaping element. This shaping element can produce at least locally linear or at least locally nonlinear polarization patterns, or is designed as a waveplate, particularly a vortex plate or S-waveplate. Preferably, the light source and / or the beam-shaping optics are designed such that the first and second beams are projected onto two different radial positions of the shaping element. Thus, at least two beams parallel to each other can be projected, which, where appropriate, already possess common or different polarization distributions.

[0020] One advantageous provision in this specification states that one detector is provided for all measurement beams or one detector is provided for each measurement beam. If the distance between the two particles to be characterized is large enough, multiple detectors can be used; otherwise, the measurement signals may overlap. If the distance is too small, a single detector can be used, in which the signals can be distinguished by different wavelengths. If multiple detectors are used, it may be necessary to guide the beams to each detector. Preferably, each detector has at least two photodetectors.

[0021] A further advantage is that the light source and / or beam-shaping optics are designed so that the first and second beams differ in wavelength, wherein interferometric elements, particularly dichroic mirrors, are arranged along the first and / or second measurement beams, especially along the measurement axes parallel to the measurement beams, to separate the first and second measurement beams. Therefore, multiple detectors can be used even if the measurement beams are close to each other. This structure is particularly advantageous for characterizing many particles arranged close together. In this case, the detectors can be spaced apart from each other, particularly at a distance greater than the distance between the two measurement beams.

[0022] Another advantageous embodiment of this specification specifies that the beam-shaping optical element has a birefringent element and / or a double prism for generating at least two beams parallel to each other. Preferably, the birefringent element can be a birefringent crystal, particularly an angled plane parallel plate, designed to separate and parallelize the beams, providing high polarization stability or polarization scattering. Here, a phase shift in the polarization distribution is provided, which is useful for characterizing particles. Preferably, a double prism is provided to angle the beams, wherein another double prism or lens is provided after the first double prism for parallelization.

[0023] Advantageously, the evaluation unit is further configured to determine particle characteristics based on the polarization directions of the first and second measurement beams.

[0024] The object of the present invention is also achieved by a method having the features of claim 14. The present invention relates to a method for characterizing particles, comprising the following steps: projecting a first beam and a second beam parallel to a beam axis, wherein, in a measurement volume, the first beam along a first screen plane and the second beam along a second screen plane have position-dependent intensity distributions and / or position-dependent polarization distributions and / or position-dependent wavelength distributions; using the first beam reflected and / or scattered by the particles as a first measurement beam, and using the second beam reflected and / or scattered by the particles as a second measurement beam; determining particle characteristics within the measurement volume based on the first and second measurement beams, wherein the intensity distribution of the first beam along the first screen plane and the intensity distribution of the second beam along the second screen plane are different, and / or wherein the polarization distribution of the first beam along the first screen plane and the polarization distribution of the second beam along the second screen plane are different, and / or wherein the wavelength distribution of the first beam along the first screen plane and the wavelength distribution of the second beam along the second screen plane are different.

[0025] Advantageously, particle characteristics are determined based on the polarization direction of the first and / or second measurement beams.

[0026] One advantageous embodiment of this specification specifies that particle characteristics, particularly particle velocity and / or particle acceleration, are determined based on the time offset of a first measuring beam and a second measuring beam. Particularly advantageous is the ability to simultaneously detect particle velocity and particle position using this device and / or method. Therefore, the device can be configured for detecting both particle velocity and particle position. Simple Explanation of the Diagram

[0027] Further advantages, features, and details will become apparent from the following description, wherein various embodiments of the invention are illustrated with reference to the figures. Hereinafter, the features mentioned in the claims and specification may individually or in any combination constitute the essence of the invention.

[0028] In the diagram:

[0029] Figure 1 is a schematic diagram of the apparatus for characterizing particles according to the present invention;

[0030] Figure 2 shows a cross-sectional view of a beam with position-dependent intensity and polarization distributions;

[0031] Figure 3 shows two graphs, each with polarization-dependent intensity distributions, where the rotation order is 1, and the polarization distributions are phase-shifted.

[0032] Figure 4 shows two images, each with polarization-dependent intensity distributions. The first beam has a rotation order of 1, and the second beam has a rotation order of 7.

[0033] Figure 5 shows two images, each with polarization-dependent intensity distributions. The first beam has a rotation order of 6, and the second beam has a rotation order of 7.

[0034] Figure 6 shows two images, each with polarization-dependent intensity distributions. The first beam has a rotation order of 0, while the second beam has a rotation order of 1.

[0035] Figure 7 shows cross-sectional views of two parallel beams with two position-dependent intensity distributions. Implementation

[0036] According to Figure 1, the device 10 for characterizing particle 12 has a light source 14, particularly in the form of a laser, and a beam-shaping optical element 16 with a vortex plate and a cylindrical lens.

[0037] Light source 14 is used to generate an output beam 18 parallel to the beam axis 22. Beam shaping optics 16 splits the beam 20 into two or more beams 20 parallel to the beam axis 22. Alternatively, light source 14 can also independently generate two or more such beams 20, thus eliminating the need for separation in beam shaping optics 16.

[0038] The light beam 20 is partially used to measure the volume 24. For this purpose, each of the light beams 20 forms a light curtain 26 through which the particle 12 to be characterized passes. A first light curtain 26A and a second light curtain 26B are shown in Figure 1. During relative motion between the particle 12 and the device 10, the particle 12 passes through the light curtain 26, wherein the path of motion of the particle 12 is inclined, preferably perpendicular, to the light curtain 26. It is conceivable that the device 10 and / or the particle 12 move. According to Figure 1, the particle 12 is shown in the position in front of the first light curtain 26A, in the first light curtain 26A, and in the second light curtain 26B. Preferably, the light source 14 and / or the beam-shaping optics 16 are configured such that the first light curtain 26A and the second light curtain 26B are parallel to each other according to Figure 7.

[0039] The first light curtain 26A and the second light curtain 26B each have position-dependent intensity distributions and position-dependent polarization distributions. Example, the polarization-dependent intensity curves of the first light curtain 26A and the second light curtain 26B are shown in Figures 3 to 6.

[0040] Particles 12 located in the measurement volume 24, particularly in the first light curtain 26A and the second light curtain 26B, reflect and / or scatter corresponding beams 20 in the form of measurement beams 28. The first measurement beam 28A is generated by particles 12 in the first light curtain 26A, and the second measurement beam 28B is generated by particles 12 in the second light curtain 26B. They are each collected in one or more beam shaping elements 30 and selectively fed to one or more detectors 32. The beam shaping elements 30 may be designed as condenser lenses or condenser mirrors and / or interferometers, particularly dichroic mirrors. The detectors 32 preferably form a small angle with respect to the measurement volume 24 and the light source 14. Preferably, the detectors 32 and the light source 14 are designed to be fixed in position relative to each other.

[0041] The measurement beam 28 has multiple polarization-dependent intensities, which can be detected by means of at least one detector 32. The desired particle position within the measurement volume 24 can be determined by an evaluation unit 34, which may be designed alone or integrated into the detector 32, based on the intensity of at least one polarization-dependent component of the measurement beam 28.

[0042] According to Figure 1, particle 12 passes through the first light curtain 26A at time t1, causing detector 32 to detect the first measurement beam 28A at time t2, and passes through the second light curtain 26B at time t3, causing detector 32 to detect the second measurement beam 28B at time t4. Alternatively, it is conceivable that the first light curtain 26A is arranged behind the second light curtain 26B along the direction of movement of particle 12. Evaluation unit 34 is configured to generate a first intensity signal by the first measurement beam 28A and a second intensity signal by the second measurement beam 28B, each representing the position of particle 12 within the light curtain 26. Using multiple light curtains 26 facilitates improved accuracy in characterizing particle 12. This occurs when particle 12 impacts the same position of the light curtains, particularly when moving perpendicular to the light curtain 26. Furthermore, evaluation unit 34 is preferably configured to detect the position of particle 12 within the corresponding light curtain 26A based on the measurement beam 28, thereby determining its direction of movement. Furthermore, the evaluation unit 34 is preferably configured to determine the particle velocity of particle 12 when the distance between the light curtains 26 is known based on the measurement beam 28 and the time difference (Δt = t4 - t2) between the detected measurement beams 28. The distance between the light curtains 26 is preferably chosen such that only one particle 12 is positioned in the measurement volume 24 between time points t1 and t3, specifically between the first light curtain 26A and the second light curtain 26B. Characterization of particle 12 is preferably performed instantaneously. Preferably, this distance is in the range between 50 μm and 10 mm, more preferably between 50 μm and 7 mm, and more preferably between 50 μm and 1 mm.

[0043] According to Figure 2, the beam 20 in the first screen plane 27A (in which the first light curtain 26A is arranged) and / or the second screen plane 27B (in which the second light curtain 26B is arranged) essentially presents the shape of an ellipse 36 with two axes of symmetry. Figure 2 shows, for example, the polarization distribution of the second light curtain 26B, as shown below, according to Figure 3. The height dimension 38 of the ellipse 36 along the vertical axis H perpendicular to the beam axis 22 is greater than its width dimension 40 along the width axis B, which is perpendicular to both the vertical axis H and the beam axis 22. The vertical axis H is preferably vertical, and the width axis B is preferably horizontal. The intensity of the beam 20 is distributed such that it is maximum at the midpoint 42 of the surface of the ellipse 36 and steadily decreases toward the outer contour 44 of the ellipse 36, particularly minimum in the considered region at the outer contour 44 of the ellipse 36. Within the ellipse 36, a two-dimensional intensity distribution exists in a plane perpendicular to the curtain planes 27A and 27B, which preferably corresponds to a Gaussian intensity distribution. In other words, the intensity has a continuous orientation in the region between the surface midpoint 42 and the surrounding outer contour 44, wherein the intensity decreases radially from the surface midpoint 42 toward the outer contour 44. Other intensity distributions of the beam 20 are also conceivable, such as Laplace, Logistic, or Cauchy distributions, wherein the beam 20 may have the same or different intensity distributions.

[0044] This intensity distribution allows the beam 20 to be reflected at different intensities along the vertical axis H of the ellipse 36 in the form of a measurement beam 28. By measuring the intensity of the measurement beam 28, particle characteristics can be determined with high precision. If the particle characteristic to be determined is particle position, it is advantageous to consider that the intensity of the measurement signal can also vary according to the particle size. Therefore, the embodiment of the intensity distribution shown in FIG2 specifies that the beam shaping optics 16 generates a position-dependent polarization distribution with a rotation order N=1, indicated by arrows 46, 48, 50, 52, and 54 in FIG2. In this case, there are a first polarization 46 and a second polarization 48 along the vertical axis H, which are spaced apart from each other along the vertical axis H of the ellipse 36, and their polarization directions are at an angle of 180 degrees to each other. A third polarization 50 exists in the region of the midpoint 42 of the surface, whose polarization direction has a polarization angle of 90 degrees with the polarization directions of the first polarization 46 and the second polarization 48, respectively. A fourth polarization 52 exists between the first polarization 46 and the third polarization 50, with its polarization direction at a 45-degree angle relative to the polarization direction of the third polarization 50. A fifth polarization 54 exists between the second polarization 48 and the third polarization 50, also with a 45-degree angular difference relative to the third polarization 50. Contrary to the illustration shown, the position-dependent polarization distribution has a continuous orientation along the vertical axis H and includes discretely displayed polarizations.

[0045] If particle 12 is located in the projection plane of the corresponding light screen 26 and in the region of the vertical axis H of the ellipse 36, the corresponding beam 20 is reflected such that the measurement beam 28 has multiple intensity portions with different polarizations. Taking these polarization-related intensity portions into account makes it possible to determine the unique position of particle 12 within the light screen 26 or the projection plane.

[0046] According to Figure 3, the first beam 20 (top) for the first light curtain 26A and the second beam 20 (bottom) for the second light curtain 26B have multiple position-dependent intensity curves. Each of these intensity curves describes the polarization-dependent intensity of the beam 20 along the vertical axis H of the ellipse 36 in its projection plane. In this case, the first intensity curve 56 corresponds to the position-dependent intensity of the beam 20 with first polarization 46 and second polarization 48 according to Figure 2. The polarization directions of polarizations 46 and 48 have an angle of 180 degrees, making the polarization filter permeable to light with polarizations 46 and 48. The second intensity curve 58 corresponds to the position-dependent intensity of the beam 20 with third polarization 50 according to Figure 2. The third intensity curve 60 corresponds to the position-dependent intensity of the beam 20 with fourth polarization 52 according to Figure 2. The fourth intensity curve 62 corresponds to the position-dependent intensity of the beam 20 with fifth polarization 54 according to Figure 2. From Figure 3, it can be seen that the intensity distributions of the two beams 20 are designed to be the same, and the polarization distributions of the two beams 20 are designed to be different. In the second beam 20, intensity curves 56 and 58 are designed to be symmetrical. In the second beam 20, intensity curves 60 and 62 are designed to be asymmetrical, and in the first beam 20, intensity curves 56, 58 and 60, 62 are designed to be asymmetrical.

[0047] If particle 12 is located on the projection plane of beam 20, which corresponds to the imaging plane of FIG2, the reflected measurement beam 28 has multiple polarization-dependent intensities, which depend on the y-position of particle 12 and correspond to the intensity curves 56, 58, 60, and 62 according to FIG3. For example, if particle 12 is located at a height of 0 μm along the y-axis, the measurement beam 28 has a dominant intensity portion, which corresponds to the first intensity curve 56 and has a corresponding first polarization 46. Meanwhile, the measurement beam 28 in this example has a less distinct intensity portion, which corresponds to the third intensity curve 60 and the fourth intensity curve 62 and has corresponding fourth polarization 52 and fifth polarization 54. In other words, at the y-position of 0 μm, the first polarization 46 according to FIG2 is dominant; however, this first polarization can be represented by the linear superposition of equal portions of the second polarization 48 and the third polarization 50 of FIG2.

[0048] By measuring the polarization-related intensity using detector 32, this intensity can be assigned to a unique position of particle 12 along the y-axis, for example, using a mathematical model or table. The asymmetric orientation of the intensity curve in this case particularly allows for a unique difference between the two particle positions along the y-axis.

[0049] Detector 32 is configured to determine the polarization direction. In the embodiment of device 10 shown in FIG. 1, the measurement beam is split into two beams independently of polarization in a beam shaping element 30 in the form of a so-called 50:50 beam splitter. Along one of the optical paths, a polarization beam splitter is arranged behind the beam splitter along that path, and a photodiode (photodiode 1 and 2) is arranged in each output path. Along the other optical path, a polarization rotator element (e.g., a λ / 2 plate) for polarization rotation of 45° is arranged, and a polarization beam splitter is also arranged behind it, and a photodiode (photodiode 3 and 4) is arranged in each output path. The photodiode system is designed to detect different polarization components. The first photodiode 1 is designed here to detect the first polarization 46 and the second polarization 48 according to FIG. 2. The second photodiode 2 is designed to detect the third polarization 50 according to FIG. 2. Photodiodes 3 and 4 are designed to detect the fourth polarization 52 and the fifth polarization 54 according to FIG. 2. When the separated measurement beam 28 is detected, each photodiode outputs an electrical signal corresponding to the intensity of the measured light portion of one of the aforementioned polarizations. The evaluation of the signal is performed in the evaluation unit 34, for example by means of the mathematical model mentioned above. In the embodiment of the device 10 shown in FIG. 1, the measurement beam is split into two beams independently of polarization in a beam shaping element 30 in the form of a so-called 50:50 beam splitter. Two photodiodes are arranged along the optical path behind the beam splitter, and these photodiode systems are designed to detect different polarization components. The first photodiode is designed to detect the first polarization 46, the second polarization 48, and the third polarization 50 according to FIG. 2. The second photodiode system is designed to detect the fourth polarization 52 and the fifth polarization 54 according to FIG. 2. When the separated measurement beams 28 are detected, each photodiode outputs an electrical signal corresponding to the intensity of the measured portion of light in one of the aforementioned polarizations. The signal evaluation is performed in the evaluation unit 34, for example, using the mathematical model mentioned above.

[0050] Figure 4 shows alternative intensity and polarization distributions for beam 20. The first beam 20 has the same symmetrical intensity and polarization distribution as the second beam 20 according to Figure 3. The second beam 20 has an intensity and polarization distribution with a rotation order N=7. The first beam 20 has a rotation order N=1.

[0051] "Rotation order" represents a measure of the spatial variation of the polarization plane or polarization direction of beam 20. The rotation order quantifies the frequency at which the polarization direction of beam 20 rotates a full 180° along the height axis from the x-axis to the opposite direction (e.g., from the left horizontal of the first polarization 46 to the right horizontal of the second polarization 48). When the polarization order is 0, the polarization plane or polarization direction is constantly oriented in one direction, as shown in Figure 6 for the first beam 20. When the polarization order is 1, the polarization plane or polarization direction rotates 180° once along the height extension of beam 20, as shown in Figure 3 for both beams 20 and Figures 4 and 6 for the first beam 20. When the polarization order is greater than 1, the polarization plane or polarization direction rotates 180° multiple times along the height extension of beam 20, as shown in Figures 4 and 5 for the second beam 20 and Figure 5 for the first beam 20. It is conceivable that there may be incomplete rotations of less than 180° of the polarization plane. In such cases, according to mathematical laws, the value can be rounded to the nearest integer. For example, the rotation order of beam 20, which has its polarization plane rotated by 390°, is 2 (390° / 180° = 2.17 is rounded down). Alternatively, the rotation order can be rounded in increments of 0.5 or 0.1.

[0052] A larger rotation order results in a greater change in polarization direction as the particle moves along the polarization change axis. This change axis has a direction perpendicular to the axis H. Therefore, the position of the particle in the projection plane can be detected with greater accuracy by using the polarization angle. In other words, a larger rotation order N results in greater resolution.

[0053] As described in Figure 3, a rotation order greater than 1 causes the rotation direction (e.g., horizontal) to appear multiple times along the height axis H of the beam 20. Therefore, it is impossible to make a reliable statement about the position of, for example, particle 12, using the measurement signal from the measuring beam. Using the measuring beam 28, the measured polarization may allow inference of multiple positions within the second light curtain 26B. In this case, the polarization distribution in the first light curtain 26A is configured such that different polarization directions exist at these positions. Therefore, the accurate position of particle 12 can be inferred from the combination of the first and second measurement signals. Due to the higher rotation order of the first and / or second beams 20, higher overall measurement accuracy is achieved without reducing or increasing the measurement volume or the light curtain 26.

[0054] According to Figure 5, the first beam 20 has a rotation order of N=6, and the second beam 20 has a rotation order of N=7, which corresponds to a vernier scale ("Nonius"). Therefore, measurement accuracy can be further improved. According to Figure 6, the first beam 20 has a rotation order of N=0, and the second beam 20 has a rotation order of N=1. In Figure 3, both the first beam 20 and the second beam 20 have a rotation order of N=1. As an additional or alternative to the rotation order, the first beam and the second beam 20 may also differ in intensity distribution or phase shift, as shown in Figure 3.

[0055] The light source 14 may be further designed to project two beams 20 with different wavelengths λ1 and λ2 along the beam axis 22, which overlap in the projection plane where appropriate and have position-dependent intensity distribution and position-dependent wavelength distribution and, in particular, position-dependent polarization distribution. The detector 32 is designed to detect at least one wavelength-dependent intensity of the measurement beam 28 and output a wavelength-dependent intensity signal to the evaluation unit 34, which is designed to determine the particle position within the measurement volume 24 based on the wavelength-dependent intensity signal.

[0056] By utilizing a position-dependent wavelength distribution, in addition to the intensity of the measurement beam 28, another optical property can be considered to uniquely determine the particle characteristics. As an addition to or alternative to the position-dependent polarization distribution, a position-dependent wavelength distribution can be specifically used to uniquely determine the particle position within the measurement volume 24. The beam 20, having both intensity and wavelength distributions, results in the beam 20, as the measurement beam 28, being reflected or scattered by the particle 12, having at least two wavelength components. Taking these into account makes it possible to uniquely determine the position of the particle 12 in the projection plane. Here, the second light curtain 26B also improves the accuracy of position determination.

[0057] Detector 32 may have multiple photodiodes designed to be wavelength-sensitive, or multiple wavelength-dependent beam splitters, such that detected reflected beams with different wavelength components result in different signal amplitudes for the corresponding photodiodes. The evaluation of the wavelength-dependent signals can be performed using mathematical models, tables, or characteristic curves to determine particle characteristics, particularly particle positions. In this case, beam shaping element 30 may have interferometric elements, particularly dichroic mirrors, allowing the measurement signal to be directed to different detectors 32 using different wavelengths. It is also conceivable that the two light curtains 26A and 26B differ due to different wavelengths λ1 and λ2.

[0058] When using different wavelengths, the separation of beam 20 can be alternatively achieved by means of refraction / diffraction methods, such as prisms or diffraction gratings.

[0059] It is advantageous to use a flat-top beam for beam 20 because such flat-top beams do not have a reduced signal-to-noise ratio towards the end of the light curtain 26. Flat-top beams can be used in all the aforementioned embodiments.

[0060] B: Width Measurement H: Height dimension N: Rotation order 10: Device 12: Particles 14: Light source 16: Beam shaping optical elements 18: Output beam 20: Beam 22: Beam axis 24: Measuring volume 26: Light Curtain 26A: First Light Curtain 26B: Second Light Curtain 27A: Act I Plane 27B: Act II Plane 28: Measuring the beam 28A: First measuring beam 28B: Second measuring beam 30: Beam shaping element 32: Detector 34: Evaluation Unit 36: Oval 38: Height dimension 40: Width dimension 42: Midpoint of the surface 44: Outer contour 46: First polarization 48: Second polarization 50: Third polarization 52: Fourth polarization 54: Fifth Polarization 56: First intensity curve 58: Second intensity curve 60: Third intensity curve 62: Fourth Intensity Curve

Claims

1. An apparatus (10) for characterizing particles (12), comprising: At least one light source (14) for projecting at least one first beam (20) parallel to the beam axis (22) and at least one second beam (20) parallel to the beam axis (22), wherein the at least one first beam (20) and the at least one second beam (20) are arranged perpendicular to the first beam axis (22) and spaced apart from each other; at least one beam shaping optics (16) arranged along the beam axis (22) and designed to set the position-dependent intensity distribution and / or position-dependent polarization distribution of the first beam (20) along the first screen plane (27A) and the second beam (20) along the second screen plane (27B) in a measurement volume (24) extending locally along the beam axis (22). At least one detector (32) is configured to detect a first measurement beam (28A) of the first beam (20) reflected and / or scattered by the particle (12) and a second measurement beam (28B) of the second beam (20) reflected and / or scattered by the particle (12), and to output at least one measurement signal to an evaluation unit (34), and the evaluation unit (34) is configured to determine particle characteristics based on the first measurement beam (28A) and the second measurement beam (28B); wherein the beam shaping optics (16) is configured to such a position-dependent intensity distribution and / or a position-dependent polarization distribution in the first screen plane (27A) and / or the second screen plane (27B). The intensity of the first beam and / or the second beam (20) is minimized along the outer contour (44) of the ellipse (36) and maximized at at least one point within the ellipse (36), and / or there exists at least one first polarization (46) and a second polarization (48) with different polarization directions along the vertical axis of the ellipse (36) of the first beam and / or the second beam (20); wherein the intensity distribution of the first beam (20) along the first screen plane (27A) is different from the intensity distribution of the second beam (20) along the second screen plane (27B), and / or wherein the polarization distribution of the first beam (20) along the first screen plane (27A) is different from the polarization distribution of the second beam (20) along the second screen plane (27B).

2. The apparatus (10) of claim 1, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first beam (20) and the second beam (20) are parallel to each other and / or the first screen plane (27A) and the second screen plane (27B) are parallel to each other.

3. The apparatus (10) of claim 1 or 2, wherein the light source (14) and / or the beam shaping optical element (16) are designed such that the first beam (20) has a polarization distribution with a first rotation order and the second beam (20) has a polarization distribution with a second rotation order, wherein the first rotation order and / or the second rotation order is not equal to 1.

4. The apparatus (10) of claim 3, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first rotation order is different from the second rotation order.

5. The apparatus (10) of claim 3, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first rotation order and the second rotation order are coprime.

6. The apparatus (10) of claim 3, wherein the light source (14) and / or the beam shaping optical element (16) are designed such that the first rotation order and the second rotation order are each a different prime number.

7. The apparatus (10) of claim 3, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first rotation order differs from the second rotation order by 1.

8. The apparatus (10) of claim 3, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first rotation order or the second rotation order is equal to 0.

9. The apparatus (10) of claim 1 or 2, wherein the light source (14) and / or the beam shaping optical element (16) are designed such that the polarization distributions of the first beam (20) and the second beam (20) are different in terms of polarization phase shift.

10. The apparatus (10) of claim 1 or 2, wherein the beam shaping optics (16) has a shaping element, wherein the shaping element is configured to generate at least a locally linear or nonlinear polarization pattern, and / or wherein the shaping element is designed as a waveplate, particularly a vortex plate or an S-waveplate, and wherein, in particular, the light source (14) and / or the beam shaping optics (16) are designed such that the first beam (20) and the second beam (20) are projected onto two different radial positions of the shaping element.

11. The apparatus (10) of claim 1 or 2, wherein the light source (14) and / or the beam shaping optical element (16) are designed such that the first beam (20) and the second beam (20) are different in wavelength, wherein interference elements, particularly dichroic mirrors, are provided along the first measuring beam (28A) and / or the second measuring beam (28B) for separating the first measuring beam (28A) and the second measuring beam (28B).

12. The apparatus (10) of claim 1 or 2, wherein the beam shaping optics (16) has a birefringent element and / or a double prism for generating at least two beams (20) that are parallel to each other.

13. The apparatus of claim 1 or 2, wherein the evaluation unit (34) is further configured to determine particle characteristics based on the polarization directions of the first measurement beam (28A) and the second measurement beam (28B).

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