Determination of grating vectors of volume holographic gratings

Abstract

The invention relates to a method for determining a grating descriptor of a hologram, the method comprising the following steps: a) illuminating a first region of the hologram with a light source from at least three directions of incidence, b) detecting light transmitted through the hologram for each of the at least three directions of incidence, and c) determining a grating descriptor for the first region at least partially on the basis of the detected transmitted light and the associated direction of incidence.

Description

[0001] 29- August 2025 Carl Zeiss Jena GmbH Z17O784WO ANE / Ris / Mak

[0002] DETERMINATION OF THE GRID VECTORS OF VOLUME HOLOGRAPHIC GRIDS

[0003] 1. Technical field

[0004] The invention relates to methods, devices and computer programs for determining a lattice descriptor of a hologram.

[0005] 2. State of the art

[0006] Numerous methods for characterizing holograms or volume holographic lattices have been published and some are even standardized in norms. However, none of these describe a universal method for determining lattice descriptors, such as lattice vectors, from the measured values.

[0007] For example, P. Vojtisek, M. Kveton, and I. Richter, “Complex method for angular-spectral analysis of volume phase diffraction gratings recorded in photopolymers.” J. Eur. Opt. Soc 11 (2016): 16009, refers to angular spectral measurements for the characterization of diffraction volume phase gratings. Specifically, a sample to be characterized is oriented on a rotating platform at an angle of 90° to a measurement beam. By incrementally rotating the sample relative to the measurement beam by 180°, the transmitted spectrum is acquired and analyzed stepwise (e.g., in 0.025° steps). After a complete rotation, the spectral information is compiled into an angular spectral dataset. The quasi-continuous measurement of the sample over an angular range of 180° results in high time, cost, and computational costs for the analysis of the resulting angular spectral data.

[0008] The international standard for measuring the diffraction efficiency and associated optical properties of holograms, ISO 17901-1, describes methods for measuring holograms using two detectors. Specifically, the radiation flux of an incident wave is measured with the first detector, and the radiation flux of the reconstructed wave is measured with the second detector.

[0009] This means that the corresponding measurements in both methods can only be performed if the second detector is correctly positioned, covering a position to which the light from the respective hologram is deflected. This can be technically and time-consuming. Especially with holograms to be characterized, this position cannot be predicted without difficulty, which can lead to complications in the procedure and / or necessitate the use of very large detectors.

[0010] The present invention is therefore based on the objective of providing improved solutions for the characterization of holograms or volume holographic grids.

[0011] 3. Summary of the invention

[0012] This task is at least partially solved by the aspects described herein.

[0013] One aspect of the invention relates to a method for determining a grating descriptor of a hologram. The method comprises steps a) to c), namely: a) illuminating a first region of the hologram with a light source from at least three directions of incidence, b) detecting light transmitted by the hologram (e.g., the illumination) for each of the at least three directions of incidence, and c) determining a grating descriptor for the first region, at least partially, based on the detected transmitted light and the respective corresponding direction of incidence. The determination of the grating descriptor of the hologram can, for example, include identifying and / or measuring an (existing) grating descriptor of the hologram.

[0014] The present invention is based, among other things, on the understanding that diffraction in (volume-phase diffraction) gratings, e.g., holograms, is a consequence of periodic spatial refractive index modulation. The spatially varying value of the refractive index n(r) can be approximated as follows: where n0 is the mean refractive index, where is the amplitude of the first refractive index modulation order, K is the reciprocal lattice vector, and r is the position vector. The values ​​of zi; for i > 1 represent amplitudes of higher refractive index modulation orders.

[0015] The Bragg condition in periodic lattices with a distance d between adjacent lattice planes

[0016] 2d sin(0) = mA with 77i e Ho, the angle 9 between the grating plane and the incident or emerging light, and the wavelength A is well known. From the definition of the wave vector

[0017] 2n k =and the (one-dimensional) reciprocal lattice vector

[0018] 2nm

[0019] K = ~cT follows:

[0020] K = 2k sin(0).

[0021] It can be directly deduced from this that for 9 = 90° (i.e., for wave vectors perpendicular to the lattice planes):

[0022] K = 2k.

[0023] This case corresponds to perpendicular reflection at the lattice planes. This representation is consistent with the equally well-known Laue condition.

[0024] K = k d - k t for k t = —k d , where momentum is conserved \k d \ = \k tHowever, this relationship cannot be utilized in conventional methods and devices, since the light can only be applied to the grating to be measured at a precise angle to the grating plane once the grating plane orientation is fully known. In this case, the grating would already be completely measured. Furthermore, the necessary accuracy with which the light would have to be applied to the sample to be measured is difficult to achieve, or only achievable with considerable effort and / or expense, due to mechanical factors, for example.

[0025] According to one aspect of the present invention, this relationship can nevertheless be exploited to measure samples. Specifically, measuring the sample from at least three directions of incidence makes it possible to determine a grating descriptor, e.g., by exploiting the Laue condition, without using the detector to detect the light deflected by the hologram, which is also referred to as the first diffraction order. Instead, the grating descriptor can be determined based on the light transmitted by the hologram, which is also referred to as the zeroth diffraction order, e.g., in a straight-line arrangement of the light source and detector. In transmission, the detector can be placed essentially opposite the light source in a simple, efficient, and inexpensive manner, which can accelerate and / or simplify the method and the equipment involved.Put simply, instead of a "peak" in the light deflected by the hologram or the first diffraction order, a "dip" in the light transmitted by the hologram or the zeroth diffraction order can be determined to find the grating descriptor.

[0026] Optional embodiments of steps a), b) and c) are described herein:

[0027] Step a) can be performed, for example, as follows:

[0028] In one example, illumination might involve polychromatic illumination of the first region of the hologram, e.g., for each of the at least three directions of incidence. Similarly, in some examples, detection of the light transmitted by the hologram, e.g., for each of the at least three directions of incidence, might also involve polychromatic detection.

[0029] This approach allows for the simultaneous examination of multiple wavelengths, and preferably a broad spectrum of wavelengths, making it possible to measure many different holograms even if their exposure wavelengths are not known beforehand. This can expand the application range of the method.

[0030] Polychromatic illumination can encompass a spectrum with multiple wavelengths. The light for polychromatic illumination can be provided by various light sources, including, but not limited to, the following examples: Optionally, the light source can include a broadband light source module, such as a tungsten-halogen lamp, a supercontinuum laser, laser-pumped plasma light sources, or a light-emitting diode (LED) array capable of emitting a spectrum spanning multiple wavelengths. The light source can, for example, include one or more wavelength-tunable lasers, such as dye lasers and / or semiconductor lasers, e.g., with diode elements (with individually adjustable activation and / or intensity), which can, for example, enable selective emission at different wavelengths within a predefined wavelength range.The light source can, for example, comprise a filter wheel assembly, where a filter wheel can selectively transmit specific wavelength bands from a light source. This allows, for instance, the sample to be illuminated sequentially or simultaneously with several (different) wavelengths. The light source can, for example, combine one or more of these and / or other examples, e.g., to combine multiple wavelengths for polychromatic illumination, for instance, using fiber couplers or partially reflective mirror arrangements.

[0031] In one example, the polychromatic illumination can include a first wavelength and a second wavelength, the first wavelength being 100 nm or more, preferably 500 nm or more, different from the second wavelength. This ensures that a sufficient spectral wavelength range is covered to detect the light transmitted by the hologram. Further spectral coverage, or detection at a multitude of wavelengths, can thus increase the accuracy and reliability of the method. In general, increased spectral coverage and / or resolution can lead to a more precise determination of the grating descriptor.

[0032] In principle, continuous and / or discontinuous spectra can be provided. The respective spectra of the polychromatic illumination can be provided by one or more light sources. For example, several illuminations with essentially monochromatic light with a finite linewidth and / or with polychromatic or broadband light can be spatially superimposed. The illuminations of the spatially superimposed light sources can at least partially overlap spectrally or be disjoint.

[0033] A continuous spectrum, which includes, for example, the first and second wavelengths, can be characterized by the fact that the first and second wavelengths lie within the continuum and / or the light intensities at the first and second wavelengths are more than 10%, preferably more than 50%, of the maximum light intensity of the continuous spectrum. Preferably, the first and second wavelengths can represent the start and end wavelengths of the bandwidth of the continuous spectrum, the bandwidth being, for example, defined by the full width at half maximum (FWHM) of the spectrum.

[0034] For example, polychromatic illumination can comprise illumination in a spectral range with a width of at least 100 nm, preferably 400 nm, and more preferably 700 nm. The width of the spectral range can be determined by the full width at half maximum (FWHM) and / or by the width of the spectral range in which the luminous intensity exceeds 10%, preferably more than 50%, of the luminous intensity maximum, and / or in which an envelope of the luminous intensity peaks exceeds 10%, preferably more than 50%, of the luminous intensity maximum. For example, polychromatic illumination can also comprise sampling with multiple wavelengths (i.e., at least a first and a second wavelength) that are spaced in pairs no more than 10 nm, 5 nm, or 2 nm apart. However, the wavelengths can span a spectrum of, for example, at least 100 nm or more (as described herein).

[0035] In a preferred embodiment, at least two of the at least three directions of incidence define a plane that is at an angle of at least 1°, preferably at least 10°, to at least one further of the at least three directions of incidence. In principle, any two of the at least three directions of incidence can define a plane that is at an angle of at least 1°, preferably at least 10°, to each further of the at least three directions of incidence, such that, for example, no three of the at least three directions of incidence lie in a single plane.

[0036] This can be particularly advantageous in allowing the lattice descriptor to be determined more accurately and / or reliably. Specifically, it can lead to the hologram being illuminated in such a way that, as described in step c), the vectors determined for each direction of incidence do not lie on a straight line but are instead sufficiently far apart. This allows, for example, as described in step c), a fit plane to be determined with increased accuracy. A fit plane (also called a fitting plane, for example) can be, as explained in more detail below, a plane containing the endpoints of the determined vectors, and / or a plane that minimizes the sum of the squared distances of the vector endpoints from the plane.

[0037] In a preferred embodiment, the at least three directions of incidence lie on a predetermined conical surface. This allows for particularly efficient guidance of the light source, which can also ensure that the directions of incidence do not lie in a plane, as advantageously described herein. The spatial distribution of the directions of incidence thus achieved can improve the accuracy and reliability of the method. Step b) can, for example, be performed at least partially based on step a) and / or at least partially simultaneously with step a). Specifically, in a preferred embodiment, the detection of step b) can take place at least partially when the illumination according to step a) occurs.

[0038] Step b) can be carried out, for example, as follows:

[0039] For example, the light transmitted by the hologram can essentially be detected along the respective direction of incidence.

[0040] This offers the advantage that the detector can always be positioned essentially opposite the light source. This detector placement can be achieved regardless of how the hologram deflects light (which, given the measurements taken, may not yet be known). This simplifies the process and saves material, costs, and labor.

[0041] Computational effort.

[0042] In principle, the transmission behavior of a hologram can be based on a hologram-specific spectral diffraction effect. For example, the spectral diffraction effect can include the deflection of light by the hologram. Detecting the light transmitted by the hologram can involve measuring a transmission spectrum. Likewise, it can include detecting measurements related to the transmission spectrum, such as measuring absorption, diffuse scattering, diffraction efficiency, and / or reflection, or converting these measurements.

[0043] Furthermore, the method can include alternative ways of detecting the spectral diffraction effect, where the spectral diffraction effect can encompass a relationship between an optical response of the hologram and a spectral measure. The optical response can include, for example, light intensity, light deflection, absorption, reflection, scattering, transmission, and / or the direction of emission of the deflected light or illumination. The spectral measure can include, for example, a wavelength, energy, frequency, wavenumber, wave vector, and / or the direction of incidence of the illumination.

[0044] In principle, quantities used here to characterize light and / or gratings are to be understood as also encompassing those quantities into which they can be converted (with or without consideration of material parameters). For example, the wavelength can be converted into the wave vector.

[0045] In one example, the method can further include determining at least one local and / or global spectral transmission minimum along the respective direction of incidence.

[0046] The method can, for example, also include a correction of the direction (or angle) of incidence of the illumination, at least partially based on a refraction effect.

[0047] For example, the refraction effect can include refraction at a surface of the hologram.

[0048] This is based on the inventors' understanding that, upon striking the surface of the hologram, the illumination is refracted due to the refractive index differences between the refractive index of the hologram (UH) and that of the medium (UM) surrounding the hologram, e.g., air, an atmosphere controlled in pressure and / or composition, or a vacuum (except in the special case where the illumination strikes the surface of the hologram exactly perpendicularly). Thus, the direction of incidence of the illumination inside the hologram can differ from the direction of incidence of the illumination outside the hologram. The correction of the direction of incidence can be achieved by determining the direction of incidence of the illumination inside the hologram (e.g., expressed by the angle α) based on the direction of incidence of the illumination outside the hologram (e.g., expressed by the angle Cα), e.g.,Based on Snell's law of refraction nH-sin(an) = nM-sin(aM). The determination of the grating descriptor can (regardless of how specifically the correction is carried out) be based, for example, on the corrected direction of incidence, i.e., the direction of incidence of the illumination within the hologram, so that the direction of incidence under which the illumination actually interacts with the hologram is taken into account.

[0049] Similarly, the detector positioning can be adjusted accordingly relative to the light source.

[0050] In step c), the lattice descriptor can be determined, for example, as follows:

[0051] For example, the at least one lattice descriptor may include a reciprocal lattice vector, a representation of the reciprocal lattice vector, at least one vector of the transmitted light and / or a plane of adjustment (e.g. as described herein).

[0052] The reciprocal lattice vector K, or another representation thereof, has proven to be a suitable descriptor, which, in the context of the Laue condition K = k described herein, d — k t suitable for describing and / or characterizing the hologram in its interaction with light.

[0053] The lattice descriptor determined in step c), e.g., the representation of the reciprocal lattice vector mentioned herein, can comprise at least one of the following lattice descriptors: a lattice vector, a lattice constant, a plane of regression, and one or more wave vectors (e.g., hologram- and / or illumination-specific). These exemplary lattice descriptors can at least partially describe or characterize the hologram (lattice).

[0054] The lattice descriptor can, for example, be a function of location / position, i.e., in the hologram plane of the hologram expressed by the coordinates (x,y), a function of the x and y values ​​of the respective position. For example, a first coordinate (xi,yi) can define the first area of ​​the hologram and a second coordinate (x2,y2) can define the second area of ​​the hologram, where the first and second coordinates can be different and / or the first area can be different from the second area.

[0055] In one example, determining (e.g., ascertaining) the at least one

[0056] Lattice descriptors comprise determining (e.g., identifying) at least one vector per direction of incidence, wherein preferably the direction of incidence can determine the direction of the vector, and / or wherein preferably the light transmitted through the hologram can determine the magnitude of the vector.

[0057] Determining (e.g., ascertaining) the vector can represent a simple, efficient, and reliable determination of a lattice descriptor, whereby at least the vectors from the at least three directions of incidence can already represent a lattice descriptor.

[0058] The at least one vector determined in this way can be understood as having its starting point at the origin (0) and its endpoint thus defining a point in the corresponding coordinate system. Specifically, determining the at least one vector for each direction of incidence can proceed as follows:

[0059] First, the direction of incidence, the direction of the vector, can be determined, for example, as follows: The direction of incidence can be determined by defining the orientation of the light source relative to the hologram, its surface, and / or a hologram support. One or more of these values ​​can be, for example, control parameters received by an automatic positioning unit of the light source to position the light source accordingly. For example, a coordinate system can be defined where the x and y axes lie in the plane of the hologram and the z-axis is perpendicular to the hologram surface. The x, y, and z coordinates of the vector e can then be determined, for example, by the polar angle 0 and the azimuthal angle cp as follows: e = A - (sin(0) - cos(cp), sin(0) - sin(cp), cos(0)). Here, the polar angle 0 defines the angle between the direction of incidence and the z-axis, and the azimuthal angle cp defines the rotation angle about the z-axis.Instead of this spherical coordinate representation, other forms of representation can also be chosen. The magnitude A of the vector e is not yet determined in this example.

[0060] The magnitude A of the vector can be determined based on the light transmitted by the hologram, for example, as follows: In a preferred embodiment, determining the at least one grating descriptor can be based at least partially on the transmission minimum along the respective direction of incidence. Specifically, the light transmitted by the hologram can include one or more local transmission minima. Each transmission minimum can have a central wavelength Xmin, determined, for example, by fitting. From the central wavelength, a corresponding Wave vector magnitude k m in = 271 / Xmin. A can then be calculated as A = k mThe value in the polar angle can be determined as 271 / Xmin. This results in the vector e = 271 / Xmin - (sin(0)-cos((p), sin(0)-sin(cp), cos(0)). Thus, in this example, the magnitude of the vector is determined by the wavelength at which the hologram deflects light most efficiently (in the corresponding direction of incidence). In this representation, the transition between the optical media of the sample and the surrounding medium is influenced by refraction effects at a polar angle of 0, as described in step b).

[0061] Determining at least one lattice descriptor can, for example, involve determining (e.g., ascertaining or calculating) a plane of regression. It is expected that the endpoints of the vectors described herein, determined for each direction of incidence and emanating from the origin, span a plane. More precisely, it is expected that this plane is perpendicular to half the reciprocal wave vector K / 2 emanating from the origin. This is because this plane describes the endpoints of all wave vectors emanating from the origin for which the Laue condition can, in principle, be satisfied. Only for vectors k d , which, starting from the origin, land in this plane, can be a vector — k t exist, which under the assumption of conservation of momentum (|k d | = |k t |) leads to K (i.e., starting from the origin exactly to the corresponding point on the opposite side of the plane). This is precisely the Laue condition k. d - k t = K.

[0062] Determining the regression plane can offer the advantage that, for example, several vectors, as described herein, can be considered, averaged, and based on this, a regression plane can be determined as a statistical outlier against robust and reliable grid descriptor.

[0063] Determining the plane of best fit can be done, for example, as follows: If three directions of incidence are taken into account and three vectors are determined based on them, e.g., as described here, then these three vectors determine e t , e2 and e3 uniquely define a plane. This plane can represent the regression plane. The plane can then be mathematically defined by the set of points E = e t + u(e2- <?i) + v(e3- <?i) bestimmt werden, wobei die Vorfaktoren u und v aus den rationalen Zahlen sein können. Sind mehr als drei Vektoren berücksichtigt, kann die Ausgleichsebene z.B. durch Fitting an die vier oder mehr Vektoren ei bestimmt werden.

[0064] To fit a plane to four or more points, this simple and direct method of determination is only applicable to a limited extent. Therefore, in other examples, determining the plane of fit may involve fitting the plane, preferably fitting it to the at least three vectors or the endpoints of the at least three vectors starting at the origin.

[0065] For example, a method can be used that minimizes the least squares (error) values. The goal is to find the plane (e.g., in the form of a plane equation) whose total distance to the given points is the smallest; this corresponds, for example, to the regression plane described herein.

[0066] The adjustment plane described herein can therefore also represent a lattice descriptor that can be determined very reliably and reproducibly, for example by taking into account a large number of vectors (as described herein).

[0067] In one example, determining at least one lattice descriptor may involve determining a perpendicular foot vector to the regression plane.

[0068] This can provide a simple, reliable and meaningful representation of the compensation level, e.g. as described herein.

[0069] For example, the foot vector of the perpendicular from the origin 0 to the regression plane can be determined. This can be done using various known mathematical methods. In one example, the first step involves determining the normal vector n of the regression plane. In a second step, an auxiliary line h = 0 + tn (with the coefficient t) can be determined. In a third step, the point of intersection (the so-called foot F) of the auxiliary line with the regression plane can be determined. In a fourth step, the foot vector OF of the perpendicular can be determined; in the example of 0 = (0,0,0), this could simply correspond to the vector F.

[0070] In one example, determining at least one lattice descriptor may involve doubling the perpendicular foot point vector.

[0071] In the example above, this can then determine the vector K = 2F. The vector K can represent the reciprocal lattice vector of the hologram or the associated lattice. Mathematically, the doubling can be understood using the well-known Laue condition K = k, described here. d — k t For light incident perpendicularly (i.e., along the vector F or 0F), the following applies, for example: k t = —k d , where momentum is conserved |k d | = \k t and the light is reflected back at the grating planes. Therefore, K = 2k d , where k d corresponds to the vector F from the example described above.

[0072] This mathematical doubling of the perpendicular foot vector thus provides a reliable way to determine the lattice descriptor in the form of the reciprocal lattice vector with minimal computational effort.

[0073] The steps of the process described herein can be performed sequentially, at least partially overlapping in time, and / or repeated once. In preferred exemplary embodiments, this can be done as follows:

[0074] In one example, the procedure may involve performing steps ac) for at least a second area of ​​the hologram.

[0075] This allows the method to determine a first lattice descriptor for the first region and a second lattice descriptor for the second region. This enables the spatially resolved determination of the lattice descriptor, allowing for a characterization of the hologram across the region of interest.

[0076] For example, the first, second, and / or subsequent areas can have a size determined by the beam cross-section of the illumination. For example, the area can be approximately circular, e.g., with a diameter of less than 1 mm, preferably less than 0.5 mm.

[0077] The method can, for example, further comprise repeatedly moving the hologram relative to the light source between the first and second regions of the hologram for at least three directions of incidence. The direction of incidence during the movement can preferably be constant and / or the direction of incidence can preferably be changed between repeated movements.

[0078] This can enable the process to be carried out as efficiently and quickly as possible.

[0079] The direction of incidence during movement can, for example, remain constant. This can include methods where the light source is aligned or oriented according to a first direction of incidence and then moved relative to the hologram in this alignment or orientation, and / or the hologram is moved relative to the light source, for example, using a moving stage. This movement illuminates at least the first and second areas in the first direction of incidence. The direction of incidence can then be changed, and at least the first and second areas can be illuminated again, this time in the second direction of incidence. For example, the hologram can be scanned for each direction of incidence. This represents a particularly efficient method that can minimize the number of mechanical adjustments.

[0080] The direction of incidence can be changed over time between repeated movements. This includes examples where the first area is illuminated first from the first and then from the second direction of incidence (and optionally from further directions of incidence), preferably in all directions of incidence provided for the method. Subsequently, the light source and / or the hologram can be moved so that the second area is illuminated first from the first and then from the second direction of incidence (and optionally from further directions of incidence), preferably in all directions of incidence provided for the method. In this way, each area can be completely measured step by step. In one example, the first, second, and preferably at least one further area can be arranged in a regular and / or periodic grid relative to the hologram.

[0081] For example, the period of the regular and / or periodic grid can essentially correspond to the size of the beam cross-section of the illumination, e.g. in the range of 0.5 to 2 times the size of the beam cross-section.

[0082] In principle, the method described herein can be applied to all types of holograms, i.e. not only monochromatic holograms, but also multicolored ones, e.g. RGB holograms.

[0083] In one example, determining at least one lattice descriptor may involve determining a multitude of lattice descriptors for a multitude of lattices.

[0084] The multitude of grids can correspond, for example, to a multitude of colors. For instance, an RGB hologram can be understood as a superposition of three grids, one for each color. This allows for the determination of a multitude of grid descriptors for at least one area, e.g., one for each color.

[0085] A second aspect of the invention relates to a device for determining a grating descriptor of a hologram. The device comprises a light source for illuminating a first region of the hologram from at least three directions of incidence, a detector for detecting light transmitted through the hologram for each of the at least three directions of incidence, and means for automatically positioning and / or orienting the light source and / or the detector along the at least three directions of incidence. Determining the grating descriptor of the hologram can, for example, include identifying and / or measuring an (existing) grating descriptor of the hologram.

[0086] In some embodiments, the detector can include, for example, a CCD and / or CMOS sensor (complementary metal oxide semiconductor), e.g., with an array of individually addressable sensor elements for detecting light, and / or optics (e.g., one or more lenses, mirrors, optical gratings, reflective surfaces, filters, and / or apertures) for directing and / or focusing light or radiation from one or more light sources onto the detector, thus enabling, for example, the analysis of the spectral components of the incident light. The detector can, for example, be positioned essentially opposite the light source. This positioning can be easily accomplished, e.g., automatically and / or by means of a common or coordinated mount for the light source and the detector.

[0087] The device may, for example, include a means for determining the lattice descriptor of the hologram and / or such a means may be coupled to the device (i.e., be set up to receive data from the device and determine the lattice descriptor based on that data).

[0088] In an exemplary embodiment, the light source can include a pivotable mount, and the pivotable mount can be configured to swivel the light source so that at least three directions of incidence lie on a predetermined conical surface. The light source can be guided such that the at least three illuminations light up the same area of ​​the hologram, i.e., the apex of the conical surface lies substantially in the hologram plane. Thus, the direction of incidence can change between the different illuminations (which, for example, lie on a conical surface), but the area remains the same.

[0089] This allows the device to achieve the advantages described herein, which are associated with having at least three directions of incidence on a conical surface.

[0090] In another example, the light source can further comprise an element for influencing the light emitted by the light source, wherein the element for influencing can preferably comprise an autocollimation telescope.

[0091] This can further improve the accuracy and resolution of the device. The inventors have found that, in particular, an autocollimation telescope can be advantageously integrated into the device, leading to especially precisely determined grating descriptors.

[0092] The element for influencing the light emitted by the light source can, for example, be set up to adjust parameters of the lighting such as the spectral composition, intensity, beam cross-section, polarity, etc.

[0093] The device for measuring a hologram can be configured to perform the steps of the procedure as described herein, preferably automatically.

[0094] This can reduce the operating and work effort required to operate the device.

[0095] For example, the device may include a control unit. The execution of the method may be controlled, for example, by means of the control unit (coupled to and / or contained in the device), e.g., a computer, for instance, using a predetermined program. For example, the predetermined program may be selected from a predetermined and / or modifiable list of predetermined programs, wherein the program may include at least one of the parameters described herein.

[0096] Another aspect of the invention relates to a computer program containing instructions which, when the program is executed, cause the device to perform the method for determining the lattice descriptor of the hologram as described herein.

[0097] The computer program can be written in any programming language, including compiled or interpreted languages, and it can be provided in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computer environment. Any functionality described herein with respect to the device can be implemented as a step of the procedure and / or as an instruction of the computer program, and vice versa.

[0098] In some embodiments, the means for performing the steps of the method described herein may include a data processor and / or a storage device. The data processor may control the illumination and / or the detection of the transmitted light. The storage device may store calibration data that correlates the steps and / or the time with a position, direction, illumination, and / or detection parameter. In some implementations, the device may include one or more computers containing one or more data processors configured to execute one or more programs containing a variety of instructions according to the principles described above. Each data processor may contain one or more processor cores, and each processor core may contain logic circuits for processing data.A data processor can, for example, contain an arithmetic and logical unit (ALU), a control unit, and various registers. Every data processor can contain a cache. Every data processor can contain a system-on-a-chip (SoC) that includes multiple processor cores, random-access memory, graphics processing units, one or more controllers, and one or more communication modules. Every data processor can contain millions or billions of transistors.

[0099] The data processing described in this document, such as the determination of the grating descriptor, e.g., based on at least three illuminations and / or the detected transmitted light from at least three directions of incidence, can be performed using one or more computers. These computers may include one or more data processors for processing data, one or more storage devices for storing data, and / or one or more computer programs containing instructions that, when executed by the computer(s), cause the computer(s) to perform the processes. The computer(s) may include one or more input devices, such as a keyboard, mouse, touchpad, and / or speech input module, and one or more output devices, such as a display and / or a speaker.In some embodiments, the one or more computing devices may comprise digital electronic circuits, computer hardware, firmware, software, or any combination of the aforementioned elements. The features relating to data processing may be implemented in a computer program product embodied in an information carrier, such as a machine-readable storage device, for execution by a programmable processor. The process steps may be executed by a programmable processor that executes a program containing instructions for performing functions of the described implementations. Alternatively or additionally, the program instructions may be encoded on a propagated signal, which is an artificially generated signal, such as a signal from a computer.A machine-generated electrical, optical, or electromagnetic signal that is produced to encode information for transmission to a suitable receiving device for execution by a programmable processor.

[0100] The computer(s) can be configured, for example, to run a computer program and may include both general-purpose and specialized microprocessors and one or more processors of any type of digital computer. Generally, a processor receives instructions and data from a read-only memory area, a random-access memory area, or both. The elements of a computer system include one or more processors for executing instructions and one or more memory areas for storing instructions and data. Generally, a computer system also includes, or is operationally coupled to, one or more machine-readable storage media, such as hard disks, magnetic disks, solid-state drives, magneto-optical disks, or optical disks, to receive data from or to them, or both.Machine-readable storage media suitable for embodying computer program instructions and data include various forms of non-volatile memory areas, including, for example, semiconductor memory devices such as EPROM, EEPROM, flash memory devices and solid-state drives; magnetic disks such as internal hard disks or removable media; magneto-optical disks; and CD-ROM, DVD-ROM and / or Blu-ray discs.

[0101] In some implementations, the processes described above can be implemented using software to run on one or more mobile computing devices, one or more local computing devices, and / or one or more remote computing devices (which may be, for example, cloud computing devices). For instance, the software forms procedures in one or more computer programs that run on one or more programmed or programmable computer systems, either in the mobile computing devices, local computing devices, or remote computing systems (which may have different architectures, such as...).distributed, client / server, grid or cloud systems), each comprising at least one processor, at least one data storage system (including volatile and non-volatile memory and / or storage elements), at least one wired or wireless input device or a wired or wireless port, and at least one wired or wireless output device or a wireless port.

[0102] In some embodiments, the software can be provided on a medium such as CD-ROM, DVD-ROM, Blu-ray Disc, a solid-state drive, or a hard disk, which can be read by a general-purpose or specialized programmable computer or delivered (encoded in a transmitted signal) to the computer where it is executed over a network. The functions can be executed on a specialized computer or using specialized hardware, such as coprocessors. The software can be implemented in a distributed manner, with different parts of the computations specified by the software being performed by different computers. Each such computer program is preferably stored on or downloaded to a storage medium or device (e.g., solid-state storage or media, or magnetic or optical media) that...which can be read by a programmable computer for general or special purposes to configure and operate the computer when the storage medium or device is read by the computer system to perform the procedures described herein. The system according to the invention can also be considered a computer-readable storage medium configured with a computer program, wherein the storage medium so configured causes a computer system to operate in a specific and predefined manner to perform the functions described herein.

[0103] The embodiments of the present invention described in this description, and the optional features and properties mentioned in this context, should also be understood as being disclosed in all combinations with one another. In particular, in the present case, the description of a feature belonging to an embodiment—unless expressly stated otherwise—should not be understood as meaning that the feature is essential or indispensable for the function of the embodiment.

[0104] 4. Description of the figures

[0105] Fig. aa shows a schematic representation to explain the Bragg condition.

[0106] Fig. ib shows a schematic representation to explain the Laue condition.

[0107] Fig. ic shows a schematic representation to explain the Laue condition using the Ewald sphere.

[0108] Fig. id shows a schematic representation of the illumination of a hologram in three directions of incidence lying on a conical surface.

[0109] Fig. le shows a schematic representation of the incoming and outgoing directions of the three lighting fixtures from Fig. id as well as a compensation plane and perpendicular foot vector determined on the basis thereof.

[0110] Fig. 15 shows an embodiment of a device for determining a lattice descriptor of a hologram.

[0111] Fig. 2a shows a flowchart of an exemplary procedure. Fig. 2b shows intensity spectra recorded in the procedure from Fig. 2a for a first direction of incidence.

[0112] Fig. 2c shows a transmission spectrum for a first incidence direction determined in the method from Fig. 2a based on the intensity spectra from Fig. 2b.

[0113] Fig. 2d shows a reference spectrum, the transmission spectrum from Fig. 2c and a diffraction efficiency spectrum determined on the basis of the reference spectrum and the transmission spectrum for a first incidence direction.

[0114] Fig. 2e shows diffraction efficiency spectra of the measured hologram for a variety of incidence directions, including the first incidence direction from Figs. 2b-2d.

[0115] Fig. 2f shows, in analogy to Fig. 1, the directions of incidence and emission of the lighting from Fig. 2e, as well as the equilibrium plane and perpendicular foot vector determined on the basis thereof.

[0116] Fig. 2g shows an exemplary diffraction efficiency spectrum with several local diffraction efficiency maxima as a function of the area of ​​the hologram.

[0117] Fig. 2h shows an exemplary lattice vector field that can be determined based on the steps shown in Fig. 2b-2g.

[0118] Fig. 3 shows a multitude of vectors per direction of incidence for an RGB hologram, which can be determined as described herein.

[0119] Fig. 4 shows, for two superimposed RGB holograms, a multitude of vectors per direction of incidence, which can be determined as described herein.

[0120] Fig. 5 shows, for an RGB hologram with a noise grating, a plurality of vectors per direction of incidence, for the hologram grating as well as for the noise grating, which can be determined as described herein. 5- Detailed description of preferred embodiments

[0121] Fig. 1a shows a schematic representation to illustrate the Bragg condition. The Bragg condition in periodic lattices with a distance d between adjacent lattice planes.

[0122] 2d sin(0) = mA with me Ho, the angle 9 between the grating plane and the incident or emerging light, and the wavelength A = — is, as described herein, well known. Fig. 1a shows that, according to the Bragg condition, an incident wave k t A wave striking a grating (schematically represented in Fig. 1a by horizontal gray grating planes) at an angle of incidence of 0 is reflected by the grating planes. The angle of reflection relative to the grating plane is also 0, and the wave vector kd describes the reflected wave. This occurs at all grating planes. The Bragg condition thus describes, for grating planes adjacent at a distance d, that constructive interference of the reflected waves occurs when 2d sin(0) = mA is satisfied.

[0123] While the Bragg condition represents the interaction of gratings with light in real space, the definition of the wave vector k = — A and the

[0124] (one-dimensional) reciprocal lattice vector K = The analogous Laue condition can be derived in reciprocal space: K = k d — k t for k t = —k d , where momentum is conserved | k d | = | k t | .

[0125] Fig. ib shows a schematic representation to illustrate the Laue condition, where the incident light k t is deflected from the hologram in the direction of kd, such that the difference in the wave vectors k d — k t = K. The reciprocal lattice vector K corresponds to where d is the lattice plane spacing.

[0126] Furthermore, Fig. ib shows the refraction effect on the light, which arises from the fact that the hologram substrate has an average refractive index that differs from the ambient refractive index. Specifically, the light incident on the hologram from the outside is kt (to t) refracted. Likewise, the (undeflected) zeroth order light k is refracted. t (to d0 ) as well as the deflected light k d (to dl ) upon exiting the hologram substrate. These refraction effects can be corrected as described herein to account for the deviation of the propagation directions of light within the hologram from those outside the hologram in determining the grating descriptor.

[0127] Fig. ic shows a schematic representation illustrating the Laue condition using the Ewald sphere. The representation of the Ewald sphere links real space and its reciprocal. The Ewald sphere vividly illustrates the Laue condition for constructive interference during scattering at a grating. Specifically, constructive interference occurs when the circle with radius k... twhere a first and a second grid point intersect. Then, in turn, the Laue condition K = k applies. d — k t fulfilled.

[0128] Fig. id shows a schematic representation in real space of the illumination of a hologram 10 in three directions of incidence 11, 12, 13, which lie on a conical surface. The conical surface of Fig. id is characterized by a

[0129] The cone has an opening angle β. The cone can be perpendicular to the surface of the hologram 10 or tilted relative to it. In Fig. id, it is tilted by α relative to the surface normal of the hologram 10 (parallel to the z-axis). The three exemplary directions of incidence differ in that they all lie on the cone's surface but at different angles γ (about the cone's axis of symmetry).

[0130] Fig. 1 shows in reciprocal space a schematic representation of the directions of incidence and reflection of the three lights 11, 12, 13 from Fig. 1, as well as a regression plane 20 and perpendicular foot vector F determined thereon. Fig. 1 further shows the vectors 21, 22, 23 determined on the basis of the three lights 11, 12, 13, which run along the respective direction of incidence of the associated light and whose respective magnitude, e.g. as described herein, can be k = - —, where extr the extra

[0131] The wavelength can be such that the transmission spectrum of the hologram has a minimum or the corresponding diffraction efficiency spectrum has its maximum for the respective direction of incidence. In the example of Fig. 1, the regression plane 20 extends such that it encompasses the three endpoints of the determined vectors 21, 22, 23, which start at the origin of the coordinate system. The foot-of-perpendicular vector F is then dropped from the origin of the coordinate system onto the regression plane in the example of Fig. 1.

[0132] Fig. 11 shows an embodiment of a device 100 for determining a grating descriptor of a hologram. The device of Fig. 11 comprises a base 140. In the example shown in Fig. 11, an exemplary means for automatically positioning and / or orienting the light source 110 is attached to the base 140. The means can comprise a first joint 111 (e.g., a rotational joint) that allows a pivot, e.g., by 2.n, and a second joint 112 (e.g., a rotational joint) that allows a tilting of the light source relative to the first joint 111 and the base 140 and / or a rotation, e.g., by 271, so that the illuminations 113, 113", 113" emitted by the light source can lie on a conical surface, as is shown by way of example for three positions of the light source 110, 110", 110". The optional first joint can, e.g.,pivot the axis of rotation of the cone surface around the point where the illuminations hit the hologram and / or around an axis of rotation perpendicular to the hologram surface.

[0133] In the example shown in Fig. 11, a means for automatically positioning and / or orienting the detector 120 along the at least three directions of incidence is attached to the base 140. This means comprises a first joint 121 (e.g., a rotation joint) that allows a pivot, e.g., by 2.n, and a second joint 122 (e.g., a rotation joint) that allows a tilt of the light source relative to the first joint 121 and the base 140 and / or a rotation by 2.71, so that the detector 120 can be moved along with the light source 110, ensuring that the detector 120 is always positioned substantially opposite the light source 110 for detection. The position of the detector 120 relative to the light source 110 and / or the hologram 10 can be corrected, e.g., at least partially, based on the refraction effect described herein.However, the correction is typically so small in relation to the size of the components of the device 100 that the detector 120, even in its corrected position, can be placed essentially opposite the light source 110. In some exemplary embodiments, the parallel displacement of the measuring beam caused by the refraction effect (e.g., by varying substrate thicknesses) can be ensured by a sufficiently large detector 120 or a detector 120 with a sufficiently large receiving aperture relative to the light source 110.

[0134] The device can include a traversing table for moving the hologram 10, which can determine the positioning of the hologram along at least one axis by means of at least one positioning stage. In the example of Fig. 1, the traversing table comprises two xyz positioning stages 130a, 130b, which are configured to move the hologram 10 relative to the base 140 and thus to the light source 110 and the detector 120. One of the two xyz positioning stages 130a, 130b can, for example, be configured as an active positioning stage and the other as a passive support, e.g., on the opposite side of the traversing table.

[0135] Fig. 2a shows a flowchart of an exemplary method 200 for determining a lattice descriptor of a hologram, comprising the sub-steps 210, 220, 230, 240, 250, 260, 270, and 280, which are described in detail herein. The process shown in Fig. 2a can be used to determine or measure (existing) lattice descriptors of the hologram.

[0136] Fig. 2b shows intensity spectra 220 recorded using the method from Fig. 2a (namely the dark line recorded, for example, with the light source switched off / D (d) 211, the sample measurement / H (d) 212, in which the hologram is illuminated by the lighting, and the reference spectrum / R(d) 213, in which illumination without a hologram is recorded in the measurement position) for a first direction of incidence. The dark line represents the zero values ​​as a function of wavelength. The reference spectrum 213 represents the spectrum emitted by the light source and detected by the detector. The sample measurement 212 represents the intensity according to the reference measurement 213, wherein the interaction of the hologram with the illumination modifies the spectrum insofar as the intensity of the transmitted light is reduced, e.g., by broadband absorption, refraction, scattering, etc., and / or, for the exemplary reflection hologram shown, preferably by narrowband holographic diffraction, which in the example of Fig. 2b ensures that light in the range of approximately 530 nm is almost completely deflected by the interaction with the hologram and therefore does not reach the detector. Fig. 2c shows a sample measurement in the method from Fig. 2a based on the intensity spectra from Fig.2b determined transmission spectrum T(A) 221 for the first incidence direction. This transmission spectrum 221 is calculated in step 220 using the formula T(A) = ( / . H (A) - / D (A)) / ( / R (A) - / D (A)) calculated. The exemplary transmission spectrum 221 has a minimum at approximately 530 nm.

[0137] Fig. 2d shows a reference spectrum R(A) 231, the transmission spectrum T(A) 221 from Fig. 2c, and a diffraction efficiency spectrum B(A) 232 for the first incidence direction, determined based on the reference spectrum 231 and the transmission spectrum 221. In step 230 shown in Fig. 2d, the diffraction efficiency spectrum 232 is calculated using the formula β(A) =

[0138] The reference spectrum 231 can be determined, for example, by fitting the edges of the transmission spectrum 221, for example, with a function that varies slowly as a function of wavelength compared to the transmission spectrum 221 (e.g., a polynomial). Alternatively, the reference spectrum can also be determined, for example, by a measurement without a sample and / or an (unstructured) sample that corresponds, for example, to the sample to be measured without an inscribed hologram.

[0139] Fig. 2e shows diffraction efficiency spectra of the measured hologram for a variety of incidence directions (expressed in Fig. 2e by the rotation angles -40°, -20°). 0, 0°, 20° and 40° of the rotation axis angle y from Fig. id), encompassing the first direction of incidence from Figs. 2b-2d at y = 0°. As exemplified in Fig. id, the measuring beam is rotated about the obliquely angled (by angle 0) rotation axis by the value of the rotation angle y. In an exemplary embodiment of the device for determining a lattice descriptor of a hologram, as shown, for example, in Fig. if, the rotation axis angle y does not have to correspond to the angle of incidence on the hologram: There, the incident beam (along y) can be rotated about the angled rotation axis, resulting in a rotated incident vector k. L This results in the angle of incidence 9 relative to the hologram normal n. z calculate: 9 = arccos ((n z■ i) / | ). A regression plane can be fitted to the ends of the wave vectors (originating from the origin), which can be determined for the angles as described, as described. The vector between the origin and the foot of the perpendicular to the plane can then represent half the reciprocal of the lattice vector as described.

[0140] The fact that the 40° transmission spectrum lies between the spectra for 0° and 20° suggests that the shortest distance to the regression plane is achieved between 0° and 40°. In other words, with an incident angle of 20°, the measuring beam most closely approximates the necessary Bragg condition K = 2k sin(0) of the inclined (holographic) grating, where (for wave vectors perpendicular to the grating planes) K = 2k, which corresponds to perpendicular reflection from the grating planes. From the definition of the wave vector k = — and / or the Bragg condition 2d sin(0) = mA, it follows that the wavelength A is maximal for 0° = 90° and sin(90°) = 1 and decreases with increasing and decreasing angles as the angle deviates from 0° = 90°. Therefore, the wavelength decreases again with increasing angle, or the corresponding wave vector becomes longer.Accordingly, the 40° transmission spectrum already has a shorter wavelength than the 20° transmission spectrum. The specified angle corresponds to the rotation angle y of the inclined axis of rotation, corresponding to the rotation along the conic section from Fig. id (and not 0). Essentially, in a three-dimensional representation, it becomes clear that the endpoints of the vectors described herein, determined for each direction of incidence and originating from the origin, span a plane, the so-called regression plane. More precisely, as explained, this plane is expected to be perpendicular to half the reciprocal wave vector K / 2 originating from the origin. The regression plane can be determined, for example, using fittings. In a later step, the perpendicular foot vector F from the origin 0 to the regression plane can be determined—for example, using various known mathematical methods.As described herein, at least one lattice descriptor can be determined by doubling the perpendicular foot vector: For example, the lattice descriptor can be determined in the form of the vector K = 2F, where K can represent the reciprocal lattice vector of the hologram or the associated lattice. Fig. 2f, analogous to Fig. 1, shows the incoming and outgoing directions of the illuminations from Fig. 2e, as well as the regression plane and perpendicular foot vector F determined based on these directions. In the example of Fig. 2f, five illuminations 11, 12, 13, 14, 15 are shown, along with their five corresponding vectors. Their endpoints are highlighted by circular markings.

[0141] Fig. 2g shows an exemplary diffraction efficiency spectrum with several local diffraction efficiency maxima as a function of the hologram area. The map in the upper section of Fig. 2g shows the scanned areas of the hologram. Each area can be associated with a specific diffraction efficiency spectrum and / or another spectrum described herein.

[0142] Based on the at least one lattice descriptor for the at least one region, a lattice vector field representing or characterizing the hologram can be estimated, calculated, and / or simulated. Fig. 2h shows an example lattice vector field that can be determined in step 270 based on the steps shown in Figs. 2b-2g.

[0143] Fig. 3 shows a multitude of vectors k for an RGB hologram. t,i 31, 32, 33 per direction of incidence, which can be determined as described herein. Specifically, for an RGB hologram, the vectors 31, which can be assigned to the deflection of red light, the vectors 32, which can be assigned to the deflection of green light, and the vectors 33, which can be assigned to the deflection of blue light, lie in one plane, so that three planes of regression can be determined: one for the R component of the hologram, one for the G component of the hologram, and one for the B component of the hologram. Based on this, three perpendicular foot point vectors F can then also be determined. r> F g> Fb can be determined, i.e., one per refractive index plane. The respective membership of the vectors in the R, G, or B grating can be determined via the respective wavelength of the transmission minimum or diffraction efficiency maximum and / or via analogous methods.

[0144] Fig. 4 shows a multitude of vectors k for two superimposed RGB holograms. t ,i per direction of incidence, which can be determined as described herein (see left image). Specifically, the corresponding hologram comprises six individual grids, such that the vectors k t The data can be divided into six groups 31, 32, 33, 34, 35, 36, each assigned to a grating contained in the hologram (see middle image). Based on this, six perpendicular foot point vectors Fi can then be determined (as shown in the right image), one for each grating. The assignment of the vectors to the respective grating can be determined via the respective wavelength of the transmission minimum or diffraction efficiency maximum and / or the relative orientation of the vectors to each other and / or via analogous methods.

[0145] Fig. 5 shows a multitude of vectors k for an RGB hologram with a noise grid. tThe values ​​for the direction of incidence, i, for the hologram grating as well as for the interference grating, can be determined as described herein. Specifically, it can be seen in the right-hand image that three groups of vectors 51, 52, 53 do not have the same relative orientation to each other as the remaining vectors assigned to the actual hologram grating. For example, this method allows interference gratings within the hologram grating to be found and characterized. This information can be valuable for improving the production of holograms, as it allows for precise knowledge of the errors that occur.

Claims

29 - August 2025 Carl Zeiss Jena GmbH Z17O784WO ANE / Ris / Mak REQUIREMENTS 1. Method (200) for determining a grating descriptor of a hologram (10), comprising: a) illuminating a first region of the hologram (10) with a light source (110) from at least three directions of incidence (11, 12, 13); b) detecting light (221) transmitted through the hologram (10) for each of the at least three directions of incidence (11, 12, 13); and c) determining a grating descriptor for the first region at least partially based on the detected transmitted light (221) and the respective direction of incidence (11, 12, 13).

2. Method (200) according to claim 1, wherein the illumination comprises polychromatic illumination of the first area of ​​the hologram (10).

3. Method (200) according to claim 2, wherein the polychromatic illumination comprises a first wavelength and a second wavelength, wherein the first wavelength differs from the second wavelength by 100 nm or more, preferably by 500 nm or more.

4. Method (200) according to one of claims 1-3, wherein at least two of the at least three directions of incidence (11, 12, 13) span a plane which is at an angle of at least 1°, preferably at least 10°, to at least one further of the at least three directions of incidence (11, 12, 13).

5. Method (200) according to one of claims 1-4, wherein the at least three directions of incidence (11, 12, 13) lie on a predetermined conical surface.

6. Method (200) according to one of claims 1-5, wherein the light (221) transmitted by the hologram (10) is detected substantially along the respective direction of incidence (11, 12, 13). 7- Method (200) according to one of claims 1-6, further comprising determining at least one local and / or global spectral transmission minimum along the respective direction of incidence (11, 12, 13).

8. Method (200) according to one of claims 1-7, further comprising a correction of the direction of incidence (11, 12, 13) of the illumination at least partially based on a refraction effect.

9. Method (200) according to claim 8, wherein the refraction effect comprises refraction at a surface of the hologram (10).

10. Method (200) according to any one of claims 1-9, wherein the at least one lattice descriptor comprises a reciprocal lattice vector (K) or a representation of the reciprocal lattice vector (K).

11. Method (200) according to any one of claims 1-10, wherein determining the at least one lattice descriptor comprises determining at least one vector (21, 22, 23) per direction of incidence (11, 12, 13), wherein preferably the direction of incidence (11, 12, 13) determines the direction of the vector (21, 22, 23), and / or wherein preferably the light (221) transmitted by the hologram (10) determines the magnitude of the vector (21, 22, 23).

12. Method (200) according to one of claims 1-11, wherein determining the at least one lattice descriptor comprises determining a leveling plane (20).

13. Method (200) according to claim 12, wherein determining the adjustment plane (20) comprises fitting the adjustment plane (20), preferably fitting it to the at least three vectors (21, 22, 23) according to claim 11.

14. Method (200) according to claim 7 or any one of claims 8-13, referring back to claim 7, wherein the determination of the at least one grating descriptor is based at least partially on the transmission minimum along the respective direction of incidence (11, 12, 13). 15- Method (200) according to one of claims 12-14, wherein determining the at least one lattice descriptor comprises determining a perpendicular foot point vector (F) to the regression plane (20).

16. Method (200) according to claim 15, wherein determining the at least one lattice descriptor comprises doubling the perpendicular foot point vector (F).

17. Method (200) according to one of claims 1-16, further comprising performing steps ac) for at least a second area of ​​the hologram (10).

18. Method (200) according to claim 17, further comprising repeatedly moving the hologram (10) relative to the light source (110) between the first region of the hologram (10) and the second region of the hologram (10) for the at least three directions of incidence (11, 12, 13); wherein the direction of incidence (11, 12, 13) is preferably constant during the movement; and / or wherein the direction of incidence (11, 12, 13) is preferably changed over time between the repeated movements.

19. Method (200) according to one of claims 1-18, wherein the first, second and preferably at least one further area are arranged in a regular and / or periodic grid relative to the hologram (10).

20. Method (200) according to any one of claims 1-19, wherein determining the at least one lattice descriptor comprises determining a plurality of lattice descriptors for a plurality of lattices.

21. Device (100) for determining a grating descriptor of a hologram (10), comprising: a light source (110) for illuminating a first area of ​​the hologram (10) from at least three directions of incidence (11, 12, 13); a detector (120) for detecting light (221) transmitted through the hologram (10) for each of the at least three directions of incidence (11, 12, 13); and a means (111, 112, 121, 122) for automatically positioning and / or orienting the light source (110) and / or the detector (120) along the at least three directions of incidence (11, 12, 13).

22. Device (100) according to claim 21, wherein the light source (110) comprises a pivotable holder (111, 112) and the pivotable holder (111, 112) is configured to pivot the light source (110) such that at least three directions of incidence (11, 12, 13) lie on a predetermined conical surface.

23. Device (100) according to claim 21 or 22, wherein the light source (110) further comprises an element for influencing the light emitted by the light source (110), wherein the element for influencing preferably comprises an autocollimation telescope.

24. Device (100) for measuring a hologram (10) which is configured to perform the steps of the method (200) according to any one of claims 1-20.

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