EP3516351A1

EP3516351A1 - Measuring device and methods for the characterization of a radiation field, more particularly of laser radiation

Info

Publication number: EP3516351A1
Application number: EP16781284.1A
Authority: EP
Inventors: Frank Killich; Uwe Engeland
Original assignee: Lavision Biotec GmbH
Current assignee: Lavision Biotec GmbH
Priority date: 2016-09-26
Filing date: 2016-09-26
Publication date: 2019-07-31
Also published as: WO2018054444A1; CN110023726B; US20210172794A1; CN110023726A; US20190250030A1; US11307086B2

Abstract

A radiation field measuring device (100) for the characterization of a radiation field (1) that passes through a medium (2) in a longitudinal direction (z) comprises a detector device (10) having at least one detector camera (11), which contains at least one detector array (12) for the image recording of stray radiation (3) that is generated in the medium by the radiation field (1) and is directed in a multiplicity of lateral directions that deviate from the longitudinal direction (z), and a reconstruction device (20) for the characterization of the radiation field (1), on the basis of image signals of the detector device (10), wherein the reconstruction device (20) is configured for the tomographic reconstruction of a field density of the stray radiation (3) in the radiation field (1). Uses of the radiation field measuring device and methods for the characterization of a radiation field (1) that passes through a medium (2) in a longitudinal direction (z) using the radiation field measuring device (100) are also described.

Description

Measuring device and method for characterizing a radiation field, in particular laser radiation

Technical area

The invention relates to a radiation field measuring device and method for characterizing a radiation field of electromagnetic radiation, in particular laser radiation, based on the detection of scattered radiation, which generates the radiation field in a medium. Applications of the invention are in the monitoring and / or control of radiation sources, in particular laser sources for the material processing, and of radiation-based methods, for. B. for material processing or measurement purposes given.

Background Art It is well known that the effectiveness and accuracy of radiation based methods, e.g. For material processing or measurement purposes, depending on the geometric characteristics and / or field characteristics of the radiation field used in the radiation-based method. For example, the effectiveness of material processing with laser radiation is influenced by the formation of a focus of the laser radiation on the surface of the material. There is therefore a general interest in investigating (measuring) radiation fields in order to detect their properties and, if necessary, to control a radiation source in such a way that the radiation field is generated with predetermined properties. Conventional methods for studying radiation fields include invasive methods and non-invasive methods. Invasive procedures, such as As the direct detection of the radiation field ^¬ with a camera, have the disadvantage that their application changes the radiation field to be examined. As a result, a desired effect of the radiation field may be impaired or even excluded at times.

For example, the online monitoring of laser cutting or welding systems should avoid influencing or destroying the light distribution of a working beam. Even if only a part of the radiation field to be examined is separated from a main beam and examined separately (see eg DE 101 49 823 A1), the optics used for the separation, eg. As by pollution, affect the application of the main beam.

Furthermore, invasive procedures are limited to the study of low power density radiation fields. Optics, such. As mirrors, prisms, filters and / or lenses, in the beam path of the radiation field to be examined can be destroyed at high power densities. For this reason, it is usually not possible, for. B. to directly examine the radiation field in the focus of laser radiation with an invasive procedure. Finally, invasive methods for measuring a radiation field, in particular in the case of monochromatic radiation (eg in the case of a cw laser), are prone to artifacts due to diffraction of defects or impurities on the optics, eg. B. lens surfaces, which can lead to interference, is hardly avoidable and the accuracy of the measurement impaired.

Non-invasive methods have the advantage that they are applicable in particular at high radiation intensities and that the radiation field to be examined by the measurement is not affected. For example, US 8 988 673 B2 describes a non-invasive method in which the scattered light of a laser beam, when passing through a gas, is picked up by a camera in order to measure the shape of the pharoid beam (of the entire beam). With the method ^¬ ser 2D images scattered radiation to be measured, which represent projections of the intensity distribution of the laser beam on planes parallel to the beam direction. The method according to US Pat. No. 8,988,673 B2 has the disadvantage that neither transaxial 2D sections nor SD volume reconstructions of the laser beam can be determined. With the method according to US Pat. No. 8,988,673 B2, a sequence of 2-D projections of the radiation field could be achieved, for example by the repeated movement of a camera along a predetermined linear profile. The measurement of a single

However, light pulses would not be possible.

A general problem of conventional techniques for investigating radiation fields is that they are limited to the detection of individual properties and are not suitable for a complete characterization of the radiation field by only one measurement. In particular, non-invasive methods for the simultaneous determination of several parameters of the radiation field, such. As intensity distribution, caustics, M ² parameters, beam propagation, wavefront, wavelength and polarization properties, and / or beam shape unknown. The simultaneous detection of several properties of the radiation field has hitherto only been achieved by the combination or temporally successive application of different measuring methods, which increases the complexity of the examination. Furthermore, several measurements can be made by their each ne ^¬ gativ affect respective influence of the radiation field, thereby impairing an accurate representation of the radiation field or even mutually exclusive. Finally, the use of temporally successive measurements would be limited to invariable radiation fields and, for the investigation, for B. of individual laser ^¬ pulses or of transient light distributions unsuitable.

Object of the invention

The object of the invention is to provide an improved radiation field measuring device and an improved method for characterizing a radiation field of electromagnetic radiation, in particular laser radiation, with which disadvantages of conventional techniques are avoided. The invention is intended in particular to enable non-invasively more properties of a radiation field capture, and / or characterize the radiation field with increased spatial resolution, accuracy and / or reproducibility, and / or to create new applications of characterization of a radiation field. Furthermore, in particular as complete as possible a measurement and reconstruction of the radiation field should be achieved by the application of only one measuring method as possible. This should be possible in particular by a single measurement or multiple time-resolved individual measurements. Furthermore, the radiation field measuring device should be distinguished, in particular, by a simplified technical structure and / or an extended field of application.

Summary of the invention

According to a first general aspect of the invention, said object is achieved by a radiation field Measuring device (also referred to as scatter radiation tomography) for the characterization of a radiation field which passes a medium in a longitudinal direction (beam direction) by ^¬, dissolved, the (graphie- tomography) a detector device and a reconstruction device comprises.

The detector device comprises at least one detector camera with at least one detector array, which is arranged for image acquisition of scattered radiation which is generated in the medium by the radiation field and in a plurality of side directions (rotational directions) is addressed, which differ from the Lon ^¬ gitudinalrichtung.

According to the invention, the reconstruction device for characterizing the radiation field by means of a computer-tomographic spatially resolved reconstruction (referred to here as tomographic reconstruction) of a field density (energy or power density, spatial distribution) of the scattered radiation in the radiation field using

Image signals of the detector device set up. The characterization of the radiation field generally comprises the determination of the field density of the scattered radiation and preferably the determination of beam parameters, in particular geometric beam parameters and / or field beam parameters, of the radiation field and / or the determination of a distribution of scattering particles in the medium.

The field density of the scattered radiation is a function of the intensity distribution in the radiation field and thus allows, in particular, the provision of the desired beam parameters.

The scattered radiation, if Rayleigh scattering is generated from a monochromatic radiation field, is proportional to the intensity distribution in the radiation field. In the case of a polychromatic radiation field results under the The prerequisite for the fact that the detected spectral distribution does not vary spatially in the measurement volume of the radiation field and, in particular, that the intensity I of the radiation field can be factored in accordance with I (λ, r) = Ιι (λ) * I ₂ (r), is also a proportionality. The latter requirement can z. B. can be met by the detector device is equipped with a spectrally selective effective filter, which passes a partial spectral range of the radiation field. If the intensity of the radiation field scattering is a linear function of the intensity of the radiation field, then, except for a calibration factor, the tomographic reconstruction based on the scattered radiation will give the 2D or 3D intensity distribution of the radiation field. In other littering processes, a quantitative relationship between the field density of the scattered radiation and the intensity distribution in the radiation field can also be determined by calibration measurements or application of scattering models.

According to a second general aspect of the invention, said object is achieved by the use of the radiation field measuring device according to the first general aspect of the invention in controlling a focus of the radiation field, detecting a temporal drift of an intensity profile of the radiation field, characterizing the radiation field of high-energy lasers, laser-assisted material processing in cutting and joining techniques, manufacturing in semiconductor technology, or therapy and / or surgery by means of laser radiation, and / or monitoring and / or

Control of radiation-based processes, eg. B. in the control of a radiation source, in particular a laser source solved. In particular, according to the second aspect of the invention, a control device for a radiation source is provided. In particular, the tomographic reconstruction apparatus considered as independent subject of the invention. According to a third general aspect of the invention, the object is achieved by a method for characterizing a radiation field, which passes through a medium in a longitudinal direction, using a radiation field measuring device according to the first general aspect of the invention, wherein an image acquisition of Scattering radiation generated in the medium by the radiation field and directed in a plurality of lateral directions deviating from the longitudinal direction by means of the detecting means, and characterization of the

Radiation field with the reconstruction device under

Use of image signals of the detector device are provided, and wherein the reconstruction device performs a tomographic spatially resolved reconstruction of the field density of the scattered radiation in the radiation field.

The invention generally enables the characterization of a directional radiation field incoherent radiation or coherent radiation (laser radiation). The characterization of laser radiation is preferably provided, as it favors a reconstruction of the field density of the scattered radiation with a high signal-to-noise ratio. The radiation field can be a continuous radiation field (continuous operation, cw operation) or a pulsed radiation field (pulse operation), whereby the power density and in pulsed operation the energy density of the scattered radiation is reconstructed as field density in continuous operation.

The scattered radiation is generated by the radiation field in the medium, which is generally a scattering substance, in particular at least least one gas (or steam), z. As air or other gaseous process medium or stray gas, a liquid, a solid, a plasma, or a particle containing together ^¬ mensetzung such. A colloidal solution, an aerosol, smoke, or an emulsion. Depending on the nature of the scattering medium, the scattered radiation z. B.

generated by Rayleigh scattering, Tyndall scattering, Mie scattering or scattering on free charge carriers. These scattering mechanisms are each characterized by a specific distribution of scattered radiation (e.g., shape of the lobe or orientation relative to the longitudinal direction of the radiation field) that can be taken into account in the tomographic reconstruction of the field density. The spatial characteristics of the scattered radiation can be determined by a calibration measurement.

The image signals of the detector device (scattered radiation images) provide projections of the scattered radiation in the detected lateral directions on the at least one detector array. The reconstruction device is configured to determine at least one sectional image of the scattered radiation in the radiation field from the scattered radiation images, which are recorded in accordance with a number of projections from several different directions (the detected lateral directions) by tomographic reconstruction. The sectional image of the scattered radiation represents the field density of the scattered radiation in the radiation field, in particular the spatial distribution of the scattered radiation in the radiation field, which is a qualitative and quantitative measure of the field distribution of the radiation field. The reconstruction device provides a three-dimensional model of the field distribution of the radiation field. Advantageously, the limitations of conventional techniques are avoided by the use of the scattered tomography scanner by the already occurring in the medium anyway

Scattered radiation, e.g. based on the Rayleigh scattering of the radiation field or fluorescence on atoms or molecules of the medium, is used to characterize the radiation field comprehensively and with only one measurement. In particular, the imperfections of the conventional scattered light imaging 2D method according to US 8 988 673 B2 are remedied by the tomographic radiation field reconstruction, and a complete radiation field reconstruction in a measuring section of interest is achieved without disturbing the radiation distribution. Furthermore, there are the following advantages of the invention. The scatter tomograph operates without contact, i. non-invasive, so that the radiation distribution to be examined is not influenced by the measurement. It is particularly advantageous that no dust particles and defects on optical components can have a disturbing effect, since there are no such optical components in the beam path of the radiation field to be examined. Particularly high radiation intensities can be measured without damaging components of the scattered tomography scanner. Alternatively, the scatter tomograph can be set up for an invasive operation, for example if the examined radiation field is to be rotated in the optical setup used for imaging the scattered radiation or if the examined radiation field is to be branched off from a main beam.

The invention enables a comprehensive measurement of the

Radiation field, in particular a three-dimensional reconstruction of the intensity profile of a radiation field in a measurement volume, and the derivative of a variety of

Beam parameters from this. The measurement can be carried out free of artifacts, in particular free from interferences, silhouettes and / or diffractions. The scatter tomograph allows the reconstruction of the intensity profile of the examined radiation field also for transient radiation fields and in particular once-only radiation pulses. Advantageously, several transient phenomena of the radiation field in a measuring volume can be recorded simultaneously. The scattered tomograph has a considerably simplified construction compared to the combination of conventional measuring arrangements, which would be required for comprehensive characterization of the radiation field. Advantageously, in contrast to the measured summation image in US Pat. No. 8,988,673 B2, the invention provides a tomographic reconstruction of the radiation field or its beam parameters. The characterization of the radiation field is independent of the direction of observation, since for the tomographic reconstruction anyway a multi-angled detection of the

Stray radiation images is provided. The complete three-dimensional reconstruction of the intensity profile in a measuring section makes it possible to derive freely selectable two-dimensional intensity profiles along any cutting planes through the medium in the measuring section.

A further advantage of the invention is that the characterization of the radiation field for radiation in different wavelength ranges is made possible. The term "radiation" refers in particular to electromagnetic radiation having a wavelength in the x-ray, UV, VIS, NIR, IR, or microwave range. Preferably, the detector device for image recording of the scattered radiation is respectively corresponding to a wavelength in the X-ray, UV, VIS, NIR, IR, or microwave range. Particular preference is given to characterizing laser radiation having a wavelength in the UV, VIS, NIR or IR range. But also for other wavelength ranges there are specific advantages. So, is based on allowing the emission generated during the Re ^¬ combination radiation, the measurement of Inten ^¬ sitätsverteilungen ionizing radiation such as X-ray or XUV / UV radiation, damage the conventional radiation detectors, or would destroy.

Soft X-ray radiation, which is characterized by the method according to the invention, preferably has an energy of 0.1 to 1 keV. For example, at a wavelength in the range of 1 nm to 10 nm, corresponding to about 1000 eV to 100 eV, the scattering and absorption in air is already comparable to the scattering of visible light in air. The characterization of X-ray radiation is e.g. for applications in the semiconductor industry, in particular for microlithography of interest, for which there are hitherto no suitable non-invasive beam diagnostic methods.

Preferably, the reconstruction device is set up for nonanalytical, in particular algebraic or statistical, tomographic reconstruction of the field density of the scattered radiation. Particularly preferably, the tomographic reconstruction of the field density of the scattered radiation comprises an iterative algorithm.

The tomographic reconstruction with a non-analytical method has advantages compared to analytical methods in the achievable quality and quantifiability of the reconstruction result, in particular by being calculated artifact-free and spatially resolved.

Non-analytical methods may e.g. For example, the targeted small projection number otherwise expected sampling artifacts in the reconstruction result wrestlers considerably ver ^¬. Furthermore, they allow in principle the Berücksichti ^¬ account all occurring in the course of Bildakquirierung, cherweise usual degrading the image quality, physical ef ^¬ fect. These may be, for example, the characteristic of the imaging system (the so-called point imaging function, PSF) or, for example, the occurrence of reflection scattered radiation. What is common to all non-analytical methods is that they discreetly perceive space from the outset, including the reconstruction result and the measurement data. That is, the reconstruction result to be determined is decomposed into a plurality of three-dimensional voxels by the discretization of the space; The measured data are correspondingly decomposed into a multiplicity of two-dimensional pixels.

A first subset of non-analytical reconstruction methods are algebraic reconstruction methods. They invert a linear equation system or determine its pseudoinverse (Moore-Penrose inverse). The multitude of algebraic reconstruction methods is carried out iteratively because of the high degree of complexity of the task, for example with the algorithms ART, MART, or SMART. Preferably, the tomographic reconstruction is performed with a second subset of the non-analytical reconstruction methods, namely the statistical reconstruction method. These are also performed essentially iteratively. They have particular advantages in the reconstruction based on noisy images of

Scattered radiation (measured data (y)). For example, the noise characteristic of the measured data, as may occur due to the low intensity of the scattered radiation, can be implicitly taken into account. Statistical procedures are based on the research mulation of a high-dimensional objective or cost function F (f), which assumes a minimum, at best global, minimum for a given choice of voxel values. The totality of precisely these voxel values, for which the cost functional is minimized, represents the reconstruction result f. There are a multiplicity of applicable ones depending on the type of formulation of the target function and the type of iterative calculation rule (of the algorithm) for the search of the target functional minimum statistical, iterative reconstruction methods.

The objective function F (f) consists of at least two components. The tomographic data mismatch term L (y_, f) formulating the imaging requires, within the noise characteristic of the measured data _, the correspondence of the forward projections of f, calculated by applying a system matrix A to f, f, with the measured values y. The system matrix A formulates the measurement geometry and, in principle, takes into account all the physical effects of the generation of measured values. The maximum likelihood term is preferably used as the tomographic data mismatch term, which takes into account the normally occurring Poisson noise characteristic of the scattered radiation.

The second component of the objective function is provided because the formulation of the objective function alone by the data mismatch term is a so-called ill-posed problem which, in the course of the iterative minimization process, generally results in noise enhancement of the reconstruction result. Therefore, the target functional is preferably complemented by a Bayesian regularization term R {f) based on prior knowledge of neighborhood ratios of the voxel values of the reconstruction result. The statistical tomographic reconstruction using the scattered radiation images is preferably carried out analogously to the tomographic reconstruction of emission tomographic measurement data, which is described in US Pat. No. 8,559,690. Accordingly, the target to be minimized ^¬ functionally is preferably supplemented by a third term. This is one, the sparseness or at least the compressibility of f amplifying Lp-norm term with (0 ^ p <2), in particular a Ll-norm term: || T ^r f || i. Since the compressibility of f is generally not given in space, f ^{T is transformed} into a sparse or at least compressed representation by means of T ^T , for example by using a three-dimensional wavelet transformation, which is further selected such that it is as incoherent as possible to the system matrix A _, is. The use of this term advantageously combines the compressive-sensing paradigm, which makes possible a considerable reduction in the number of individual measurements of the scattered radiation required for artifact-free reconstruction at different angles.

The objective function to be minimized is therefore preferably formulated as follows:

F (f) = L ( _Z , hf) + \\ X ^T f \\ i + R (f), α and β are factors that determine the effect of the respective target functional components. The algorithm to be used for minimizing the target function is arbitrary, as far as it adequately considers the numerically demanding L1-term. This concerns in particular the requirement according to which the voxel values must satisfy the boundary condition f> 0. Therefore, a so-called "Alternating Direction Method of Multipliers" (ADMM) algorithm is preferably used. The characterization of the radiation field comprises ^¬ preference, the determination of beam parameters in a particulate ^¬ free medium. Under practical conditions of use, however, dust particles in the measuring section can cause artifacts and disturbances in the reconstruction. When detecting Rayleigh scattering, it is therefore preferable to eliminate dust and Mie scattering events in the medium. Ge ^¬ Mäss a particularly advantageous embodiment of the dung OF INVENTION ^¬ is preferably a purely statistical approach to tektion de- and optionally, elimination of dust and Mie

Scatter events used in the medium. Several scattered radiation images are time-sequentially recorded ^¬ Lich and artifact pregnant scattering events that result from particles in the medium is eliminated by a statistical analysis of the series of scattered radiation images. This approach is thus based on an effective accounting of several, temporally successive individual measurements, and advantageously requires no predetermined parameters. According to an alternative variant of the invention, it may be provided to reconstruct the field density of the scattered radiation taking into account particles in the medium, which would lead to artefacts of the reconstructed field density without this consideration. Accordingly, for a temporally sufficiently sufficient radiation field, the measurement associated with each projection direction could be carried out several times. Transient scattering events, when the repetition frequency of the multiple measurement is matched to the mean moving velocity of the dust particles, are effectively eliminated by pixel-by-pixel median formation. At the same time, the projection images supplied to the tomographic reconstruction are emptied out. The application of the invention is not limited to the use of non-analytical methods. Alternatively, analytical methods can be used, which are characterized by the fact that they understand the reconstruction result and measurement data as continuous functions and solve a, implicitly simplify the Proj ektionsprozess, integral equation di ^¬ rectly. Examples are the filtered Rückprojekti ^¬ one (FBP) and the back-projection of filtered projections (CBP).

Advantageously, the tomographic reconstruction can be carried out in such a way that the illumination background, which may be determined by a reference measurement, is not subtracted from the scattered radiation images (projections) but is taken into account implicitly in a forward and backward reprocessing process of the tomographic reconstruction. The current illumination background may e.g. external illumination, if the medium in the measuring volume can not be completely shielded against external light,

and / or secondary scattering of Rayleigh scattering at objects in the vicinity of the measurement setup. In the latter case, the secondary scattering, which is outshined by the radiation field itself in the projection region of the radiation field, is estimated by interpolation in this projection region.

The lateral directions in which the scattered radiation images are taken are perpendicular to the longitudinal direction, in this case representing the radial directions, or at an angle of less than or greater than 90 ° relative to the longitudinal direction.

According to a further preferred embodiment of the invention, the at least one detector array for image recording of stray radiation is arranged such that the side angles are distributed such that the components of the recorded scatter radiation perpendicular to the longitudinal direction span a measuring range of 180 ° to 360 °. If the scattering medium on the way to the scattered radiation

Radiation field measuring device within and / or outside the radiation field homogeneous or inhomogeneous weakens, the detection of scattered radiation is preferably made of such selected lateral directions that their respective components are distributed perpendicular to the longitudinal direction of the radiation field over 360 °. If the attenuation of the scattered radiation by the scattering medium on the way to the radiation field measuring device is negligible, the detection of the scattered radiation is preferably carried out from side directions chosen such that their respective components are distributed perpendicular to the longitudinal direction of the radiation field over 180 °.

Preferably, the scattered radiation is measured in lateral directions, the components of which are arranged distributed uniformly perpendicular to the longitudinal direction over the measuring region, except in the case that it is an even number of lateral directions whose components are to be distributed perpendicular to the longitudinal direction over 360 ° , In this case, they are preferably distributed unevenly over the measuring range. Advantageously, the recording of redundant image information of the scattered radiation is thereby avoided, and the number of lateral directions which are required in a specific application of the invention for characterizing the radiation field can be minimized.

Advantageously, the characterization of the radiation field can be carried out using scattered radiation images which are displayed in only two different lateral directions (side angles not equal to 180 °, preferably around 90 °) were recorded. Alternatively, scattered radiation images along at least three side directions, in particular at least four (EI ^¬ nem measuring range of 180 °) or at least five was added (at a measuring range of 360 °) side directions and subjected to the tomographic reconstruction.

According to a preferred variant of the invention, the detector device is arranged perpendicular to the longitudinal direction for image recording of the scattered radiation. In this case, advantages may arise due to the available space and the adjustment of the detector device relative to the longitudinal direction. According to an alternative variant of the invention, the image recording can take place at an angle smaller or greater than 90 ° relative to the longitudinal direction, with advantages resulting from an increase in the scattering intensity when the angle of the lateral direction of the image recording decreases or increases relative to the longitudinal direction. If, according to a further embodiment of the invention, the detector device is configured for spectrally selective image acquisition of the scattered radiation, ie if scattered radiation images are recorded with the detector device only in a limited spectral range, there can be advantages for an improved suppression of interfering extraneous radiation and an improved signal-to-noise ratio. Ratio of reconstruction revealed. The detector device can be equipped with at least one suitable filter, for example, which reads through the desired spectral range. Another advantage of the spectrally selective image recording of the scattered radiation is the simplification of the reconstruction of polychromatic radiation fields. Advantageously, there are various possibilities, the field density in a measuring section of the examined

Radiation field to reconstruct. According to a first ^variant , a planar layer-shaped cutout (layer cutout) of the radiation field is detected. Since the layer has a finite thickness, the reconstructed field density is detected as a volumetric size. The slice section may be oriented perpendicularly or inclined relative to the longitudinal direction. The thickness of the slice section is preferably selected so that the field density within the slice is approximately constant. In this variant, the re ^¬ constructing means adapted for tomographic reconstruction of a transverse or inclined layer of the field density of the scattered radiation in the layer-neck finite thickness of the radiation field.

A conventional, invasive beam profiler generally measures a two-dimensional intensity distribution of the radiation field perpendicular to its longitudinal direction. The volumetric field density of the scattered radiation reconstructed according to the invention can, with a corresponding orientation of the layer, also be converted into a two-dimensional intensity distribution by the integration of the field density of each voxel in the longitudinal direction of the radiation field and the subsequent multiplication with a conversion factor.

The determination of the two-dimensional intensity distribution from only a single reconstructed layer of the field density of the scattered radiation has advantages in terms of the reduced equipment and computation outlay over a measurement and reconstruction extending over several layers. Thus, the detector device may preferably comprise line detector arrays with which linear scattered radiation images are recorded. the. This advantageously results in a simplified construction of the detector device.

According to a second variant, a three-dimensional, typically cylindrical or frustoconical, volume cut-out of the radiation field is detected, which consists of several layers of finite thickness or voxels arranged in a suitable manner of a suitable volume. In this case, the reconstruction device for the tomographic reconstruction of the field density of the scattered radiation in the entire three-dimensional volume section, which is constituted in each dimension by the juxtaposition of voxels, is set up. In this embodiment of the invention, the detector device preferably comprises area detector arrays. The volume cutout is composed, in particular, of at least two layered cut-outs which are arranged next to one another, preferably in the longitudinal direction. The volumetric cut-out can be distinguished by a field density which varies in the longitudinal direction.

Advantageously, there are also various options for configuring the detector device. According to a first variant, the detector device may comprise a plurality of detector cameras, which are each equipped with at least one detector array. In this case, an associated detector camera is provided for each side direction in which a scattered radiation image is to be recorded. Each detector camera provides a scattered image for one of the lateral directions, so that there are advantages if the scattered radiation images are to be recorded directly and without additional optical elements.

According to a second variant, the detector device may comprise a single detector camera which has a plurality of detectors. contains detector arrays, each for image acquisition of

Stray radiation are arranged in one of the lateral directions. The detector arrays can, for. B. separate arrays, z. B. CCD chips, or preferably portions of a common array, for. B. CCD chips include. This embodiment of the invention has the advantage of simplified construction and operation of the detector device.

If, according to a further preferred embodiment of the invention, a deflection device is provided which is arranged to deflect the scattered radiation along the plurality of lateral directions onto the plurality of detector cameras or the single detector camera, advantages for the positioning of the at least one detector camera, in particular with a distance and / or together on one side of the radiation field. The deflection device comprises optical elements, particularly preferably at least one catoptric element (in particular mirrors) and / or at least one dioptric element (in particular prisms and / or lenses) with which the beam path of the scattered radiation is spanned from one of the lateral directions to the associated detector camera becomes. The optical elements can be designed for imaging the scattered radiation on the at least one detector camera.

Advantageously, the deflection device can comprise a plurality of catoptical elements, in particular a plurality of reflector sections, which are each arranged to deflect the scattered radiation along one of the lateral directions toward one of the detector arrays. The reflector sections are preferably individual, planar or imaging mirrors or connected to an axicon reflector, which is arranged axially symmetrical to the longitudinal direction. The individual mirrors have advantages with regard to the optimizable adjustment of the individual NEN beam paths, while with the axicon reflector advantageously the measurement structure is simplified.

If the detector device comprises a single detector camera with a plurality of detector arrays, a collecting reflector is preferably provided as another catoptric element which collects beam paths from the lateral directions via the reflector sections and directs them to the detector camera. The collective reflector has the advantage that the adjustment of the detector camera is simplified relative to the reflector sections.

According to a further advantageous embodiment of the invention, the radiation field measuring device with a

Beam turning device to be equipped, which has a rotatable prism, in particular Dove prism, and / or a rotatable mirror and which is adapted to rotate the radiation field around the longitudinal direction. In this case, the detector device contains a single detector camera, which is arranged to record stray radiation. For the acquisition of scattered radiation images in the plurality of lateral directions, the radiation field is rotated with the beam rotator in different rotational positions relative to the detector camera. It is noted that this embodiment is designed for non-destructive measurement, i. it allows the simultaneity of measurement at the radiation field and primary application of the radiation field. However, this embodiment is only applicable to radiation field intensities that allow the use of the rotatable prism and / or mirror.

According to a particularly preferred embodiment of the invention, the characterization of the radiation field comprises the determination of beam parameters directly from the tomographic phically reconstructed field density of scattered radiation. Before ^¬ preferably an analyzer means is provided, which part of the reconstruction device or separately from this ^¬ attached is arranged and at least one beam parameter of the radiative field from the field density of the scattered radiation detected. Advantageously, at least one of the following beam parameters can be calculated with the analyzer device: Field beam parameters, such as eg. B. the pulse energy or pulse ^¬ energy density of the radiation field in the case of pulsed radiation, the field density of the radiation field in the case of kontinu ^¬ ierlicher radiation, coherence properties of the radiation field, wavefronts of the radiation field, Rayleigh lengths of the radiation field, or diffraction coefficients, M ² parameters and Beam propagation factors k of the radiation field, and / or geometrical beam parameters, such as geometric properties of the radiation field, in particular beam diameter, divergence angle and / or beam shape, properties of the beam waist of the radiation field, in particular radius, position along the longitudinal direction, and / or shape of the focus in transaxial cutting guide, and / or spatial position of the radiation field in the medium. Advantageously, the beam parameters can be determined individually, in subgroups or completely from a single measurement on the radiation field. If the analyzer device according to a further embodiment of the invention for a continuous determination of the at least one beam parameter and its temporal stability is established, there are advantages for the continuous monitoring of the radiation field and possibly the control of a beam source for generating the radiation field.

According to a further variant of the invention, the analyzer device can be used to calculate beam properties. be derived from the determined steel parameters. A preferred example is the calculation of the beam propagation, in particular by means of a wavefront analysis. The calculation of the beam propagation allows, in an investigation of the radiation field in a measuring section, which is spaced from a location of the action of the radiation field on a material, to determine beam parameters at the location of the action. For example, the focus of the radiation field can be characterized and the position of the focus can be detected, even if a recording of the scattered radiation images used for the tomographic reconstruction takes place outside the focus.

In accordance with a further advantageous embodiment of the invention, the radiation field measuring device can be equipped with a particle removal device which is set up to provide the medium in the measuring section of the radiation field measuring device in a particle-free state. The particle removal device has the advantage of removing dust particles from the measuring section, which could otherwise cause artifacts and disturbances of the reconstruction. Advantageously, various technical measures are available with which dust particles can be removed, such. As electrostatic filters, mechanical filters for generating a constant particle-free media flow through the measuring section, and / or Spülgasguellen to provide purified media or a purge gas for the measuring section. According to another application of the invention, the reconstruction of the field density of the scattered radiation can be used to determine a volumetric particle distribution in the radiation field. Advantageously, in this case, intermediate results of the reconstructed Information about the presence, the spatial distribution, the shape and the size distribution of scattering Parti ^¬ kel in the examined radiation field. From the latter, in turn, particle spectra can be derived.

According to a particularly preferred embodiment of the method according OF INVENTION ^¬ dung monitoring and / or controlling a radiation source are provided with which the examined radiation field is generated. Determined beam parameters of the radiation field are used to monitor the operating state of the radiation source and to adjust it if necessary and / or to stabilize it with a control loop. Preferably, the radiation source is a laser source, the z. B. for laser-assisted material processing in cutting and joining techniques or a manufacturing method in semiconductor technology or a laser-assisted surgical method is set up.

The setting and optional control of the radiation source can be z. B. the operation of a focusing of the

Radiation source in dependence on the determined position of the focus of the radiation field along the longitudinal direction comprise such that the focus on a predetermined working position, for. B. is set on the surface of a material to be machined.

Alternatively or additionally, the radiation source may include an adjusting device with the beam parameters of

Radiation field are variable, in which case the adjusting device in response to a determined

Beam parameter, particularly preferably in dependence on an intensity profile of the radiation field along the longitudinal direction, in particular in the focus of the radiation field, is controlled. Brief description of the drawings

Further details and advantages of the invention will be described below with reference to the accompanying drawings. They show schematically:

1 shows a preferred embodiment of the invention ^shown SEN radiation field measurement device ·

FIG. 2 shows an arrangement of reflector sections of the radiation field measuring device according to FIG. 1;

Figure 3: an arrangement of detector cameras for receiving

Scattered radiation images;

FIGS. 4 to 14 show features of further embodiments of the radiation field measuring device according to the invention with different variants of a deflection device;

FIG. 15 shows features of a radiation field measuring device with a beam turning device; and

FIG. 16 shows a flowchart with an illustration of features of preferred embodiments of the method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Features of preferred embodiments of the invention will be described below by way of example with reference to the investigation of radiation fields of light (light fields), e.g. B. continuous or pulsed laser light or non-coherent light, in particular in the UV, VIS or IR wavelength range include, described with the tomographic reconstruction using scattered light images. Optical elements of the radiation field measuring device according to include ^¬ special mirrors, lenses and / or prisms. However, the implementation of the invention in practice is not limited to the CHARACTERI ^¬ tion of light, but in accordance with radiation fields of other wavelengths, it is possible, for example, X-ray radiation. In these cases, the optical elements, if necessary, by appropriate elements for beam steering and / or

picture, such as X-ray optics, multilayer mirrors or grazing incidence mirror assemblies, and the detector camera (s) include e.g. CCD cameras with converter layers or cameras with image converter tubes. Furthermore, the radiation field measuring device and methods for its operation will be described in particular with reference to the collection of scattered light images and the structure of the detector device. Details of the reconstruction method can be realized as known from conventional methods of emission tomography, in particular according to US 8,559,690.

The collection of scattered light images can be done in preferred embodiments of the invention using a baffle with catoptric and / or dioptric elements. Features of embodiments of the invention with catoptric elements can accordingly also be realized by dioptre elements (and vice versa). For example, the effects of reflector portions can be realized by optical lenses. Katoptrische elements such. As mirror, however, have advantages because they have no color aberration and can be easily adapted to an elliptical arrangement with beam deflection. Multi-mirror arrangements with multiple reflector sections have also been similar to lens or prism arrays or the use of a single detector camera, the advantage of high solid angle coverage. 1 shows schematically a first embodiment of the radiation field-measuring device 100 for Cha ^¬ characterization of a light box 1 with a detector device 10, a deflection device 30 and a reconstruction means 20. In this embodiment the detector means 10 comprises a single detector camera 11. The

Radiation field measuring device 100 is provided for characterizing the light field 1 of a laser beam, which for the purpose of material processing with a laser source 210, z. As a C0 ₂ laser, a Nd-YAG laser or a disc laser, and is focused on the surface of a workpiece 220. For example, the mode structure and power of the light field 1 and the position of a focus on the surface of the workpiece 220 should be detected and possibly controlled. The light path of the light field 1 extends with a beam direction, which is referred to here as a longitudinal direction z, by a measuring section 4, the medium 2, z. As air contains. In the measuring section 4, the light field 1 has a cross-sectional dimension of eg 10 .mu.m to 10 cm, typically from 1 mm to 10 mm.

FIG. 1 shows the examination of the light field 1, which is generated directly by the laser source 210. Alternatively, if the field density of the radiation is sufficiently low, the light field 1 can be branched off with a beam splitter from a main beam which is directed onto the material to be processed.

The light field 1 is scattered on the molecules of the medium 2, so that scattered light 3 is generated. The scattered light 3 is in and against the longitudinal direction z and laterally emitted to it with components in the xy plane. Part of the scattered light 3 is collected at predetermined lateral directions with the deflector 30 (see FIG. 2A) and directed toward the detector camera 11 of the detector device 10. With the detector camera 11 scattered light images 6 of the im

Light field 1 generated scattered light 3 along the lateral directions recorded (see Figure 2B). The deflection device 30 comprises reflector sections 31 and a collection reflector 32 in the form of plane mirrors, which are inclined in the illustrated example relative to the longitudinal direction z by 45 °. There are z. B. four reflector portions 31 are provided, which reflect light 3 from the light field 1 in four lateral directions 5 to the collecting reflector 32. The side directions 5 are preferably distributed non-uniformly with respect to the x-y plane with different side angles, as shown schematically in FIG. 2A. From each reflector section 31, an image of the scattered light 3 generated in the light field 1 is reflected via the collecting reflector 32 to the detector camera 11. The reflector sections 31 have advantages for the prevention of background noise from secondary scattering, since the latter is guided out of the arrangement of the reflector sections 31.

The detector device 10 comprises a single detector camera 11 with a detector array 12, for example a CCD chip of the type Sony ICX285, and a camera objective 13. The scattered light images 6 can be recorded with a uniform detector array 12. Pixel groups of the detector array 12 provide a plurality of line detector arrays or multiple area detector arrays for imaging the scattered light 3. Alternatively, individual, separate detector arrays may be provided for imaging the scattered light 3. For one spectrally selective image pickup of the scattered light 3, the detector device 10 with a color-sensitive Detek- torarray 12 and / or a spectrally selective Filtereinrich ^¬ device (not shown) to be equipped. The detector camera 11 forms the two-dimensional intensity distribution of the scattered light 3 in the region of the light field 1 with the camera objective 13 via the plane mirrors of the reflector sections 31 and the collecting reflector 32. The boundary lines of the scattered light 3 give an impression of the Pharoidstrahlengang the camera field of view. In this case, on the detector array 12 on the different mirrors several views of

Scattered light from the light field 1 shown from different lateral directions. As shown schematically in Figure 2B, with the camera lens 13, e.g. generates four stray light images 6 on the detector array 12. The detector camera 11 supplies an image signal representing the scattered light images 6 to the reconstruction device 20.

The reconstruction device 20 comprises a computer unit which is designed to carry out a computer tomographic reconstruction process on the basis of the image signals of the detector camera 11. The reconstruction device 20 calculates the field density of the scattered light 3 in the light field 1 from the scattered light images 6 and the known geometry of the deflection device 30, in particular the distribution of the side angles 5 of the reflector sections 31.

The tomographic reconstruction yields a three-dimensional model (3D dataset z) of the intensity distribution of the

Scattered light 3 in the illustrated volume range of the light field 1. This three-dimensional intensity distribution of the scattered light 3 is a function of the local radiation intensity of the light field to be measured. The model of the intensity distribution characterizes the spatial brightness distribution. development of the light field, and it contains advantageously we ^¬ sentlich more information about the light field 1 than any of the projective two-dimensional camera views and more than one series of two-dimensional Intensitätspro ections of the measurement range of the light box 1, which can be measured according to US 8,988,673 B2 and even more than a series of in ^¬ vasiv and directly measured intensity profiles with a perpendicular to the z-axis imaging detector. FIG. 1 furthermore illustrates that the reconstruction device 20 can be equipped with an analyzer device 21 and a display device. With the analyzer device 21, by using the three-dimensional field density of the scattered light 3 in the light field 1 further

Beam parameters, such. B. the intensity or the position of the focus can be calculated. The determined beam parameters as error quantities can be used to control the laser source 210 to set predetermined beam parameters, the z. B. by a control device 50 shown schematically.

Features of a further embodiment of the radiation field measuring device with a detector device 10 which has a plurality of detector cameras 11 (multiple camera arrangement) are shown schematically in FIG. The detector cameras 11 are arranged uniformly distributed around the light field 1 in radial directions. Alternatively, an uneven distribution of the detector cameras 11 may be provided. Each of the detector cameras 11 is arranged to receive a scattered light image of the light field 1. In this case, the deflection device 30 shown in FIG. 1 can be dispensed with. Instead of a plurality of partial images on the detector array 12 (FIG. 2B), a plurality of individual camera images arise from different lateral directions. The image signals of the detector cameras 11 are subjected in a reconstruction device (not shown in Figure 3) of the tomographic reconstruction.

FIG. 4 shows a variant of the embodiment of the radiation field measuring device 100 according to the invention with a single detector camera 11 (FIG. 1), the arrangement of reflector sections 31 of the deflection device 30 being replaced by an axicon reflector 33 (individual hollow cone-shaped reflector). The axicon reflector 33 is designed so that numerous images of the scattered light 3 from the light field 1 from different lateral directions are imaged on the detector array 12. The use of the axicon reflector 33 provides further advantages in connection with compressive sensing (CS), since the axicon measurements take into account the "incoherence" required in the CS sense insofar as they project the scattered radiation of the radiation field along its longitudinal extension in the beam direction Notwithstanding Figure 4, the axicon reflector 33 can be replaced by two axicon subreflectors by halving the axicon reflector 33 in the longitudinal direction of the light field 1 and assembling the halves, wherein a partial reflector rotated by 180 ° This variant of the invention can provide advantages by balancing the uneven spatial resolution possible on the axicon reflector 33.

A further variant of the radiation field measuring device 100 with a single detector camera 11 is shown in FIG. 5, wherein the axicon reflector is replaced by an arrangement of strip-shaped plane mirrors 34 which are fan-shaped on a hollow cone surface. In this case, numerous images of the scattered light 3 are formed on the detector array 12 of the light field 1 generated from different lateral directions.

FIGS. 6 and 7 illustrate the application of the embodiment according to FIG. 5 in the characterization of a non-collimated light field 1. The diameter of the light field 1 passes through a minimum at a focus 7. According to FIG. 6, the deflecting device 3 deflects the scattered light 3 from the measuring section 4, which contains the focus 7, to the detector camera 11. The tomographic reconstruction of the field density of the scattered light 3 in the light field 1 directly provides a characterization of the focus 7. Alternatively, the scattered light 3 can be detected in a measuring section 4 with a distance from the focus 7, as shown in FIG. The three-dimensional reconstruction of the field density of the scattered light 3 enables a wavefront analysis and a detection of the propagation properties of the light field 1, in particular of its geometric shape, and thus indirectly also provides a characterization of the focus 7 and its position. The embodiment of FIG. 7 may be modified to the effect that the focus 7 is located outside the deflection device 30. Advantageously, it can contactless and non-invasive focus 7 z. B. on the surface of a material to be processed.

Features of modified embodiments of a radiation field measuring device according to the invention are shown in FIGS. 8A and 8B, wherein the longitudinal direction z of the light field 1 extends perpendicular to the plane of the drawing. In both cases, a deflection device 30 with a plurality of reflector sections 31 (plane mirror) is provided, which deflects scattered light 3 from the light field 1 to the detector camera 11 of the detector device 10. There are z. B. four reflector sections 31 is provided. The reflector portions 31 are arranged with surfaces parallel to the longitudinal direction z so that a center line of a tangent line of each reflector portion 31 of an ellipse in the xy plane, with the detector camera 11 (Figure 8A) or an imaging ^¬ objective in a focus of the ellipse 14 of a flexible or rigid Bildleitfaserbündels 15 (Figure 8B) and in the other focus the light field 1 are located. Together with the direct camera perspective on the light field 1, there are five different lateral directions and correspondingly five different scattered light images. According to FIG. 8A, the stray-light images are simultaneously recorded directly via the camera objective 13 with the detector camera 11. According to FIG. 8B, the scattered-light images are recorded via the imaging objective 14, the image-guide fiber bundle (fiber-optic bundle with ordered fibers) 15 and a relay optics 16 with the detector camera 11 without an objective. The image signals of the detector camera 11 including the scattered light images are supplied to the reconstruction device (not shown).

The embodiment according to FIG. 8B has the advantage that the detector camera 11 can be arranged at a distance from the measuring section 4, so that disturbing conditions in the measuring section 4, such as, for example, are produced. B. electromagnetic interference fields or extreme temperatures, not affect the detector camera 11.

The planar reflector sections 31 of FIGS. 8A and 8B can be replaced by curved reflector sections 31, as illustrated by way of example in FIGS. 9 and 10. The aspherically curved reflector sections 31, which preferably comprise extra-axial ellipsoids or paraboloids, have an imaging and light-gathering effect. The curved ones Reflector sections 31 are arranged with their center lines on the ellipse described above with reference to FIG. Stray light 3 from the light field 1 is imaged on a single detector camera 11 with an entocentric objective 13 (FIG. 9) or on two detector cameras 11 with entocentric objectives 13 (FIG. 10).

The curved reflector portions 31 have an effect such as a field lens (or a field mirror) provided in object-side telecentric lenses between the object and the camera. In particular, telecentric here means that there are no distance-related magnification changes. The internal aperture for the purpose of enforcing telecentricity which is typical for telecentric objectives is not shown in FIG. The advantages of the arrangement of the curved reflector sections 31 as field mirrors consist first of all in the high numerical aperture of the imaging optics formed by the reflector sections 31 and the increased light intensity and secondly in the telecentric effect on the side of the light field 1 to be measured. Advantageously, this allows a smaller distance-dependent distortion in comparison with simpler arrangements with plane mirrors or with multi-camera arrangements according to FIG. 3. The object-side telecentric imaging of the scattered light 3 can, by design, result in a reduction of the light intensity. In order to compensate for this, the arrangement of the reflector sections 31 according to FIG. 9 can be modified such that a compromise is achieved on the one hand with sufficiently high light collecting capacity and sufficient depth of field and on the other hand with sufficient telecentricity. According to a further modification of the embodiment of Figure 9, the reflector sections 31 could be replaced by an axicon reflector with elliptical curvature. Embodiments of the invention in which the deflection device 30 comprises dioptric elements, in particular lenses 35, 36 and / or prisms 37, are illustrated in FIGS. 11 and 12. Figure 11 shows the deflection device 30 with two lenses 35, 36, the z. B. made of quartz glass and together with the lens of the detector camera 11 form an F-theta arrangement. Similar to the axicon reflector, the lenses 35, 36 provide a continuous image containing scattered light 3 from all detected side angles side by side, and the individual scattered tomographic reconstruction tomograms are computationally extracted from the continuous image. Advantageously, a larger angular range of the scattered light 3 is detected by the light field 1 by the F-theta arrangement in FIG. 11 than by the multiprism 37, which only images scattered light 3 in a maximum of a half-space of 180 ° or less (FIG. 12). Furthermore, an object-side telecentric image can also be realized with the F-theta arrangement.

According to FIG. 12, the deflection device 30 is provided with a multi-prism 37 z. B. of quartz glass, which is shaped to image five side angles (perspectives). The arrangement according to FIG. 12 can be advantageous if the radiation field measuring device, e.g. for reasons of space, should be arranged only on one side next to the light field 1 to be examined.

Figures 13 and 14 illustrate further embodiments of the invention, in which the deflector 30 dioptric elements in the form of a simple prism 38 or a Multiprismas 39, the z. B. made of quartz glass, comprises. Stray light 3 from the light field 1 is directed via the prism 38 or the Multiprisma 39 to the detector camera 11, whose Image signal to the reconstruction device (not shown) is supplied. These embodiments have advantages due to the simple structure of the deflector 30. The damage threshold of an optical element depends on the material of the optical element and is for quartz glass for continuous laser light, for example 1 MW / cm ² or for pulsed laser light (10 ns pulse duration, laser intensity at 1064 nm:

20J / cm ² , pulse repetition frequency 100 Hz.) Eg 1 to 5 GW / cm ² . If the field density of the examined light field 1 is below the damage threshold of optical elements, in particular of glass, the beam rotator 40 shown in FIG. 15 can be provided with a rotatable dove prism 41 (or with rotatable mirrors, not shown) to communicate with the detector - Torkamera 11 scattered light 3 corresponding to different lateral directions to capture. With the rotatably mounted dove prism 41, the light field 1 generated by the laser source 210 can be rotated about the longitudinal direction z, wherein an image is taken for each set rotational angle. Furthermore, a background screen 17 is provided, the z. B. includes a blackened metal or plastic plate and a dark background for the camera image behind the

Light field 1 forms, which largely prevents reflections of the incoming light scattered light.

Advantageously, the dove prism 41 does not change the beam direction, but rotates itself about the beam axis z by an angle. The laterally emerging light field 1 rotates at twice the angle. In order to rotate the light field 1 by 360 °, the dove prism 41 is rotated by 180 °.

In this case, the detector camera 11 can record scattered light images with a freely selectable number of perspectives of the light field 1. Advantageously, the background remains constant for all lateral directions in this measurement geometry. FIG. 16 schematically illustrates the steps of the method for characterizing a light field 1 that passes through a medium 2. In the medium 2, the generation of scattered light by Rayleigh scattering of the light field 1 takes place at atoms or Mo ^¬ molecules of the medium 2. The intensity of the Rayleigh scattering IR results according to

IR = Io (k / λ ⁴ ) (1 + cos ² ©) from the intensity of the light field Io, a constant k, the wavelength λ and the angle Θ relative to the longitudinal direction of the light field. Accordingly, in addition to obtaining information about the intensity of the light field Io, the wavelength dependence of the scattered light can also be exploited in order to characterize the light field 1. Stray light images of the generated scattered light are recorded at different side angles relative to the longitudinal direction of the light field. The scattered light images provide projections of the scattered light generated by the light field 1, which undergo the tomographic reconstruction. As a result, the 2D or 3D field density of the scattered light in the light field 1 is calculated, followed by an analysis for determining characteristics of the light field, such as the light field. B. the beam profile or the shape of the wavefront.

The features of the invention disclosed in the foregoing description, drawings and claims may be significant to the realization of the invention in its various forms both individually and in combination or in sub-combination.

Claims

Claims 1. A radiation field measuring device (100) configured to characterize a radiation field (1) passing through a medium (2) in a longitudinal direction (z), comprising:

a detector device (10) with at least one detector camera (11) which contains at least one detector array (12) which is arranged to record scattered radiation (3) which is generated in the medium by the radiation field (1) and into one Variety of lateral directions is directed, which deviate from the longitudinal direction (z), and

a reconstruction device (20) which is set up to characterize the radiation field (1) based on image signals of the detector device (10),

characterized in that

- The reconstruction device (20) for the tomographic reconstruction of a field density of the scattered radiation (3) in

Radiation field (1) is set up.

2. Radiation field measuring device according to claim 1, wherein

- The reconstruction device (20) for non-analytical, in particular statistical or algebraic, tomographic reconstruction of the field density of the scattered radiation (3) is set up.

3. Radiation field measuring device according to claim 2, wherein

- The reconstruction device (20) for tomographic reconstruction of the field density of the scattered radiation (3) is set up by means of an iterative algorithm.

4. Radiation field measuring device according to claim 2 or 3, wherein

- The reconstruction device (20) for the statistical tomographic reconstruction of the field density of the scattered radiation

(3) is set up, wherein

the statistical tomographic reconstruction is based on a statistical model with a target function to be minimized, whose tomographic data mismatch term takes into account the noise characteristic of the measurement data.

5. Radiation field measuring device according to claim 4, wherein

(3) is set up based on the target function to be minimized, which contains an Lp norm term with (0 ^ p <2) and / or a Bayesian regularization term.

6. Radiation field measuring device according to one of the preceding claims, wherein

- The at least one detector array (12) for image recording of scattered radiation (3) is arranged such that the side angles are distributed such that the perpendicular to the longitudinal direction (z) extending components of the recorded scattered radiation (3) has a measuring range of 180 ° to Span 360 °.

7. Radiation field measuring device according to claim 6, wherein

- The at least one detector array (12) for image recording of scattered radiation (3) is arranged such that the perpendicular to the longitudinal direction (z) extending components of the recorded scattered radiation (3) with an even number of Side directions and a measuring range over 360 ° unevenly distributed, otherwise evenly distributed.

8. Radiation field measuring device according to one of the preceding claims, in which

- The detector device (10) for image acquisition of

Scattered radiation (3) in at least 2 lateral directions, in particular ^¬ special at least 3 lateral directions, is configured.

9. radiation field measuring device according to one of the preceding claims, wherein

- The detector device (10) for image acquisition of

Scatter radiation (3) is arranged in radial directions.

10. Radiation field measuring device according to one of the preceding claims, wherein

- The detector device (10) for a spectrally selective image recording of the scattered radiation (3) is configured.

11. Radiation field measuring device according to one of the preceding claims, wherein

- The reconstruction device (20) for tomographic reconstruction of a slice section of the field density of the scattered radiation (3) is arranged, which in a two-dimensional intensity distribution of the radiation field (1) can be converted.

12. Radiation field measuring device according to claim 11, wherein

- The detector device (10) line detector arrays (12) summarizes.

13. Radiation field measuring device according to one of claims 1 to 10, wherein

- The reconstruction device (20) for tomographic re ^¬ construction of the field density of the scattered radiation (3) in a three-dimensional volume cutout, which comprises at least two, juxtaposed layer cutouts is set up.

14. Radiation field measuring device according to claim 13, wherein

- The detector device (10) area detector arrays (12).

15. Radiation field measuring device according to one of the preceding claims, in which

- The detector device (10) comprises a plurality of detector cameras (11) each having at least one detector array (12).

16. Radiation field measuring device according to one of claims 1 to 14, in which

- The detector device (10) comprises a single detector camera (11), which contains a plurality of detector arrays (12) which are each arranged for image recording of scattered radiation (3) in one of the lateral directions.

17. Radiation field measuring device according to one of claims 15 or 16, wherein

- A deflection device (30) is provided, which is arranged for the deflection of the scattered radiation (3) along the plurality of side directions on the at least one detector camera (11).

18. Radiation field measuring device according to claim 17, wherein

- The deflection device (30) comprises at least one catoptric element (31, 32, 33) and / or at least one dioptric element (35).

19. A radiation field measuring device according to claim 18, wherein

- The at least one catoptric element comprises a plurality of reflector sections (31, 33), each for deflecting the

Scattered radiation (3) along one of the side directions towards one of the detector arrays (12) are arranged.

20. Radiation field measuring device according to claim 19, wherein

- The detector device (10) comprises a single detector camera (11), and

- The at least one catoptric element comprises a collecting reflector (32) arranged to deflect the scattered radiation (3) from the reflector sections (31, 33) to the detector camera (11).

21. Radiation field measuring device according to claim 19 or 20, wherein

- The reflector sections individual mirror (31) or one

Axicon reflector (33) comprise, which is arranged axially symmetrical to the longitudinal direction (z).

22. Radiation field measuring device according to one of the preceding claims, comprising

- A beam rotator (40) with a rotatable prism, in particular Dove prism (41), and / or mirror, which is arranged for rotation of the radiation field (1) about the longitudinal direction (z), wherein - The detector device (10) comprises a single detector camera (11), which is arranged for image recording of scattered radiation (3), and

- For image recording of scattered radiation (3) in the plurality of side directions, the radiation field (1) with the Strahldre ^¬ heinrichtung in different rotational positions relative to the detector camera (11) is rotatable.

23. Radiation field measuring device according to one of the preceding claims, in which

- An analyzer device (21) is provided, which is adapted to determine at least one beam parameter of the radiation field (1), based on the field density of the scattered radiation (3).

24. Radiation field measuring device according to claim 23, wherein

- The analyzer device (21) is arranged to determine at least one of the beam parameters, which include

Pulse energy or pulse energy density of the radiation field (1) in the case of a pulsed radiation field (1),

Field density of the radiation field (1) in a continuous radiation field (1),

geometric properties of the radiation field (1), in particular beam diameter, divergence angle and / or beam shape,

Properties of the beam waist of the radiation field (1), in particular radius, position along the longitudinal direction (z), and / or shape of the focus in transaxial

Cut,

spatial position of the radiation field (1) in the medium (2), coherence properties of the radiation field (1),

Wave fronts of the radiation field (1),

Rayleigh lengths of the radiation field (1), and Diffraction indices, M ² and beam propagation factors k of the radiation field (1).

25. Radiation field measuring device according to claim 23 or 24, wherein

- The analyzer device (21) is set up for a temporally continuous determination of the at least one beam parameter and its temporal stability.

26. A radiation field measuring device according to claim 24 or 25, wherein

- The analyzer device (21) for calculating a beam propagation, in particular by means of a wavefront analysis, is set up.

27. Radiation field measuring device according to claim 26, wherein

- The analyzer device (21) for calculating a focus position of the radiation field (1) is set up.

28. Radiation field measuring device according to one of the preceding claims, wherein

- A particle removal device (50) is provided which is adapted to provide the medium (2) in the radiation field measuring device (100) in a particle-free state.

29. Radiation field measuring device according to claim 28, wherein

- The particle removal device (50) comprises at least one of an electrostatic filter, a mechanical filter and a Spülgasque.lle.

30. Radiation field measuring device according to one of the preceding claims, wherein

- The detector device (10) for imaging the scattered radiation (3) having a wavelength in the X-ray, UV, VIS, NIR, IR or microwave range is set up.

31. Use of the radiation field measuring device (100) according to one of the preceding claims

in the monitoring and / or control of radiation-based processes, in particular in the control of a focus of

Radiation field (1), detection of a temporal drift of an intensity profile of the radiation field (1), characterization of the radiation field of high-energy lasers, laser-assisted material processing in cutting and joining techniques, manufacturing in semiconductor technology, or therapy and / or surgery by means of laser radiation.

32. A method for characterizing a radiation field (1), which passes through a medium (2) in a longitudinal direction (z), using a radiation field measuring device (100) according to one of claims 1 to 30, comprising the steps:

- Image recording of scattered radiation (3), which is generated in the medium (2) by the radiation field (1) and is directed in a plurality of lateral directions, which deviate from the longitudinal direction (z), by means of the detector means (10), and

- Characterization of the radiation field (1) with the reconstruction device (20) using image signals of the detector device (10), wherein

the reconstruction device (20) has a tomographic reconstruction of a field density of the scattered radiation (3) in

Radiation field (1) executes.

33. The method according to claim 32, wherein

- The reconstruction device (20) carries out a non-analytical, in particular statistical or algebraic, tomographic reconstruction of the field density of the scattered radiation (3).

34. The method according to claim 33, wherein

- The reconstruction device (20) performs the tomographic Re ^¬ construction of the field density of the scattered radiation (3) by means of an iterative algorithm.

35. The method according to claim 33 or 34, wherein

- The reconstruction device (20) performs a statistical tomographic reconstruction of the field density of the scattered radiation (3), wherein

36. The method according to claim 35, wherein

- The objective functional contains an Lp norm term with (0 ^ p <2) and / or a Bayesian regularization term.

37. The method according to any one of claims 32 to 36, wherein

- The image of scattered radiation (3) is such that the side angles are distributed such that the perpendicular to the longitudinal direction (z) extending components of the recorded scattered radiation (3) span a measuring range of 180 ° to 360 °.

38. The method according to claim 37, wherein

- The image of scattered radiation (3) is such that the perpendicular to the longitudinal direction (z) extending Components of the recorded scattered radiation (3) with an even number of lateral directions and a measuring range over 360 ° unevenly distributed, otherwise evenly distributed ver ^¬ are arranged.

39. The method according to any one of claims 32 to 38, wherein the image recording of scattered radiation (3) in at least 2

Side directions, in particular at least 3 lateral directions takes place, and / or

- The image is spectrally selective.

40. The method according to any one of claims 32 to 39, wherein

- The field density of the scattered radiation (3) is reconstructed taking into account a lighting background of the radiation field (1) in the forward and Rückwärtproj ektionsprozess the tomographic reconstruction.

41. The method according to any one of claims 32 to 40, comprising the steps

- Tomographic reconstruction of a slice section of the field density of the scattered radiation (3), and

- conversion of the field density of the scattered radiation (3) into a two-dimensional intensity distribution of the radiation field (1)

42. The method according to any one of claims 32 to 40, with the step

tomographic reconstruction of a field density of

Scattered radiation (3) in a three-dimensional volume cutout, which comprises at least two layered cutouts arranged one next to the other.

43. The method according to any one of claims 32 to 42, with the step

- Distraction of the scattered radiation (3) along the plurality of lateral directions with the deflector (30) on the at least one detector camera (11).

44. The method according to any one of claims 32 to 43, comprising the steps

Rotation of the radiation field (1) about the longitudinal direction (z) with the beam turning device, and

- Image of the scattered radiation (3) with a single detector camera (11), wherein

- For image recording of the scattered radiation (3) in the plurality of lateral directions of the radiation field (1) with the Strahldreh- device in different rotational positions relative to the detector camera (11) is rotated.

45. The method according to any one of claims 32 to 44, with the step

Detecting an intensity distribution of the radiation field (1), based on the reconstructed field density of

Scattered radiation (3).

46. The method of claim 32, further comprising the step of detecting at least one of the beam parameters that comprise

Field density of the radiation field (1) in the case of a continuous radiation field (1),

geometric properties of the radiation field (1), in particular beam diameter, divergence angle and / or beam shape, Properties of the beam waist of the radiation field (1), in particular radius, position along the longitudinal direction (z), and / or shape of the focus in transaxial

Cut,

spatial position of the radiation field (1) in the medium (2),

Coherence properties of the radiation field (1),

Wave fronts of the radiation field (1),

Rayleigh lengths of the radiation field (1), and

Diffraction indices, M ² and beam propagation factors k of the radiation field (1).

47. The method according to any one of claims 45 to 46, wherein

- A temporally continuous detection of the at least one beam parameter and its temporal stability are provided.

48. The method according to any one of claims 45 to 47, with the step

- Calculation of a beam propagation, in particular by means of a wavefront analysis.

49. The method according to claim 48, comprising the step

- Calculation of a focus position of the radiation field (1).

50. The method according to any one of claims 32 to 49, wherein

- The field density of the scattered radiation (3) is reconstructed taking into account particles in the medium, which would lead to artefacts of the reconstructed field density without this consideration.

51. The method according to claim 50, wherein

- A series image recording is provided, which includes several images in sequence, and Artifact-prone scattering events resulting from particles in the medium are eliminated by analysis of the serial image acquisition.

52. The method according to any one of claims 32 to 51, with the step

- Providing the medium (2) in the radiation field measuring device in a particle-free state.

53. The method according to any one of claims 32 to 52, with the step

- Detection of a volumetric particle distribution in the radiation field (1).

54. The method according to any one of claims 32 to 52, comprising the steps

- Monitoring and / or control of a radiation source with which the radiation field (1) is generated.

55. The method according to claim 54, wherein

- The radiation source is used in laser-assisted material processing in cutting and joining techniques or manufacturing in semiconductor technology or therapy and / or surgery by means of laser radiation.

56. The method according to any one of claims 54 to 55, wherein

- The radiation source includes an adjusting device, with the beam parameters of the radiation field (1) are variable, wherein

- The adjusting device in response to an intensity profile of the radiation field (1) along the longitudinal direction (z), in particular in the focus of the radiation field (1) is controlled.

57. The method according to any one of claims 54 to 56, wherein

- The radiation source includes a focusing device, and

- The focusing device is controlled in dependence on the position of the focus along the longitudinal direction (z).