WO2013011008A1

WO2013011008A1 - Device and method for generating a homogeneously illuminated surface

Info

Publication number: WO2013011008A1
Application number: PCT/EP2012/063961
Authority: WO
Inventors: Jörn Suthues
Original assignee: Wavelabs Solar Metrology Systems Gmbh
Priority date: 2011-07-21
Filing date: 2012-07-17
Publication date: 2013-01-24
Also published as: DE102011052046A1

Abstract

The invention relates to a device (10, 32, 36, 40) for generating a homogeneously illuminated surface (12), said device comprising a radiation source (14) for generating radiation (16), a matrix (18, 34), onto which the radiation (16) is projected, a measuring device (24, 38) for measuring the intensity distribution of the radiation across the surface (12), an evaluation unit (26) for determining inhomogeneities in the intensity distribution of the radiation (16) across the surface (12), and a control unit (28) for controlling and adapting the matrix (18, 34) if the inhomogeneities exceed a pre-defined threshold value.

Description

DEVICE AND METHOD FOR GENERATING A HOMOGENEOUS LIGHT AREA

The present invention relates to a device for generating a homogeneously illuminated surface, comprising a radiation source for generating a radiation and a matrix on which the radiation is projected. It also relates to a corresponding method wherein radiation generated by a radiation source is projected onto a matrix.

Such devices and methods are well known. They are used, for example, for the measurement of solar cells. From DE 10 2005 063 373 A1 is a

Solar simulator known, which allows an accurate simulation of solar spectra. The solar simulator comprises a radiation source with sufficient specific radiation, an allochromator with spectral template, a measuring space for the solar cell to be measured, an electronic measuring device, and one or more movable mirrors arranged side by side, wherein the position of the mirror depending on location in the further exploited the required disperse radiation fraction Beam path reflected. With this solar simulator, a spectral irradiance is adjusted so that it corresponds to a reference spectrum, in particular the solar spectrum. At the same time, a spectral sensitivity of an irradiated solar cell can be measured, e.g. with one or more pn junctions.

Due to the known devices, inhomogeneities on an illuminated surface can only be remedied to a limited extent since, e.g. by aging the light source the

Radiation characteristic changes continuously.

It is an object of the present invention to provide a device and a method with which a surface can be permanently illuminated in a simple manner.

This object is achieved by a device according to claim 1. Thereafter, in a device for generating a homogeneously illuminated surface, comprising a radiation source for generating radiation and a matrix onto which the radiation is projected, the following means are provided: a measuring device for measuring a Intensity distribution of the radiation on the surface, an evaluation unit for determining inhomogeneities in the intensity distribution of the radiation on the surface, and a

Control unit for driving and adjusting the matrix if the inhomogeneities exceed a predetermined threshold.

The intensity distribution of the radiation denotes the distribution of the light intensity on the surface, i. It indicates how many photons per unit of time hit which area of the surface. An advantage of the invention is that the homogeneity of the illumination on the

Surface is not dependent on a change in the device, e.g. aging or replacement of the radiation source, which continuously changes the radiation pattern, and that long radiation paths, lens arrays or optical filters which can correct the divergence of the radiation and the resulting inhomogeneities of the radiation on a surface are not required. Thus, the illumination in the device according to the invention can also be optimized over a longer period of time, so that the radiation homogeneity over the illuminated surface is constant for as long as possible. The device is therefore optimal for the measurement of solar cells, e.g. For

Photovoltaic or solar thermal, suitable. It can also be used wherever homogeneous lighting is required according to a standard, e.g. in photography or medical engineering.

The device is preferably suitable for monitoring the quality of solar cells, wherein the solar cell represents the illuminated surface. In the quality testing of solar cells, the measurement accuracy can be increased with high homogeneity of the radiation. Another advantage of the invention is that any free forms can be illuminated, i. it can be e.g. to simulate real conditions in connection with the solar cell measurement, such as a shading of the solar cell by a resting sheet.

The matrix may preferably comprise a plurality of independently controllable elements whose reflection and / or transmission properties are adjustable. Thus, the individual elements can either completely reflect or transmit the radiation of the light source, but also only partially reflect or transmit. One speaks in this connection also of the fact that the individual elements are switched on, be switched off or dimmed, depending on how the radiation from the

Reflect radiation source.

The matrix can be for example a mirror array or a liquid crystal display matrix (also called LCD (Liquid Crystal Display) matrix). The mirror array is preferably used when the radiation from matrix is to be reflected onto the surface.

If the matrix is continuously adaptable during operation, it may open

Inhomogeneities in the intensity distribution are promptly reacted. Such inhomogeneities arising during operation can be attributed, for example, to aging of the

Be attributable to light source, which can be considered in this way. Furthermore, if necessary, only certain subregions of any shape can be homogeneous

be lit up. Optionally, a semi-transparent mirror for coupling out the radiation may be provided for continuous measurement of the inhomogeneities during operation. As a result, the intensity distribution of the radiation is not measured directly on the illuminated surface, but on a reference surface. Thus, inhomogeneities of the

Radiation intensity, e.g. due to altered power of the radiation source, even during operation, e.g. when testing solar cells, measured in parallel and the matrix adjusted accordingly, without the operation being disturbed. Additionally or alternatively, at predetermined time intervals, a white area may be used to control the homogeneity between the illumination of two areas, e.g. illuminated two solar cells and these are measured.

The radiation spectrum of the radiation source preferably corresponds to the solar spectrum. Such a radiation source can be, for example, a white light source with a spectral filter wheel, wherein a spectrum can be generated by rotation of the filter wheel, which corresponds to the solar spectrum.

Optionally, the measuring device may be designed to continuously measure a power of the radiation source and the control unit to readjust the power. In this way, the inhomogeneities in the intensity distribution, in addition to matching over the matrix, can also be corrected by changing the power of the radiation source. This is particularly advantageous when the radiation source ages and up-regulated must become. In addition, a spectral distribution of the radiation on the surface could also be measured with the measuring device, for example, integrally or randomly or spatially resolved. If necessary, then an adaptation of the radiation, for example by adjusting the filter rotation, be made so that the solar spectrum is achieved.

In preferred embodiments, the measuring device has an intensity-calibrated spectrometer and / or a separate photodiode in order to be able to determine the power of the radiation source via the intensity of the radiation generated. This can be done selectively or continuously. In the case of the photodiode is used to a photodiode whose dependence of the current-voltage characteristic of the irradiated intensity is known. In conjunction with a control unit for readjusting the power of the radiation source, in particular the intensity-calibrated spectrometer allows the correction of the intensity of individual spectral ranges. The measuring device may be a single movable photodiode or a plurality, e.g. comprise photodiodes arranged in rows. For example, a can also

one-dimensional line detector can be provided, in which a single row

side by side arranged photodiodes the surface shaved line by line. Preferably, the measuring device is designed as a two-dimensional matrix detector which can detect the entire surface to be measured or only a part thereof, and then moved across the surface in an arbitrary, predetermined manner for measuring the intensity distribution. The measuring device may i.a. be designed as a CCD or CMOS detector, e.g. designed as a camera with which the surface can be displayed homogeneously. A digital resolution of such a CCD detector or CMOS detector or a digital camera with such a CCD detector or CMOS detector in which the surface can be displayed homogeneously is advantageously e.g. between 0.5 and 1 megapixel.

Preferably, the predetermined threshold for inhomogeneity is ± 5%, more preferably ± 2%, of a setpoint. The setpoint is generally determined by a standard which is e.g. used for testing solar cells (IEC 60904-9)

specified.

The object is also achieved by a method for generating a homogeneously illuminated surface, wherein radiation generated by a radiation source is projected onto a matrix. It is provided that with a measuring device a Intensity distribution of the radiation incident on the surface of the matrix is measured that inhomogeneities in the intensity distribution are determined with an evaluation unit, and that the matrix is controlled and adjusted by a control unit, when the inhomogeneities exceed a predetermined threshold.

The advantage of the method according to the invention over known methods is that the ranges in which the intensity is lower or higher than desired can be determined by the evaluation of the intensity distribution of the radiation, and a direct adaptation of the intensity to this area is carried out by targeted control of the matrix can be. In this way, the process is independent of aging of certain components of the system, e.g. the radiation source, since the adjustments based on the intensity distributions measured on the surface

be performed. In a preferred embodiment, the intensity of the generated radiation is measured, from the measured intensity the power of the radiation source is determined, which is compared with a desired value, and the power of the radiation source is regulated such that the difference between the determined power and the desired value becomes smaller. The power is preferably adjusted in such a way that the deviation from the intensity setpoint approaches zero as quickly as possible or, as far as possible, at the next repetition of the intensity measurement.

Preferably, an intensity minimum is determined from the radiation distribution and there is a local deviation of the radiation intensity on the surface of the

Intensity minimum calculated in the evaluation and to determine a

Actuator signal to the matrix used. From the local deviation it can be deduced how the matrix has to be adapted, e.g. by changing the reflectance or transmittance. Thus, the respective matrix elements which illuminate regions on the surface in which there is a greater deviation between the intensity minimum and the local intensity can be dimmed. The matrix is preferably adjusted so that the local deviation to the intensity minimum is at most 5%, preferably at most 2%.

The intensity minimum is preferably compared with a desired value for the intensity and the power of the radiation source for increasing the total radiation intensity is increased when the intensity minimum is below the desired value. In this way, the Adjust radiation intensity on the surface to a value that can be used to obtain representative test results.

Optionally, a defocussing lens may be placed between the matrix and the surface. The correction function, which additionally takes into account the defocusing effect, may optionally be adjusted to calculate which matrix element is to be changed as to obtain the desired local intensity in the illuminated area.

If individual elements of the matrix are used separately to adjust their reflection and

Transmission properties can be controlled, can be accurately determined from the local deviation, which element must be controlled to adjust the radiation intensity by changing the reflection or transmittance.

Preferably, the matrix and / or the power of the radiation source are continuously adjusted during operation in order to achieve a stable as possible homogeneity.

Advantageously, to measure the intensity distribution, the radiation is coupled out with a semitransparent mirror so that the measurement is not homogeneous

Illuminating a surface affected.

The present invention will be explained in more detail with reference to a preferred embodiment. Show this

Figure 1 is a schematic representation of a device according to

Embodiment of the invention in transmission;

Figure 2 is a schematic representation of a device according to

Embodiment of the invention in reflection; Figure 3 is a schematic representation of a device according to

Another embodiment of the invention in reflection

Figure 4 is a schematic representation of a device according to a third

Embodiment of the invention in reflection; Figure 5 is a schematic representation of the method according to a first embodiment of the invention;

Figure 6 is a schematic representation of the method according to a second

Embodiment of the invention; and

Figure 7 is a schematic representation of the method according to a third

Embodiment of the invention. 1 is a schematic representation of a device 10 for generating a homogeneously illuminated surface 12, for example a solar cell or a

Calibration area, shown according to an embodiment of the invention. The device comprises a radiation source 14 for generating a radiation 16, which is shown here simplified by a beam path. Furthermore, the device 10 comprises a matrix 18 onto which the radiation 16 is projected. Between the radiation source 14 and the matrix 18, an optical system 20 for focusing the radiation 16 on the matrix 18 is arranged. In a beam path of the radiation 16 transmitted through the matrix 18, a further optical system 22 is initially arranged, which images the radiation 16 transmitted through the matrix 18 onto the surface 12 provided for illumination.

On the surface 12, in the example shown here, a measuring device 24, e.g. a CCD sensor or a single movable photodiode connected to one

Intensity distribution of the impacted on the surface 12 radiation 16 is measured. The measurements are sent to an evaluation unit, e.g. a computer 26, which determines inhomogeneities in the intensity distribution of the radiation 16 on the surface 12. A control unit 28 is connected to the computer 26 and controls the matrix 18 with a corresponding drive signal, so that on the basis of the determined inhomogeneities an adaptation of the matrix 18 is made when the

Inhomogeneities exceed a predetermined threshold. The control unit 28 may also be designed as part of the computer 26. The measuring device 24 can also measure a power of the radiation source 14 and evaluate it with the computer 26 so that optionally, for example in the case of inhomogeneities which are additionally influenced by aging of the radiation source 14, an adaptation of the power of the radiation source 14 via a second control unit 30 can be. The control units 28, 30 may also be a single device, which both the matrix 18 and the radiation source 14 drives. To the performance of

Radiation source 14 to measure the measuring device 24, for example, a

Have photodiode whose dependence of the current / voltage characteristic of the irradiated radiation intensity is known, or an intensity-calibrated

Spectrometer. Depending on the measured intensity, the one

Radiation source power corresponds, and their deviation from a desired intensity value or equivalent target power value, the power of the radiation source 14 can be readjusted via the control unit 30 such that the deviation from the desired value is as low as possible.

In the embodiment considered in FIG. 1, the matrix 18 is an LCD matrix which consists of segments which can independently change their brightness. For this, the segments are irradiated with unpolarized light and hit one

Polarizing filter that polarizes the radiation. With electrical voltage in each segment, an alignment of the liquid crystals is controlled to hit the polarized light. This makes it possible to change the transmissivity for the polarized light.

For example, a mirror array, e.g. A "Digital Micromirror Device" (DMD) Each micromirror of such a mirror array can be individually adjusted in its angle and usually has two stable end states, between which it can change up to 5000 times within one second The resolution of the projected image, where a mirror can represent one or more pixels The DMD can be located in a Digital Light Processing (DLP) projector.

The matrix 18 may also be used as an optical switch to, for example, etch the radiation source 14 in steady light but to illuminate the area 12 only for a certain time interval, eg 10 ms. Furthermore, by adapting the matrix 18, an arbitrary shape can be generated on the surface 12. That is, it is not necessary to illuminate the entire surface 12, but it is also possible to illuminate a part of the surface 12, and this illuminated part can take any shape, such as circle, rectangle, oval or any other shapes. It can also be two, three or more areas of any Form be lit at the same time. This is achieved by switching on or off individual matrix elements.

For the testing of solar cells is preferably a radiation source 14, the spectral range of which is as similar as possible to the sun. The spectrum should be the

Standard spectrum AM1, 5 adapted and have a radiation power of 1000 W / m ² . A coupling of the radiation source 14 can also be carried out by a light guide or mixing rod, for example made of glass fiber, and be projected by this onto the matrix 18. In this case, a prism arrangement is conceivable, is combined with the differently colored radiation to form a beam before it enters the mixing rod. Other optical elements which may alternatively or additionally be arranged in the beam path are, for example, mirrors and filters.

FIGS. 2, 3 and 4 show further exemplary embodiments of the device according to the invention. For each corresponding components, the same reference numerals have been used.

In Figure 2 is a corresponding to Figure 1 device 32 according to a

Embodiment of the invention shown, in which case a matrix 34 is used, which reflects the radiation on the surface 12 instead of transmitting. For example, the above-mentioned mirror array can be used for such a matrix 34.

Figure 3 shows another example of a device 36 according to the invention, in which the measuring device comprises a CCD detector 38, e.g. is designed as a digital camera, which detects the radiation on the surface 12 homogeneous. The image of the CCD detector 38 is evaluated to determine the inhomogeneities in the computer 26, which then controls the matrix 34 for adaptation via the control unit 28. The

Control units 28, 30 are formed as part of the computer 26. As in Figure 2, this device 36 is constructed in reflection, an alternative embodiment in transmission would also be conceivable. The CCD detector 38 preferably has a digital one

Resolution between 0.5 and 1 megapixel around the surface 12 to represent homogeneous. With such resolving power, it is achieved that the inhomogeneities of the radiation intensity are not more than ± 2% of a target value. The setpoint is usually given in a standard, for quality measurements on solar cells this is the standard IEC 60904-9. According to the present invention should significantly lower Inhomogeneities are achieved so that the setpoint can be met much more accurately.

In Figure 4, a further device 40 is shown as an embodiment of the invention, in which between the radiation source 14, which in this embodiment as

White light source is formed, and the matrix 34 in addition to the optics 20 is still a filter wheel 42 is arranged. This filter wheel 42 allows rotation of a generation of any spectrum, which then hits the matrix 34. Preferably, spectra are generated which correspond as closely as possible to the solar spectrum. The filter wheel 42 may have, for example, a wavelength range of 300 nm to 1200 nm. A rotational frequency of the filter wheel 42 must be a multiple of a response time of a solar cell when such is used as the surface 12 to be illuminated.

In general, inhomogeneities of the radiation intensity on the surface 12 can be adjusted by measuring the surface 12 once over the matrix 18, 34. The

However, device 40 in Figure 4 is particularly suitable for making continuous measurements of the radiation intensity. For this purpose, the device 40 in FIG. 4 comprises a semitransparent mirror 44 which lies in the beam path between the matrix 34 and the illuminated surface 12. With the help of this mirror 44, the radiation

coupled and may be connected to a measuring device, e.g. the CCD detector 38, are measured. The homogeneity distribution of the radiation on the mirror 44 corresponds to the homogeneity distribution on the illuminated surface 12 and can therefore serve as a reference for driving the individual matrix elements in order to respectively vary the radiation intensity and to set the desired radiation intensity. The power of the radiation source 14 can also be detected by the measuring device 38, for example with the aid of an intensity-calibrated photodiode or an intensity-calibrated one

Spectrometer, and depending on the values measured on the mirror 44, e.g. also in combination with the matrix 18, 34, adapted to change the radiation intensity, also continuously. In this way, inhomogeneities of the radiation may also occur during operation and without the operation, e.g. Quality measurements

Solar cells to disturb to be measured and the matrix 34 and, where appropriate, the power of the radiation source 14 are continuously adjusted. Also, this device 40 is arranged in reflection, but is also suitable for a construction in transmission. The measuring device 24, 38 can also be designed such that they are sampled and / or spatially resolved and / or continuously during operation the spectral

Distribution of the radiation 16 measures so that it is also possible, e.g. by feedback to the control unit 30 of the radiation source 14 to make changes to the radiation source 14 with respect to the spectral distribution.

Furthermore, in certain embodiments, the measuring device 24, 38 may be designed such that it detects a total intensity of the radiation 16 on the surface 12. FIG. 5 shows a schematic representation of a first embodiment 46 of FIG

Method for generating the homogeneously illuminated surface. In a first step 48, the intensity distribution of the radiation impinging on a surface from the matrix 18, 34 is measured with the measuring device 24, 38. In a second step 50, the absolute intensity minimum is determined from the intensity distribution. In a third step 52, the local deviation of the intensity distribution from the intensity minimum is determined for at least one surface area. Areas where the local deviation is greater than a setpoint, e.g. 2% of the intensity minimum, is shaded, i. in a fourth step 54, the matrix is adjusted so that the corresponding areas are less heavily illuminated, e.g. by changing an angle of the individual mirrors of a mirror array or by changing the orientation of the liquid crystals in individual

Segments of an LCD matrix.

Alternatively or additionally, the intensity minimum can also be determined and the total radiation intensity can then be increased until the intensity minimum reaches a predetermined value, e.g. 1000 W, is set. Then, an intensity maximum can be attenuated until the inhomogeneity of the radiation intensity is at most 5%, preferably at a maximum of 2%.

FIG. 6 schematically shows a further embodiment 56 of the method for generating the homogeneously illuminated surface. The first two steps correspond to the embodiment shown in FIG. In a third step 58, the absolute intensity minimum is compared with a target value for the radiation intensity on the surface. If the intensity minimum undershoots this setpoint value, the power of the radiation source is increased in a fourth step 60, so that the overall radiation intensity on the surface is higher by a predetermined value. After that, in one fifth step 62 determines the local deviation of the intensity distribution from the intensity minimum increased by the predetermined value. For areas in which the local deviation is greater than a target value, for example 2% of the intensity minimum, the matrix is adjusted accordingly in a sixth step 64, so that the corresponding areas are less strongly illuminated, for example by changing an angle of the individual mirrors a mirror array or by changing the orientation of the

Liquid crystals in individual segments of an LCD matrix. Also, by quickly turning on and off individual mirrors of a mirror array or individual segments of an LCD matrix, e.g. in 0.2 ms cycle the intensity of the radiation on the surface can be damped. In general, one can assume that the whole

In the fourth step 60 of the method 56 according to FIG. 6, the intensity distribution shifts upwards by a predetermined value when the power source of the radiation source is increased, so that the step 62 can also be performed before the steps 58, 60. It may be useful to increase the accuracy in the adjustment of homogeneity to measure the intensity distribution again before determining the local deviations (step 62). A further increase in accuracy can be achieved if the intensity minimum is subsequently also redetermined.

In a further embodiment, which is illustrated in FIG. 7, after measuring the intensity distribution on the illuminated area (step 48), the power of the radiation source is determined from one or more intensity values (step 68). This is compared with a desired value (step 70) and, if appropriate, the power of the radiation source adapted (step 72) to reach the desired power and the matrix adapted (step 64) to correct the intensity distribution if necessary. Is the power by means of a

determined intensity-calibrated spectrometer, powers for different spectral ranges can be determined and compared with separate setpoints. With appropriately designed radiation sources, individual spectral ranges can also be readjusted separately with respect to their power. With the method described in Figures 5, 6 and 7 thus a homogeneous illumination of a surface can be achieved. In this case, the aging of the light source can be compensated by feedback if necessary. Also, any free forms can be illuminated, which need not necessarily be geometric, but also can emulate, for example, actually occurring in nature shading, as they regularly occur during operation of solar cells, eg by striking foliage. It also can if necessary Different gradations of shading or lighting can be realized, for example, gray levels are generated.

Claims

claims

1. Device (10, 32, 36, 40) for generating a homogeneously illuminated surface (12) comprising

- A radiation source (14) for generating a radiation (16), and

a matrix (18, 34) onto which the radiation (16) is projected,

marked by

a measuring device (24, 38) for measuring an intensity distribution of the radiation (16) on the surface (12),

an evaluation unit (26) for determining inhomogeneities in the

Intensity distribution of the radiation (16) on the surface (12), and

- A control unit (28) for driving and adjusting the matrix (18, 34) when the inhomogeneities exceed a predetermined threshold.

2. Device (10, 32, 36, 40) according to claim 1,

wherein the matrix (18, 34) comprises a plurality of independently controllable elements whose reflection and / or transmission properties are adjustable.

3. Device (10, 32, 36, 40) according to claim 2,

wherein the matrix (18, 34) is a mirror array or an LCD matrix.

4. Device (10, 32, 36, 40) according to one of claims 1 to 3,

wherein the matrix (18, 34) is continuously adaptable during operation.

5. Device (10, 32, 36, 40) according to one of claims 1 to 4

with a semi-transparent mirror (44) for coupling out the radiation (16) for a continuous measurement of the inhomogeneities during operation.

6. Device (10, 32, 36, 40) according to one of claims 1 to 5,

wherein a radiation spectrum of the radiation source (14) corresponds to the solar spectrum.

7. Device (10, 32, 36, 40) according to one of claims 1 to 6, wherein the measuring device (24, 38) is designed to continuously measure a power of the radiation source and the control unit (28, 30) to readjust the power.

8. Device (10, 32, 36, 40) according to one of claims 1 to 7, wherein the

Measuring device (24, 38) has an intensity-calibrated spectrometer.

9. Device (10, 32, 36, 40) according to any one of claims 1 to 8, wherein the

Measuring device (24, 38) comprises a photodiode.

10. Device (10, 32, 36, 40) according to one of claims 1 to 9,

wherein the measuring device (24, 38) is a two-dimensional matrix detector.

1 1. Device (10, 32, 36, 40) according to one of claims 1 to 10,

wherein a predetermined inhomogeneity threshold is ± 5%, preferably ± 2%, of a set point.

12. Method (46, 54, 62) for generating a homogeneously illuminated surface (12), wherein radiation (16) generated by a radiation source (14) is projected onto a matrix (18, 34), characterized

an intensity distribution of the radiation (16) impinging on the surface (12) from the matrix (18, 34) is measured with a measuring device (24, 38),

in that with an evaluation unit (26) inhomogeneities in the intensity distribution are determined, and

the matrix (18, 34) is controlled and adapted via a control unit (28) if the inhomogeneities exceed a predetermined threshold value.

The method (46, 54, 62) of claim 12, wherein the intensity of the generated

Radiation (16) is measured, from the measured intensity the power of

Radiation source (14) is compared, which is compared with a target value, and the

Power of the radiation source (14) is controlled so that the difference between the determined power and setpoint is lower.

14. Method (46, 54, 62) according to claim 12 or 13,

wherein an absolute minimum intensity is determined from the radiation distribution and wherein a local deviation of the radiation intensity on the surface (12) of the Intensity minimum calculated in the evaluation unit (26) and used to determine a drive signal to the matrix (18, 34).

15. The method (46, 54, 62) according to claim 14,

wherein the intensity minimum is compared with a setpoint for the intensity and wherein a power of the radiation source (14) to increase the total

Radiation intensity is increased when the intensity minimum is below the setpoint.

16. The method (46, 54, 62) according to any one of claims 12 to 15,

wherein individual elements of the matrix (18, 34) are driven separately to adjust their reflection and transmission characteristics.

17. The method (46, 54, 62) according to any one of claims 12 to 16,

wherein the matrix (18, 34) and / or the power of the radiation source is continuously adjusted during operation.

18. The method (46, 54, 62) according to any one of claims 12 to 17,

wherein the radiation (16) for measuring the intensity distribution with a

semitransparent mirror (44) is decoupled.