Device and method for characterizing a particle

Abstract

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

Description

[0001] Device and method for characterizing a

[0002] particles

[0003] Description

[0004] The invention relates to a device and a method for characterizing one or more particles.

[0005] A device and a method of the types mentioned above are generally known and are used in various applications to determine a particle characteristic, such as a particle position, a particle velocity, or a particle size. This can be used, for example, to monitor or control industrial manufacturing and processing processes.

[0006] A device for determining particle characteristics is described in DE102022123464.9 and comprises a light source by means of a light beam which is projected along a beam axis. Beam shaping optics are arranged along the beam axis. The beam shaping optics are designed to set a location-dependent intensity distribution of the light beam in a measuring volume which extends sectionally along the beam axis. A particle to be characterized, which is located in the measuring volume, reflects or scatters the light beam at least partially as a measuring beam. This measuring beam is detected by means of a detector which outputs an intensity signal to an evaluation unit. The evaluation unit serves to determine the particle characteristics within the measuring volume as a function of the intensity signal.

[0007] The invention is based on the object of providing a device and a method which bring about a higher accuracy in the characterization of a particle.

[0008] The object underlying the invention is achieved by a device having the features of claim 1. The invention is directed to a device for characterizing a particle, comprising: at least one light source for projecting at least one first light beam running at least substantially parallel to a beam axis and at least one second light beam running at least substantially parallel to the beam axis, wherein the at least one first light beam and the at least one second light beam are arranged at a distance from one another perpendicular to the first beam axis, at least one beam shaping optics which is arranged along the beam axis and is designed to, in a measuring volume which extends in sections along the beam axis,to set a location-dependent intensity distribution and / or a location-dependent polarization distribution and / or a location-dependent wavelength distribution of the first light beam along a first curtain plane and / or of the second light beam along a second curtain plane, at least one detector which is designed to detect a first measuring beam reflected and / or scattered by the particle and a second measuring beam reflected and / or scattered by the particle and to output at least one measurement signal to an evaluation unit, the evaluation unit which is designed to determine a particle characteristic depending on the first measuring beam and the second measuring beam, wherein the beam shaping optics is designed,to form the location-dependent intensity distribution and / or the location-dependent polarization distribution in the first curtain plane and / or the second curtain plane such that an intensity of the first and / or second light beam is minimal along an outer contour of an oval and maximal at least at one point within the oval, and / or that along a vertical axis of the oval of the first and / or second light beam, at least a first polarization and a second polarization with different polarization directions are present. The intensity distribution and / or the polarization distribution of the first light beam along the first curtain plane and the second light beam along the second curtain plane differ. Due to the at least two light beams and the at least two light curtains generated therefrom in the measurement volume, a higher accuracy in the characterization can be achieved. This is further increased bythat the intensity distribution and / or the polarization distribution of the two light beams or light curtains differ. If a particle passes through the light curtains at the same position, the measuring beams can have a different intensity and / or a different polarization direction. The plurality of light curtains ensures that the particle can be characterized even if the measured intensity and / or polarization direction occurs multiple times in one light curtain. In this case, the second measuring beam serves as an additional assignment variable, so that a denser intensity distribution and / or a denser polarization distribution can be used in the light curtains. In this case, the intensities and / or polarization distributions can be provided twice or multiple times in one light curtain.

[0009] The use of several light curtains also has the advantage that the relative speed of the particle can be determined based on the time difference between the first and second measuring beams.

[0010] An advantageous aspect of the description provides that the light source and / or the beam-shaping optics are designed such that the first light beam and the second light beam run parallel to one another and / or that the first curtain plane and the second curtain plane run parallel to one another. Furthermore, the relative direction of movement of the particle can also be determined in this way. The position of the particle at the first curtain plane and at the second curtain plane are compared with one another and combined to form a directional vector. A further advantageous aspect of the description provides that the light source and / or the beam-shaping optics are designed such that the first light beam has a polarization distribution with a first rotation order and the second light beam 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.

[0011] For the purposes of the invention, a "rotation order" is understood to be a measure for a light beam which defines the spatial variation of the polarization plane or polarization direction. The rotation order quantifies the frequency with which the polarization direction of a light beam along the height axis completes a full 180° rotation from an orientation along an x-axis to an orientation opposite the x-axis, such as from horizontal to horizontal. With a polarization order of 0, the polarization plane or polarization direction is constantly oriented in one orientation. With a polarization order of 1, the polarization plane or polarization direction rotates 180° along the height extension of the light beam once. With a polarization order greater than 1, the polarization plane or polarization direction rotates 180° along the height extension of the light beam several times.The height extension refers to the area of ​​the beam that is used for the measurement - outside this area a further rotation of the polarization can take place, but this is not relevant.

[0012] It is, of course, conceivable that incomplete rotations of the polarization plane by 180° may occur. In this case, the laws of mathematics allow the rotation to be rounded up or down to the nearest whole number. For example, a light beam with a rotation of the polarization plane of 390° then has a rotation order of 2 (rounded down from 390° / 180° = 2.17).

[0013] The rotation order can preferably be determined or generated using methods commonly known in the art, in particular using a polarization beam splitter and cameras. Alternatively, a polarimeter can be used to take several measurements along the height axis to determine the direction of polarization, and these measurements can be used to determine the rotation order of the light beam. The lower and upper ends of the region of the light beam used for the measurement, as well as a point between the lower and upper ends, which is arranged off-center, can be measured. Depending on the result of the point measurement, a further measurement can be taken between two adjacent measuring points, which is in turn arranged off-center between these two. The process can be repeated until the rotation order of the light beam can be determined beyond doubt.Alternatively, the process can be aborted if a sufficiently high rotation order is ensured. For the purposes of the invention, "unequal to 1" also means that the rotation of the polarization plane along the elevation axis is not in the range between 150° and 210°.

[0014] The formation of at least one rotation order greater than 1 causes the density of the rotation change along the height axis to increase. This also results in greater precision in the characterization of the particle. It is advantageous if the light source and / or the beam shaping optics are designed such that the first rotation order and the second rotation order are different. If a rotation order is greater than 1, a rotation direction (e.g. horizontal or horizontal right) can occur multiple times along the height axis of the light beam. This means that no reliable statement can be made, for example, about the position of the particle based on one measurement signal. In this case, the polarization distribution in the second light curtain is set such that different polarization directions are present at this position.The combination of the first and second measurement signals allows the exact position of the particle to be determined. Due to the higher rotational order of the first and / or second light beam, a higher overall measurement accuracy is achieved without reducing or enlarging the measurement volume or the light curtain.

[0015] It is further advantageous if the light source and / or the beam-shaping optics are designed such that the first rotation order and the second rotation order are coprime, i.e., they do not have a common divisor, in particular a divisor greater than 1. This ensures that repeating polarization directions in adjacent light curtains are not aligned. Despite repeating patterns in a light curtain, the particle can thus be reliably characterized.

[0016] An advantageous aspect of the description provides that the light source and / or the beam-shaping optics are configured 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 are not aligned. Despite repeating patterns in a light curtain, the particle can thus continue to be reliably characterized.

[0017] Preferably, the light source and / or the beam-shaping optics are configured such that the first rotation order and the second rotation order differ by 1. Accordingly, a Vernier scale ("nonius") can be used to make more precise characterization statements using the additional light curtain or the additional measurement signal than is possible with the accuracy of the single measurement signal. Accordingly, the accuracy of existing systems with a light curtain can also be improved by adding at least one additional light curtain.

[0018] An advantageous aspect of the description provides that the light source and / or the beam-shaping optics are designed such that the first rotation order or the second rotation order is equal to 0.

[0019] A further advantageous aspect of the description provides that the light source and / or the beam-shaping optics are designed such that the polarization distribution of the first light beam and the second light beam differ with regard to a phase shift of the polarization.

[0020] It is advantageous if the beam shaping optics have a shaping element. The shaping element can generate an at least partially linear polarization pattern or at least partially non-linear polarization pattern or can be designed as a wave plate, in particular a vortex plate or S-wave plate. Preferably, the light source and / or the beam shaping optics are designed such that the first light beam and the second light beam are projected onto two different radial positions of the shaping element. Accordingly, at least two light beams running parallel to one another can be projected, which may already have a common or different polarization distribution.

[0021] An advantageous aspect of the description provides that one detector is provided for all measuring beams or one detector per measuring beam. If the distance between two particles to be characterized is sufficiently large, several detectors can be used, since otherwise the measuring signals could overlap. If the distance is too small, one detector can be used, in which case a differentiation of the signals across different wavelengths is possible. If several detectors are used, a beam line to the individual detectors may be necessary. Each detector preferably has at least two photodetectors.

[0022] It is furthermore advantageous if the light source and / or the beam-shaping optics are designed such that the first light beam and the second light beam differ in terms of wavelength, wherein an interference element, in particular a dichroic mirror, is provided along the first measuring beam and / or the second measuring beam, in particular along a measuring axis running parallel to the measuring beams, for separating the first measuring beam and the second measuring beam. Accordingly, a plurality of detectors can be used, even if the measuring beams run close to one another. This design is particularly advantageous for characterising many particles arranged close to one another. In this case, the detectors can be arranged at a distance from one another, in particular further than the distance between the two measuring beams.

[0023] A further advantageous aspect of the description provides that the beam shaping optics has a birefringent element and / or a biprism for generating at least two parallel light beams. The birefringent element can preferably be designed as a birefringent crystal for separating and parallelizing the light beam, in particular as an angled, plane-parallel plate, whereby a high polarization stability or polarization scattering is achieved. This provides a phase shift of the polarization distribution, which is useful for characterizing the particles. The biprism is preferably provided for angling the light beams, whereby a further biprism or a lens is provided downstream for parallelizing.

[0024] It is advantageous if the evaluation unit is further configured to determine a particle characteristic as a function of a polarization direction of the first measuring beam and the second measuring beam.

[0025] The object underlying the invention is also achieved by a method with the features of claim 14. The invention is directed to a method for characterizing a particle, comprising the following steps: projecting a first light beam and a second light beam parallel to a beam axis, wherein in a measuring volume the first light beam along a first curtain plane and the second light beam along a second curtain plane has a location-dependent intensity distribution and / or a location-dependent polarization distribution and / or a location-dependent wavelength distribution; reflecting and / or scattering the first light beam from the particle as a first measuring beam and the second light beam from the particle as a second measuring beam;Determining a particle characteristic of the particle within the measuring volume as a function of the first measuring beam and the second measuring beam, wherein the intensity distribution of the first light beam along the first curtain plane and the second light beam along the second curtain plane differ and / or wherein the polarization distribution of the first light beam along the first curtain plane and the second light beam along the second curtain plane differ and / or wherein the wavelength distribution of the first light beam along the first curtain plane and the second light beam along the second curtain plane differ .;

[0026] It is advantageous if the particle characteristic is determined as a function of a polarization direction of the first measuring beam and / or the second measuring beam.

[0027] An advantageous aspect of the description provides that the particle characteristics, in particular the particle speed and / or particle acceleration, are determined as a function of the time offset between the first measuring beam and the second measuring beam. It is particularly advantageous that the particle speed and the particle position can be detected simultaneously using the device and / or the method. For this purpose, the device can be set up to detect the particle speed and the particle position. Further advantages, features and details emerge from the following description, in which various embodiments of the invention are shown with reference to the drawing. The features mentioned in the claims and the description can each be essential to the invention individually or in any desired combination.

[0028] It shows :

[0029] Fig. 1 is a schematic view of an inventive

[0030] Device for characterizing a particle;

[0031] Fig. 2 is a sectional view of a light beam with a location-dependent intensity distribution and polarization distributions;

[0032] Fig. 3 shows two diagrams, each with a polarization-dependent intensity distribution, where the rotation order is 1 in each case, the polarization distributions being phase-shifted;

[0033] Fig. 4 shows two diagrams, each with a polarization-dependent intensity distribution, with the rotation order being 1 for the first light beam and 7 for the second light beam;

[0034] Fig. 5 shows two diagrams, each with a polarization-dependent intensity distribution, with the rotation order being 6 for the first light beam and 7 for the second light beam;

[0035] Fig. 6 two diagrams, each with a polarization-dependent intensity distribution, where the rotation order of the first light beam

[0036] 0 and the second light beam 1; and

[0037] Fig. 7 is a sectional view of two parallel light beams with two location-dependent intensity distributions.

[0038] The device 10 for characterizing a particle 12 has, according to Fig. 1, a light source 14, in particular in the form of a laser, and a beam shaping optics 16 with a vortex plate and a cylindrical lens.

[0039] The light source 14 serves to generate an output beam 18 extending parallel to a beam axis 22. The light beam 20 is separated in the beam-shaping optics 16 into two or more light beams 20 extending parallel to the beam axis 22. Alternatively, the light source 14 can independently generate two or more such light beams 20, so that separation in the beam-shaping optics 16 can be dispensed with.

[0040] The light beams 20 serve in sections as a measuring volume 24 . For this purpose, the light beams 20 each form a light curtain 26 through which the particles 12 to be characterized pass. In Fig. 1, a first light curtain 26A and a second light curtain 26B are shown. The particles 12 pass through the light curtains 26 during a relative movement between the particle 12 and the device 10, wherein the movement path of the particle 12 runs obliquely, preferably perpendicularly, to the light curtain 26. It is conceivable that the device 10 and / or the particle 12 moves. According to Fig. 1, the particle 12 is in a position in front of the first

[0041] Light curtain 26A, shown in a position in the first light curtain 26A and a position in the second light curtain 26B. The light source 14 and / or the beam-shaping optics 16 are preferably configured such that the first light curtain 26A and the second light curtain 26B run parallel to one another according to Fig. 7.

[0042] The first light curtain 26A and the second light curtain 26B each have a location-dependent intensity distribution and a location-dependent polarization distribution. Polarization-dependent intensity curves for the first light curtain 26A and for the second light curtain 26B are shown as examples in Figs. 3 to 6.

[0043] The particle 12 located in the measuring volume 24, in particular the particle in the first light curtain 26A and the second light curtain 26B, reflects and / or scatters the respective light beam 20 at least partially in the form of a measuring beam 28. A first measuring beam 28A results from the particle 12 in the first light curtain 26A and a second measuring beam 28B results from the particle 12 in the second light curtain 26B, which are each collected in one or more beam-shaping elements 30 and fed in a targeted manner to one or more detectors 32. The beam-shaping element 30 can be designed as a collector lens or mirror and / or as an interference element, in particular as a dichroic mirror. The detector 32 preferably encloses a small angle with the light source 14 in relation to the measuring volume 24. The detector 32 and the light source 14 are preferably designed to be positionally fixed to one another.

[0044] The measuring beams 28 have a plurality of polarization-dependent intensities, which can be determined by means of the at least one detector 32. An evaluation unit 34, which can be designed separately or integrated into the detector 32, determines the desired particle position within the measuring volume 24 depending on at least one polarization-dependent intensity of the measuring beam 28.

[0045] According to Fig. 1, the particle 12 passes through the first light curtain 26A at time t1, so that the detector 32 detects a first measuring beam 28A at time t2, and through the second light curtain 26B at time t1, so that the detector 32 detects a second measuring 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 the particle 12. The evaluation unit 34 is configured to generate a first intensity signal based on the first measuring beam 28A and a second intensity signal based on the second measuring beam 28B, which in each case represents the position of the particle 12 in the light curtains 26. The use of multiple light curtains 26 already results in improved accuracy in the characterization of the particle 12.This results from the assumption that the particle 12 hits the same position of the light curtains, in particular moves perpendicular to the light curtains 26. Furthermore, the evaluation unit 34 is preferably set up in such a way that it detects the position in the respective light curtain 26A as a function of the measuring beams 28 and determines the direction of movement of the particle 12 from this. Furthermore, the evaluation unit 34 is preferably set up in such a way that it determines the particle speed of the particle 12 as a function of the measuring beams 28 and as a function of the time difference between the detection of the measuring beams 28 (Δt = t4-t2) at a known distance between the light curtains 26. The distance between the light curtains 26 is preferably to be selected in such a way that between the times t1 and t3 only one particle 12 is arranged in the measuring volume 24, in particular between the first light curtain 26A and the second light curtain 26B.The characterization of the particle 12 preferably takes place in real time. The distance is preferably in a range between 50 pm and 10 mm, preferably between 50 pm and 7 mm, preferably between 50 pm and 1 mm.

[0046] According to Fig. 2, the light rays 20 in a first curtain plane 27A, in which the first light curtain 26A is arranged, and / or in a second curtain plane 27B, in which the second light curtain 26B is arranged, essentially have the shape of an oval 36 with two axes of symmetry, i.e. an ellipse. Fig. 2 shows, for example, the polarization distribution of the second light curtain 26B, i.e. the lower diagram, according to Fig. 3. Along a vertical axis H running perpendicular to the beam axis 22, the oval 36 has a height dimension 38 which is greater than a width dimension 40 running along a width axis B, the width axis B running perpendicular to the vertical axis H and perpendicular to the beam axis 22. The vertical axis H preferably runs vertically and the width axis B preferably horizontally.The intensity of the light rays 20 is distributed such that it is maximum in the area center 42 of the oval 36 and decreases continuously towards an outer contour 44 of the oval 36, in particular is minimum in the observed area at the outer contour 44 of the oval 36. Within the oval 36, in a plane that runs perpendicular to the curtain plane 27A, 27B, there is a two-dimensional intensity distribution that preferably corresponds to a Gaussian intensity distribution. In other words, the intensity runs continuously in an area between the area center 42 and the surrounding outer contour 44, with the intensity decreasing from the area center 42 in the radial direction towards the outer contour 44. Other intensity distributions for the light rays 20 are also conceivable, such as a Laplace distribution, a logistic distribution or a Cauchy distribution, wherein the light rays 20 can have the same or different intensity distributions.

[0047] Such an intensity distribution has the effect that the light rays 20 can be reflected along the vertical axis H of the oval 36 with different intensities in the form of the measuring beams 28. By measuring the intensity of the measuring beams 28, a particle characteristic can be determined with high accuracy. If the particle characteristic to be determined is a particle position, it is advantageous to take into account that the intensity of the measuring signal can also vary depending on the particle size. Therefore, the embodiment of the intensity distribution shown in Fig. 2 provides that the beam shaping optics 16 generates a location-dependent polarization distribution with a rotation order N=1, which is indicated in Fig. 2 by the arrows 46, 48, 50, 52, 54.Here, a first polarization 46 and a second polarization 48 are present along the vertical axis H, which are spaced from one another along the vertical axis H of the oval 36 and whose polarization directions are at an angle of 180 degrees to one another. In the region of the surface center 42, a third polarization 50 is present, the polarization direction of which has a polarization angle of 90 degrees to the polarization directions of the first polarization 46 and the second polarization 48. Between the first polarization 46 and the third polarization 50, there is a fourth polarization 52, the polarization direction of which is at an angle of 45 degrees to the polarization direction of the third polarization 50. Between the second polarization 48 and the third polarization 50, there is a fifth polarization 54, which also has an angular difference of 45 degrees to the third polarization 50.Contrary to the representation shown, the location-dependent polarization distribution runs continuously along the vertical axis H and includes the discretely shown polarizations .

[0048] If the particle 12 is located in the projection plane of the respective light curtain 26 and in the region of the vertical axis H of the oval 36, the respective light beam 20 is reflected such that the measuring beam 28 has a plurality of intensity components of different polarization. Taking these polarization-dependent intensity components into account enables the determination of a unique position of the particle 12 within the light curtain 26 or the projection plane.

[0049] 2. The polarization directions of the polarizations 46, 48 are at an angle of 180 degrees, so that a polarization filter is transparent to light with both polarizations 46, 48. The second intensity profile 58 corresponds to the location-dependent intensity of the light beam 20 with the third polarization 50 according to FIG. 2 .The third intensity curve 60 corresponds to the location-dependent intensity of the light beam 20 with the fourth polarization 52 according to Fig. 2. The fourth intensity curve 62 corresponds to the location-dependent intensity of the light beam 20 with the fifth polarization 54 according to Fig. 2. From Fig. 3 it can be seen that the intensity distribution of the two light beams 20 is identical and the polarization distribution of the two light beams 20 is different. The intensity curves 56 and 58 are symmetrical in the second light beam 20. The intensity curves 60 and 62 are asymmetrical in the second light beam 20 and the intensity curves 56, 58 and 60 and 62 are asymmetrical in the first light beam 20.

[0050] If a particle 12 is located in the projection plane of the light beam 20, which corresponds to the image plane of Fig. 2, the reflected measuring beam 28 has a plurality of polarization-dependent intensities which, depending on the y-position of the particle 12, correspond to the intensity profiles 56, 58, 60, 62 according to Fig. 3. If the particle 12 is therefore located, for example, at a height of 0 pm along the y-axis, the measuring beam 28 has a dominant intensity component which corresponds to the first intensity profile 56 and has the corresponding first polarization 46. At the same time, the measuring beam 28 in this example has less pronounced intensity components which correspond to the third intensity profile 60 and the fourth intensity profile 62 and the corresponding fourth polarization 52 and 54 respectively. fifth polarization 54 .In other words, at the y-position of 0 pm, the first polarization 46 according to Fig . 2 predominates, which can, however, be represented by linear superposition of equal parts of the second polarization 48 and the third polarization 50 according to Fig . 2 .

[0051] By measuring the polarization-dependent intensities using detector 32, these can be assigned to a unique position of particle 12 along the y-axis, for example, using a mathematical model or a table. The asymmetrical course of the intensity curves allows, in particular, a clear distinction between two particle positions along the y-axis.

[0052] The detector 32 is designed to determine the direction of polarization. In the exemplary embodiment of the device 10 shown in Fig. 1, a measuring beam is split into two beams in a beam-shaping element 30, in the form of a so-called 50:50 beam splitter, independently of polarization. Along one optical path, behind this beam splitter, there is a polarization beam splitter and in each output path there is a photodiode (photodiodes 1 and 2). Along the other path there is a polarization-rotating element for polarization rotation by 45° (for example a lambda / 2 plate), followed by a polarization beam splitter and in each output path there is a photodiode (photodiodes 3 and 4). The photodiodes are designed to detect different polarization components. A first photodiode 1 is designed to have 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. The photodiodes 3 and 4 are designed to detect the fourth polarization 52 and the fifth polarization 54 according to Fig. 2. Upon detection of the split measuring beam 28, the photodiodes each output an electrical signal which corresponds to the intensity of the correspondingly measured light component of one of the aforementioned polarizations. The signals are evaluated in the evaluation unit 34, for example using the mathematical model mentioned above. In the embodiment of the device 10 shown in Fig. 1, a measuring beam is split into two beams in a beam-shaping element 30, in the form of a so-called 50:50 beam splitter, independent of polarization. Two photodiodes designed to detect different polarization components are arranged along the optical path behind this beam splitter.A 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 is designed to detect the fourth polarization 52 and the fifth polarization 54 according to Fig. 2. Upon detection of the split measuring beam 28, the photodiodes each output an electrical signal which corresponds to the intensity of the correspondingly measured light component of one of the aforementioned polarizations. The signals are evaluated in the evaluation unit 34, for example using the mathematical model mentioned above. Fig. 4 shows an alternative intensity and polarization distribution for the light beams 20. The first light beam 20 has a symmetrical intensity and polarization distribution like the second light beam 20 according to Fig. 3.The second light beam 20 has an intensity and polarization distribution with a rotation order of N=7. The first light beam 20 has a rotation order of N=1.

[0053] The "rotation order" represents a measure for a light beam 20 which describes the spatial variation of the polarization plane or polarization direction. The rotation order quantifies the frequency with which the polarization direction of a light beam 20 along the height axis completes a full 180° rotation from an orientation along the x-axis to an orientation opposite to the x-axis, such as from horizontally left according to the first polarization 46 to horizontally right according to the second polarization 48. With a polarization order of 0, the polarization plane or polarization direction is constantly oriented in one orientation, as is shown for the first light beam 20 in Fig. 6. With a polarization order of 1, the polarization plane or polarization direction rotates. the polarization direction by 180 ° along the height extension of the light beam 20 once , as it is for both light beams 20 in Fig .3 and for the first light beam 20 in Fig. 4 and 6. With a polarization order of greater than 1, the polarization plane or the polarization direction rotates by 180° along the vertical extent of the light beam several times, as is shown for the second light beams 20 in Fig. 4 and 5 and for the first light beam 20 in Fig. 5. It is of course conceivable that incomplete rotations of the polarization plane by 180° occur. In this case, the laws of mathematics allow rounding up or down to the nearest whole number. For example, a light beam 20 with a rotation of the polarization plane of 390° then has a rotation order of 2 (rounded down from 390° / 180° = 2.17). Alternatively, the rotation order can be rounded to 0.5 or 0.1 steps.

[0054] A larger rotation order means that a particle's displacement along a polarization variation axis results in a larger change in polarization direction. The variation axis runs along the vertical axis H. Therefore, the angle of polarization can be used to determine the particle's position in the projection plane with greater accuracy. In other words, a larger rotation order N results in greater resolution.

[0055] As already described in Fig. 3, a rotation order greater than 1 causes a rotation direction (e.g. horizontal) to occur multiple times along the height axis H of the light beam 20. Thus, based on the one measurement signal of one measurement beam, no reliable statement can be made, for example, about the position of the particle 12. With a measurement beam 28, the measured polarization would allow conclusions to be drawn about several positions in the second light curtain 26B. In this case, the polarization distribution in the first light curtain 26A is set such that different polarization directions are present at these positions. Thus, the exact position of the particle 12 can be concluded from the combination of the first measurement signal and the second measurement signal. Due to the higher rotation order of the first and / or second light beam 20, a higher measurement accuracy results overall, without the measurement volume or the

[0056] Light curtain 26 to reduce or increase.

[0057] According to Fig. 5, the first light beam 20 has a rotation order of N=6 and the second light beam 20 has a rotation order of N=7, which corresponds to a Vernier scale ("Nonius"). Accordingly, a further increase in measurement accuracy is possible. According to Fig. 6, the first light beam 20 has a rotation order of N=0 and the second light beam 20 has a rotation order of N=1. In Fig. 3, the first light beam 20 and the second light beam 20 have a rotation order of N=1. In addition to or alternatively to the rotation order, the first and second light beams 20 can also differ in terms of the intensity distribution or in terms of a phase shift, as in Fig. 3.

[0058] The light source 14 can further be designed to project two light beams 20 with different wavelengths X2, X2 along a respective beam axis 22, which possibly overlap in the projection plane and thereby have the location-dependent intensity distribution and a location-dependent wavelength distribution and in particular a location-dependent polarization distribution, and wherein the detector 32 is designed to detect at least one wavelength-dependent intensity of the measuring beam 28 and to output a wavelength-dependent intensity signal to the evaluation unit 34, wherein the evaluation unit 34 is designed to determine a particle position within the measuring volume 24 depending on the wavelength-dependent intensity signal. With the location-dependent wavelength distribution, in addition to the

[0059] Intensity of the measuring beam 28, a further light property must be taken into account in order to be able to clearly determine a particle characteristic. The location-dependent wavelength distribution can in particular be used in addition to or alternatively to a location-dependent polarization distribution in order to be able to clearly determine a particle position within the measuring volume 24. A light beam 20 with an intensity distribution and a wavelength distribution means that the light beam 20 reflected or scattered by the particle 12 in the form of the measuring beam 28 can have at least two wavelength components, the consideration of which enables a clear determination of the position of the particle 12 within the projection plane. Here, too, a second light curtain 26B brings about greater accuracy in the position determination.

[0060] The detector 32 can have a plurality of photodiodes that are wavelength-sensitive, or a plurality of wavelength-dependent beam splitters, so that a detected reflection beam with different wavelength components leads to different signal amplitudes of the corresponding photodiodes. The evaluation of the wavelength-dependent signals can be carried out using a mathematical model, a table or a characteristic curve in order to be able to determine the particle characteristics, in particular the particle position. The beam-shaping element 30 can in this case have an interference element, in particular a dichroic mirror, so that the measurement signals can be guided to different detectors 32 based on the different wavelengths. It is also conceivable for the two light curtains 26A, 26B to differ based on different wavelengths Xi, X2.

[0061] When using different wavelengths, the separation of the light rays 20 can alternatively be carried out using refractive / diffractive methods, such as prisms or diffractive gratings.

[0062] It may be advantageous to use flat-top beams for the light beams 20, since these do not exhibit a decreasing signal-to-noise ratio toward the end of the light curtain 26. The flat-top beams can be used for all of the aforementioned embodiments.

[0063] List of reference symbols

[0064] B Width measurement

[0065] H height dimension

[0066] N rotation order

[0067] 10 Device

[0068] 12 particles

[0069] 14 Light source

[0070] 16 Beam shaping optics

[0071] 18 Output beam

[0072] 20 light beam

[0073] 22 Ray axis

[0074] 24 measuring volumes

[0075] 26 light curtain

[0076] 26A first light curtain

[0077] 26B second light curtain

[0078] 27A first curtain level

[0079] 27B second curtain level

[0080] 28 measuring beam

[0081] 28A first measuring beam

[0082] 28B second measuring beam

[0083] 30 beam shaping element

[0084] 32 detector

[0085] 34 Evaluation unit

[0086] 36 Oval

[0087] 38 Height dimensions

[0088] 40 width dimensions

[0089] 42 Center of area

[0090] 44 Outer contour

[0091] 46 first polarization

[0092] 48 second polarization

[0093] 50 third polarization

[0094] 52 fourth polarization

[0095] 54 fifth polarization

[0096] 56 first intensity curve

[0097] 58 second intensity curve

[0098] 60 third intensity curve

[0099] 62 fourth intensity curve

Claims

Patent claims 1. Device (10) for characterizing a particle (12), comprising: at least one light source (14) for projecting at least one first light beam (20) running parallel to a beam axis (22) and at least one second light beam (20) running parallel to the beam axis (22), wherein the at least one first light beam (20) and the at least one second light beam (20) are arranged at a distance from one another perpendicular to the first beam axis (22), at least one beam shaping optics (16) which is arranged along the beam axis (22) and is designed to generate, in a measuring volume (24) which extends in sections along the beam axis (22), a location-dependent intensity distribution and / or a location-dependent polarization distribution of the first light beam (20) along a first curtain plane (27A) and of the second light beam (20) along a second curtain plane (27B)at least one detector (32) which is designed to detect a first measuring beam (28A) reflected and / or scattered by the first light beam (20) from the particle (12) and a second measuring beam (28B) reflected and / or scattered by the second light beam (20) from the particle (12) and to output at least one measuring signal to an evaluation unit (34), the evaluation unit (34), which is designed to determine a particle characteristic as a function of the first measuring beam (28A) and the second measuring beam (28B); wherein the beam-shaping optics (16) are designed to form the location-dependent intensity distribution and / or the location-dependent polarization distribution in the first curtain plane (27A) and / or the second curtain plane (27B) in such a way that an intensity of the first and / or second light beam (20) is minimal along an outer contour (44) of an oval (36) and is maximal at at least one point within the oval (36), and / or that at least one first polarization (46) and one second polarization (48) with different polarization directions are present along a vertical axis of the oval (36) of the first and / or second light beam (20);wherein the intensity distribution of the first light beam (20) along the first curtain plane (27A) and the second light beam (20) along the second curtain plane (27B) differ, and / or wherein the polarization distribution of the first light beam (20) along the first curtain plane (27A) and the second light beam (20) along the second curtain plane (27B) differ.; 2. Device (10) according to claim 1, wherein the light source (14) and / or the beam shaping optics (16) are designed such that the first light beam (20) and the second light beam (20) run parallel to each other and / or that the first curtain plane (27A) and the second curtain plane (27B) run parallel to each other.

3. Device (10) according to claim 1 or 2, wherein the light source (14) and / or the beam-shaping optics (16) are designed such that the first light beam (20) has a polarization distribution with a first rotation order and the second light 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. Device (10) according to 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 differ.

5. Device (10) according to claim 3 or 4, 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. Device (10) according to claim 3 to 5, 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 each a different prime number.

7. Device (10) according to one of claims 3 to 6, 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 differ by 1.

8. Device (10) according to one of claims 3 to 7, 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 0.

9. Device (10) according to one of the preceding claims, wherein the light source (14) and / or the beam-shaping optics (16) are designed such that the polarization distribution of the first light beam (20) and the second light beam (20) differ with regard to a phase shift of the polarization.

10. Device (10) according to one of the preceding claims, wherein the beam shaping optics (16) have a shaping element, wherein the shaping element is configured to generate an at least partially linear or non-linear polarization pattern and / or wherein the shaping element is designed as a wave plate, in particular a vortex plate or S-wave plate, and wherein in particular the light source (14) and / or the beam shaping optics (16) are designed such that the first light beam (20) and the second light beam (20) are projected onto two different radial positions of the shaping element.

11. Device (10) according to one of the preceding claims, wherein the light source (14) and / or the beam-shaping optics (16) are designed such that the first light beam (20) and the second light beam (20) differ in wavelength, wherein along the first measuring beam (28A) and / or the second measuring beam (28B) a Interference element, in particular a dichroic mirror, is provided for separating the first measuring beam (28A) and the second measuring beam (28B).

12. Device (10) according to one of the preceding claims, wherein the beam shaping optics (16) comprises a birefringent element and / or a biprism for generating at least two light beams (20) running parallel to one another.

13. Device according to one of the preceding claims, wherein the evaluation unit (34) is further configured to determine a particle characteristic depending on a polarization direction of the first measuring beam (28A) and the second measuring beam (28B).

14. A method for characterizing a particle (12), comprising the following steps: a) projecting a first light beam (20) and a second light beam (20) parallel to a beam axis (22), wherein in a measuring volume (24), the first light beam (20) along a first curtain plane (27A) and the second light beam (20) along a second curtain plane (27B) have a location-dependent intensity distribution and / or a location-dependent polarization distribution; b) reflecting and / or scattering the first light beam (20) from the particle (12) as a first measuring beam (28A) and the second light beam (20) from the particle (12) as a second measuring beam (28B); c) determining a particle characteristic of the particle (12) within the measuring volume (24) as a function of of the first measuring beam (28A) and the second measuring beam (28B), wherein the intensity distribution of the first light beam (20) along the first curtain plane (27A) and of the second light beam (20) along the second Curtain plane (27B) and / or wherein the polarization distribution of the first light beam (20) along the first curtain plane (27A) and the second light beam (20) along the second curtain plane (27B) differ.

15. The method according to the preceding claim, wherein the particle characteristic is determined as a function of a polarization direction of the first measuring beam (28A) and / or the second measuring beam (28B).

16. The method according to claim 14 or 15, wherein the Particle characteristics are determined as a function of the time offset of the first measuring beam (28A) and the second measuring beam (28B).

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