WO2008067938A1 - Method for measuring birefringence and/or retardation, in particular on at least partially transparent films, and associated apparatus - Google Patents

Abstract

An improved method and an improved apparatus for measuring birefringence and/or retardation on samples (3) are distinguished, inter alia, by the following measures: with a radiation arrangement having at least one light source (LQ1, LQ2) or having at least two light sources (LQ1, LQ2) for generating two light beams (LS1, LS2; LS1_1, LS1_2; LS2_1, LS2_2) - provision is made of a polarization-maintaining diffractive element (DO; DO1, DO2) and a detector device (9; 9a, 9b) with polarization-sensitive analysers (A; A1, A2; 19), which can be used to measure the intensity of the diffraction structure sample (BM) generated by the component beams.

Description

Method for measuring the birefringence and / or the retardation, in particular on at least partially transparent films and associated apparatus

The invention relates to a method for measuring the birefringence and / or the retardation, in particular at least partially transparent films according to the preamble of claim 1 and an associated apparatus according to the preamble of claim 27.

A corresponding measuring method or a corresponding device is primarily used for the fast interference-insensitive real-time measurement of samples by means of electromagnetic radiation, i. in particular radiation in the visible range.

The field of application of the invention is therefore not limited. One of the possible applications preferred in the context of the present invention relates to the online measurement (real-time measurement) of the double-billing or the retardation of transparent or at least partially transparent, ie optical plastic films and films during the production process. With such a measuring method or with such a measuring device, a quality or process control, for example in the production of plastic films, can be carried out online. The measured values are used to calibrate specific film properties and process settings. As a result, the costs can be saved by complex offline measurements or misalignments. As a result of the measurement, it is also possible to measure important quality features online, ie in real time, above all in the visible wavelength range, as well as other properties such as transmission, for example on transparent films.

A partial aspect of the device is u.a. in that during the production process, the film properties can be adjusted in a targeted manner by changing the process and in particular the stretching parameters by means of the measured birefringence properties. For example, the retardation properties of e.g. optical films are adjusted by changing the stretching parameters targeted. Thus, the final film property can be adjusted during the production process. The same applies to the adjustment of the process parameters and final film properties, e.g. for shrink films or the minimization of the so-called bowing behavior u.a.

A corresponding film thickness measurement in the online or real-time method, which can take place externally but can also be an integral part of the claimed measuring device, thus serves to calculate the birefringence values.

"Birefringence" in electromagnetic waves, ie particular in the visible range of light rays, means that a polarized light beam is split into two components and passes through the medium to be examined at different speeds through the film. The birefringence is a value inherent to the material of the sample under investigation or its inherent size, which allows conclusions to be drawn about the material properties of the sample to be investigated. It is often spoken of "retardation". The two normal and extraordinary beam polarization components pass through the sample to be examined (for example, the film to be examined) at a different speed, namely along a so-called "fast axis" and a so-called "slow axis", which according to the " slow axis "extending polarized light beam quasi" delayed "passes through the sample to be examined, so here is experiencing a" retardation ". The magnitude of the "retardation" is a measure of length, usually in the nanometer range "nm".

Therefore, the term "retardation" is often used and understood as an equivalent term to "birefringence", since the retardation corresponds to the birefringence value multiplied by the thickness of the specimen.

The measurement of the retardation or birefringence is usually based on the so-called "Senarmont method", in which the phase angle of the polarized light beams is obtained by time-resolved rotation of one of the polarization components. These methods require at least one rotation by a value π of a polarization component and are therefore for on-line or real-time measurement -A -

fast running films not suitable.

In addition, already modified Senarmont methods have been developed and proposed in which the polarization optics; be replaced by fast-rotating electro- or mechanical-optical elements, so as to enable a timely measurement of retardation or birefringence. Such processes have become known, for example, from WO 99/42796 A1 and within the scope of a further development based thereon from WO 03/040671 A1.

However, a disadvantage of these methods is that they require a very high computing power and, because of the clock rates of the measured value acquisition, can almost only detect a "smeared" or "integrated" average value over a certain distance of the film in the case of high-speed films, ie no real-time Allow resolution of sufficient magnitude.

In particular, in uniaxially and biaxially stretched films also usually higher orders occur (R> λ), which can not be measured with the usual Senarmont method. Examples in the literature are known in which higher orders can be determined by means of two closely spaced wavelengths and a minimization method.

It has been shown that in particular with optical of foils all three refractive indices n _x, n _γ, n _z and the birefringence values .DELTA.n _{xy, x2} .DELTA.n or .DELTA.n _yz for quality control are required. The refractive index is known to be the refraction of the electromagnetic wave in The sample to be examined (film), ie the change in direction of the wave due to a local change in its propagation velocity, which is sometimes referred to as "refractive index", which is important in all three spatial axes.

Here it is necessary to distinguish it from the actual measuring method, in which the birefringence measured values are determined, and not at first the refractive indices.

For example, US Pat. No. 5,864,403 A for measuring the absolute biaxial refraction values of a plastic material proposes using a white light source with a different wave spectrum, by means of which two light beams are irradiated onto a sample which passes through the sample at the same position both light beams are aligned at a different angle to each other. The beams first pass through polarizers before they hit the sample at the same point. After passing through the sample, the beams strike another polarizer before hitting a detector after wavelength separation by a spectrograph to measure the beam intensity as a function of wavelength for the angles of incidence of the two beams at different times. From this, the birefringence value or the retardation is ultimately determined. From the knowledge of the thickness of the film, the in-plane value and the out-of-plane value (IP OP value) for the wavelength range should then be calculated according to this prior publication.

One way of estimating the retardation or birefringence values online (ie in real time) for fast-moving for- To measure the railway, is to convert the time-resolved signal from the rotating polarization component in a spatially separated polarization information. In this case, a polarization-maintaining diffractive optical element (ie a diffraction structure) is used to image the rotation of a polarization element into a spatially distributed pattern. Each of these pattern areas is then assigned a single analyzer and a detection unit, wherein the individual analyzers are arranged with respect to their polarization plane in different directions to each other, as can be seen from the prior publication DE 195 37 706 Al. In this case, the light beam to be analyzed is multiplied by means of a synthetically generated two-dimensional diffraction structure in a large number of sub-beams same beam profile and the same intensity, the plurality of beams then a corresponding number of linearpolari- sationsempfindlichen elements with different angular directions through, then to a ent - Meet a number of detectors whose signals can be Fourieranalysiert with respect to the angle.

In contrast, the object of the present invention is to provide an improved measuring method and an improved apparatus for a real-time birefringence measurement, with which the values that are to be examined are as accurate as possible on-line (that is, in the real-time method) with comparatively little equipment complexity and high resolution Sample, in particular with respect to fast moving foil webs can be determined.

The object is achieved with respect to the method according to the claim 1 and with respect to the device accordingly solved the features specified in claim 27.

Advantageous embodiments of the invention are specified in the subclaims.

By means of the method according to the invention and the associated measuring device, the quality and, above all, the process control, for example in the production of plastic films and films, which are transparent or partially transparent, can be improved in real time, ie online. The measured values obtained can be used for the calibration of specific film properties and for process engineering settings. Thus, the costs are saved by complex online measurements and mishaps. Finally, within the scope of the invention, it is also possible to measure important quality features from the visible wavelength range and thus further properties with respect to the samples, especially in the case of transparent or partially transparent plastic films. An example of process control here is the targeted influencing of the final film properties by means of the measurement of birefringence (DB) values.

Above all, within the scope of the invention, the retardation and the birefringence values can be determined on rapidly moving plastic film webs, which are moved, for example, at a speed of up to 600 m / min. The following results can be determined within the scope of the invention:

a) It is possible to determine the values for the retardation and the birefringence values with respect to the samples of zeroth and higher orders to be examined; b) it is possible to determine the retardation and birefringence values in all three spatial directions;

c) it is possible to determine the wavelength dependence with respect to the retardation and birefringence values;

d) the wavelength-dependent transmission can be determined;

e) in the detection over several wavelengths or wavelength ranges, together with the determination of the transmission via the Lambert-Beersche law, the thickness of the sample (film) can be determined, which can then be used to determine the birefringence values; and

f) the refractive values can be determined.

Particularly in the case of optical films, a decisive quality criterion is the ratio of the refractive values to one another. A distinction is made with respect to the birefringence values (n _x -n _γ), which lie in the film plane, and as so-called. In-plane refractive values are referred to (n _x -n _γ), wherein below the term "in-plane" in some cases abbreviated as "IP". In addition, the corresponding refractive values exist in the thickness direction of the test sample, that is, for example, in thickness direction of the to be investigated film which briefly as out-of-plane birefringence values (n _z -n _x), (n _z -n _γ) denotes advertising the , where the term "out-of-plane" is abbreviated hereafter also abbreviated as "OP". Since these are optical films, of course, the birefringence values in the visible range (from, for example, 400 to 700 nm) of particular interest.

As a rule, the so-called out-of-plane birefringence values are greater than the in-plane birefringence values. It should also be noted that the optical films are usually only zeroth or first order (R <λ, R <2λ) is used. When designing a universal birefringence measuring device, the wavelength dependence over the visible range must also be taken into account.

In uniaxial as well as in biaxially stretched films, birefringence values of higher order generally occur which can not be determined with standard measuring devices. In the case of these devices, order leaps occur which nullify a clear interpretation of the measurement.

A remedy here can only be provided by superimposing at least a second measuring beam with a slightly different wavelength collinearly with the main beam. Due to the resulting path differences at different wavelengths, the order of the birefringent foil can then be deduced with the aid of a minimization procedure. For example, e.g. Also, the measurement of previously unclear determinable high-stretched polypropylene films (PP films) possible.

In particular, when a broad spectral range is to be measured, it has also proved to be favorable in the context of the invention not only to carry out the corresponding order determination with, for example, two discrete wavelengths having a wavelength offset Δλ to one another, but a measurement based on To perform a multi-wavelength method in which more than two wavelengths are used for the measurement simultaneously. The order determination is possible for the IP and OP beam path.

These and other advantages of the invention will become apparent from the following explained in more detail with reference to drawings embodiments. In detail:

FIG. 1 shows a schematic arrangement of a measuring device according to the invention for carrying out the measuring method according to the invention;

FIG. 2 shows a first embodiment variant for illustrating a possible beam coupling for the in-plane and the out-of-plane excitation;

FIG. 3 shows an embodiment deviating from FIG. 2 according to a second variant for in-plane and out-of-plane excitation, in particular for optical films;

FIG. 4 a schematic representation of a detection unit for detecting the incident light beam with respect to the in-plane or the out-of-plane light beam evaluation;

FIG. 5 is an illustration of the light beam split into a plurality of partial beams to produce a different one Intensity distribution after passing through a polarization-dependent analyzer configuration according to a prior art embodiment;

FIG. 6 shows a corresponding illustration according to FIG. 5, however, for carrying out a measuring method according to the invention;

FIG. 7 shows a first schematic illustration of a diffraction pattern of a light beam obtained in the context of the measuring method according to the invention, after the light beam has passed through a wavelength-dependent diffractive element generating a multiplicity of partial beams;

FIG. 8 shows an exemplary embodiment, deviating from FIG. 7, of a different analyzer arrangement with a correspondingly differently obtained diffraction structure pattern; and

FIG. 9 shows a diagram for explaining the determination of the phase angle and thus the retardation of the birefringent medium in accordance with the examined sample.

In the following, reference will first be made to FIG. 1, in which a basic schematic representation of an in-plane and an out-of-plane measurement by means of two light beams is explained. For this purpose, in FIG. 1, for example, along the arrow depiction, a fast-moving transparent or at least partially transparent (optical) plastic film 3 is shown transversely to the film plane.

On the one side of the plastic film 3, in the illustrated embodiment on the left side, an arrangement with a light beam generating device 5 is shown, by means of which a first light beam LS1 and a second light beam LS2 are generated.

According to the embodiment of Figure 1, two light beam generating means 5a and 5b are provided, wherein by means of the light beam generating means 5a a falling perpendicular to the plane of the sample to be examined 3 light beam and by means of the light beam generating means 5b an angularly aligned second light beam is generated , the X (or in a closely as possible circumscribed same sample area X) at the same location in a different from 90 ° angle of, for example, α _op incident on the plane of the sample 3, wherein the angle α _0P smaller than the polarization reflection angle, Thus, preferably less than 50 °, in particular 30 °.

Each of the two light beams LS1 and LS2 is generated by means of a light source LQ1 and LQ2, which may for example consist of a white light source such as a lamp or one or more lasers with fixed or tunable wavelengths.

The light beam thus generated is passed through a wavelength separator WS1 or WS2; this can be a monochromator, an edge filter or an acoustically optically transparent be tuneable filter (AOTF). The wavelength separators are necessary if:

a) only over a certain wavelength range or only with certain wavelengths to be measured,

b) higher orders are to be determined in a two- or multi-wavelength method,

c) a calibration of the detection unit is to be carried out,

d) integrally the thickness of the sample is to be determined.

According to the embodiment of Figure 1, the light beams with respect to the in-plane and with respect to the out-of-plane branch can be optically coupled to each other. This is indicated by means of the coupler Cl or C2 in FIG.

This coupling can also be used in optical films (samples 3) with zeroth-order measurements to manage with only one light source. For this purpose, for example, the light source LQ2 and the wavelength separator WS2 omitted. The so-called second light beam in the out-of-plane branch is then supplied by the light source LQ1 and by the wavelength separator WS1 alone. After the beam coupling, which will be explained in detail later, then the respective light beam LS1 or LS2 is widened with an expander lens CU1 or CU2, in which case the respective light beam LS1 and LS2 first a polarization optics PO1 and PO2 and retardation plates (λ / 2). passes through and then radiates through the film 3. The optional optical coupling of the two light sources or light beams can serve the following purposes:

a) the determination of the retardation and thus the birefringence values of higher orders;

b) the time-synchronous detection of the in-plane and out-of-plane measured values for the film 3 of zero order;

c) the acquisition of in-plane and out-of-plane measurements for higher-order films;

d) selectively detecting certain wavelengths and ranges;

e) the reference acquisition for transmission and thickness determination; and

f) the calibration of the detection units.

If, as pointed out above, instead of two separate light sources and two wavelength separators, only one light source LQ and only one wavelength separator WS are used and the light beam is then split into two light beams LS1 and LS2, then a cost saving can also be achieved achieve the coupled use of light sources for in-plane and out-of-plane measurement.

Before discussing the further evaluation of the light beams LS1 and LS2 radiating into the film in the film region X, reference will first be made, with reference to FIG. 2, to a first variant of the beam coupling for the in-plane process. and explain the out-of-plane suggestion.

In Figure 2, the measurement setup is explained in greater detail, wherein like reference numerals refer to the same parts as in Figure 1.

To determine the retardation and birefringence values higher than the first order, at least a second wavelength is necessary (as discussed above for example with respect to the multi-wavelength method), which is collinearly irradiated by the approximately equal sample volume. In a variant of the invention, this can be done by using at least one second light beam with a wavelength offset from the first light beam or by using a light beam having a wavelength range. An analogous procedure is possible for several wavelengths.

For example, assuming that the light source LQ1 having a wavelength of 635 nm and the second light source LQ2 having a wavelength of, for example, 685 nm are collinearly irradiated in the approximately same sample area X, in practice higher orders up to the ninth order may be used the sample to be examined are determined. The closer these two aforementioned wavelengths are to one another, the higher the order to be determined theoretically. In practice, however, wavelengths still need to be separated cleanly, which is why there is often a wavelength difference

Δλ> 10 nm

necessary is. For many applications, a value of Δλ s 30 nm

meaningful. Such values can thus generally vary between 10 to 100 nm, in particular between 10 to 80 nm or 10 to 60 nm or 10 to 50 nm. As stated, values of about 20 nm to 40 nm are often suitable.

2, two light sources LQ1 and LQ2 are used, the light beams generated above each being supplied to a wavelength separator WS1 or WS2, as explained with reference to FIG.

The two light beams LS1 and LS2 generated above are coupled to one another via a beam splitter optics SK1 or SK2.

If, for example, a broadband light source with a monochromator is used, the wavelength of the light source LQ1 can be, for example

λl = 400-700 nm

pass through, while by means of the light source LQ2, for example, a wavelength range of

λ2 = (400 + Δλ) - 700 nm

is irradiated time-synchronous with constant Δλ. There is also the possibility to determine the order in so-called trial operation. Assuming that the light source LQ1 is scanned in the visible range, then the following is still to be explained. Switching devices Sl for the first light beam LSl and the switching device S2 for the second light beam LS2 the possibility to control the light source LQ2 controlled in a wavelength λl + Δλ and then to determine the order. This principle works analogously when different discrete laser sources are used instead of a broadband light source.

According to FIG. 2, it can be seen that the two light sources LQ1 and LQ2 generate light beams which, after passing through the wavelength separators WS1 and WS2 for the in-plane and out-of-plane beam path in a splitting unit SU1 and SU2 in FIG Rays with the same intensity are split unpolarized. These splitting units SU1 and SU2 can consist, for example, of one non-polarizing broadband beam splitter BS1 and BS2 and one each of a 100% mirror M1 or M2. The splitting units can also be realized by all other suitable measures, for example also in the form of an optical waveguide multiplexer.

Thus, the light beam LS1 is divided via the beam splitter BS1 into the passing light beam LS1_1 and into the light beam LS1_2 branching off from it. Likewise, the second light beam LS2 is split into the light beam LS2_1 and L2_2 via the second beam splitter BS2.

The light beam LS1_1 radiating with the wavelength X _{1 is} fed to a collimation unit CU1_1 (widening optics CU1_1) and the second part beam LS1_2 to the widening optics CU1_2, thereby widened and subsequently fed to a further beam splitter BS1_1 or BS2_1. In these beam splitters mentioned above in each case, a portion of the light beam LS1_1 or LS1_2 emitting with the wavelength X ₁ passes through the beam splitter BS1_1 or BS2_1.

The same applies to the second light beam LS2, which is split into two light beams LS2_1 and LS2_2 via the splitting unit SU2 mentioned above, the one light beam LS2_1 likewise being fed to the mentioned beam splitter BS1_1 via an expander optic CU2_1 and the second beam splitter LS2_2 to the further beam splitter BS2_1 a portion of the light beam is deflected parallel to the respective other light beam LS1_1 or LS1_2, so that both on the in-plane branch and on the out-of-plane branch portions of both light beams LS1 or LS2 spread.

These light beams then preferably run first by a delay element λ / 2 (often realized in the form of a so-called retardation plate with effecting a λ / 2 phase shift), to then the mentioned polarization optics POl or PO2 and then then the sample 3, for example in the form of a transparent To film.

In the mentioned in-plane and out-of-plane beam paths (which are also referred to as IP or OP beam paths for short), in each case the light beams with the wavelength X ₁ and λ ₂ each have half the intensity.

As is apparent from Figure 2, each of the two split light beams in the two other beam splitters BS1_1 and BS2_1 partially reflected in a 90 ° angle, so that this beam portion with Detectors DETl or DET2 can be used to determine the transmission as a reference. These measurements can also be used to determine the film thickness over the Lambert-Beersche law.

The aforementioned switches S1 and S2 (which are arranged in front of the widening optics CU1_2 and CU2_1) serve, as mentioned, for determining the order, but also for calibrating the respective retardation at different wavelengths.

Thus, by means of the embodiment according to FIGS. 1 and 2, a discrete detection of defined wavelengths or ranges is possible by means of the detection unit which will be discussed below. With discrete irradiated wavelengths A ₁ A ₂ , a corresponding calibration of the detection unit can be dispensed with.

The following is an explanation of the exemplary embodiment according to FIG. 3, which shows a variant embodiment in deviation from FIG.

In the embodiment according to FIG. 3, there is the possibility that the two light beams LS1 and LS2 comprise discrete wavelengths A ₁ and A ₂ , A ₃ ..., A _n , where n = 1, 2, 3..., N , that is, the natural numbers up to n, or it is possible that the two light beams each radiate in a wavelength range A _x . However, in this case it is then necessary to calibrate the detection unit explained below for the respective wavelength.

The embodiment according to FIG. 3 is used in particular for the simultaneous determination of the retardation values for optical films in the visible wavelength range.

In the embodiment according to FIG. 3, in which the same reference numerals and the same designations refer to the same parts, a light beam having a wavelength range X ₁ X is thus generated in the light source LQ ₁ and the following wavelength range separator WS 1 and subsequently a beam splitter unit SU with a beam splitter BSl and a mirror Ml arranged offset thereto, whereby the light beam LS1 is split into two light beams LS1_1 and LS1_2. The two beam branches produced in this way are fed to each other in-plane and out-of-plane at different angles, ie the beam is perpendicular to the film and the other at an acute angle.

As indicated in FIG. 3, a separate second light source LQ2 and a further wavelength range separator WS2 can alternatively be provided for the second beam path, which is delimited in dashed lines in FIG. In this case, the beam splitter SU would then be omitted. The above-mentioned wavelength range separator WSL thus serves to filter out a certain wavelength range in the X ₁ X from the one light source LQL generated light beam and transmitting. In the above-mentioned variant, however, two light sources LQL and LQ2 used, each having a downstream wavelength band separator WSL or WS2 may be that a certain wavelength range X ₁ X or X ₂ X produced from the in the two light sources LQL and LQ2 filter out light beams and to transmit, wherein X ₁ X ₂ X and X is the same wavelength ranges, at least overlapping wavelength ranges or can represent mutually offset wavelength ranges. The same applies to the case in which discrete wavelengths are used instead of a wavelength range.

Of course, instead of the mentioned wavelength ranges X ₁ X, discrete wavelengths X _n can also be set, as in the exemplary embodiment according to FIG.

In order to be able to calibrate the detection units to be described later with specific wavelengths, the

Wavelength separators WSl and WS2 (for light beam selection) used for calibration.

As described above, a monochromator or various edge filters can be used for calibration.

After calibration, the calibrator may be removed or continue to serve as a wavelength range selection unit. The remaining units and their functionality basically correspond to the construction according to FIG. 2, wherein in each wave the beam of light LS1_1 radiating in a wavelength range passes through a beam splitter BS1_1 or BS2_1, as well as the polarization optics, in order then to the sample to be examined, for example in shape of the movie to fall.

In the case of the two beam splitters mentioned above, in each case a portion of the respective light beam is decoupled and fed to the detector unit DET1 or DET2.

These measured quantities in the transmitting and receiving part can be used to determine the transmission and for direct determination the film thickness be used over the Lambert-Beersche law. The thickness measurement then serves to calculate the birefringence values via the phase angle or the retardation.

The detection units 9 (namely the detection unit 9a for determining the IP values and the detection unit 9b for determining the operating theater values) are explained in more detail below with reference to FIG. 4, as can already be seen from the principle of FIG. With reference to Figure 4, this structure is shown in greater detail, being preceded that the detection units as well as the light beam generating devices in the in-plane and in the out-of-plane beam path are constructed analogously, which is why with reference to Figure 4 only Detection part for the IP or the OP components is described, this detection part 9, 9a for the in-plane branch and in another embodiment as a detection part 9, 9b for the out-of-Plane branch is used (said Detection parts 9, 9a hereinafter also partially referred to as D ₁ and D ₂ ).

It is already noted at this point that to determine the IP as well as the OP values only one detection branch is necessary. Only if the result is to be achieved with a higher resolution (which will be discussed later), can further detection branches D _{N be} appropriate.

It should already be noted at this point that by means of the described detection unit, a multi-wavelength evaluation and detection can take place at the same time and that also a continuous evaluation of Determination of higher orders (to exclude dispersion errors) is also made possible.

The light beam LS either from the in-plane or the out-of-plane branch emerging from the sample and subsequently referred to briefly as LS is elliptically polarized and contains after passing through the sample 3 (in the form of the transparent or partially transparent film 3) after passing through the film 3, the required polarization information in the form of a phase angle, which can be converted into a corresponding value for the retardation and for the birefringence. Furthermore, the light beam in the in-plane as well as in the out-of-plane beam consists of the superimposition of the respectively emitted wavelengths, ie of either the discrete wavelengths irradiated and / or the at least one wavelength range.

As already shown with reference to FIG. 1, after the exit from the sample 3 to be examined, the light wave beam LS strikes a splitting unit SPLIT in which both the light beam in the in-plane and in the out-of-plane branch is detected by means of a Beam splitter D-BSl is split into a detection light beam D-LSl and D-LS2.

The partial beam D-LS1 is fed to a separator D-SEP1 and the further light beam D-LS2 is fed to a second separator D-SEP2.

The light beam emerging from the two separators D-SEPl or D-SEP2 is then split into a spatial pattern as a function of the wavelength λ and transferred to a diffractive element DOE (DOE1 or DOE2), which will be explained in detail later a lens Ll or L2 to an analyzer element A arranged thereafter, which in the exemplary embodiment shown comprises an analyzer element Al with respect to one sub-beam D-LS1 and an analyzer element A2 with respect to the second sub-beam D-LS2. Information about the phase angle, the order, etc. of the light beam can be obtained from this image pattern - which will be explained below - with the spatial and intensity information and possibly the color (wavelength) information being determined by means of a downstream camera DETl or DET2 can be recorded and used in a computer.

In contrast to the exemplary embodiment explained above, it would in principle be sufficient to use the light beam LS of the in-plane or the out-of-plane branch (that is, the IP branch or the OP branch) only by the diffractive element DOE1 and the following Lens Ll can be irradiated to the analyzer Al, then the information about it received via the reception sensor, usually the camera DETl, record and evaluate accordingly. The use of splitting unit SPLIT ultimately serves to achieve a further improved resolution by the splitting. This unit (SPLIT) is shown on the one hand in FIG. 4 using the unit Shift shown there, around which the second detection unit D _{2 is} formed in a punctiform manner. The "Shift 1" unit also again constitutes a delay element (for example in the form of a retarder plate), for example producing a λ / 4 or λ / 2 or similar phase shift in the branched light beam, thus providing better separation between slower and faster components in the incident light beam LS allows becomes .

It can also be seen from FIG. 4 that a so-called shift unit is arranged between the coupled-out light beam D-LS1 and D-LS2, ie between the beam splitter D-BS1, which is permeable to the first light beam D-LS1 and one Partial beam decouples, which then after passing through the shift unit to the mirror RT, Ml falls and in the illustrated embodiment is deflected accordingly and thereby passes through the other wavelength separator or edge filter (in particular edge filter) D-SEP2.

The mentioned SPLIT units are shown in FIG. 1 as "SPLIT IP" and "SPLIT OP" for the IP and OP beams, if a splitting into respectively two optical paths is intended to increase the resolution

In the case of extreme resolution requirements, it may be necessary to extend the measuring range even further. For this purpose, further detection branches D ₁ to D _{N are} coupled via beam splitter BS, as indicated in FIG. 4 by the dotted outline. If, for example, one wants to detect the entire visible region with the highest resolution, for example, only a partial region of the spectrum can be radiated onto the respective diffractive element DOE and detected via an edge filter D-SEP.

The respective separator D-sepl or D-SEP2 is, for example for a certain wavelength X _1, X _2, etc. throughout to λ _N or a wavelength range A ₁ X, but blocking for a different wavelength range A ₁ X + ΔλX. For the further separator or edge filter D-SEP2 this procedure is exactly reversed. Thus, it is possible to separate the respective excitation wavelengths and ranges.

At the mirror RT, M1, a partial beam is transmitted, which then falls on the detector unit DT3, that is, a detection unit, which, as stated, is required for determining the transmission and the thickness of the film.

The detection units will be described below in more detail with reference to FIG. 1 and in particular also with reference to FIG. 5 et seq.

In this case, the detection units 9, i. the detection units 9a and 9b, constructed analogously for the two beam paths in-plane and out-of-plane, which is why only one detection component for a beam branch is described below. Basically, these detection units 9 or 9a and 9b comprise the diffractive element DOE, the lens L1 or L2, the analyzer element A1 or A2 and finally the measuring unit or sensors DET1 or DET2 used for the detection, which preferably consist of a camera.

The basic components of the detection unit 9 are based on the aforementioned diffractive element DOE and a downstream analyzer unit A. The detection principle is first explained with reference to FIG. 5 with regard to its basic principle of operation with reference to a method known from the prior art.

If it is assumed that, for example, a light beam LS having only one wavelength X _{1 is} irradiated into a sample 3 to be examined, then the light beam LS, after passing through the polarization-maintaining diffuser, is irradiated. fractal element DOE in a vorbestiramtes pattern, ie, a predetermined diffraction pattern pattern BM imaged. In the example shown with reference to FIG. 5, the light beam LS is split or fanned out into N partial beams by the diffractive element DOE, which form an image in circular areas 15 on an analyzer arrangement A to be discussed below, these circular areas 15 and so that the diffraction pattern BM are symmetrical around a pitch circle.

This diffraction structure pattern is thus irradiated to the mentioned analyzer arrangement A, the analyzer arrangement A comprising individual analyzers in the form of polarizers at each imaging position 115 (ie in the region of each individual circle 15 in FIG. 5) are arranged at certain angles to each other. In the illustrated exemplary embodiment according to FIG. 5, each individual analyzer 19 is rotated with its plane of polarization by 15 ° with respect to the polarization plane of an adjacent individual analyzer.

In general, therefore, a light beam LS is split by the mentioned diffractive element DOE into N partial beams. The polarization orientations of the individual analyzers are in angles of

a - • i

^~ N

where i = 1, 2, 3, ..., N are the natural integers, and N is the number of particle beams and thus the number of individual analyzers corresponds.

Depending on the phase angle of the birefringent medium, an intensity pattern BS arises behind the analyzer arrangement, which can be detected, for example, with individual diodes, line arrays or full-area sensors. In particular, LCD cells or, for example, CCD cameras, etc. are suitable for this purpose.

By means of the above, explained with reference to Figure 5 analyzer arrangement can therefore determine the phase angle, the spatial structure may be arbitrary. The measuring method for the conversion of a temporal polarization information into a spatial one explained so far is basically known from the above-mentioned prior publication DE 195 37 706 A1.

With reference to FIG. 6, in contrast to FIG. 5, the measuring method according to the invention will now be explained in more detail.

In accordance with the invention, it is now provided that the wavelength-dependent diffractive properties of the diffractive element DOE are used for the simultaneous detection of the polarization properties (retardation) of a plurality of discrete wavelengths and / or at least one wavelength range.

If a light beam hits the diffractive element DOE, which radiates in a plurality of discrete wavelengths and / or in at least one wavelength range, analogous patterns, ie analog diffraction pattern B, are generated as a function of the wavelength, depending on the design of the diffractive element used DOE Lich are separated or may be spatially separated and are polarization-preserving at each sample location.

FIG. 6 shows the principle representation according to the invention of the wavelength selectivity of a diffractive element DOE with an analyzer arrangement using the example of three discrete wavelengths X ₁ , λ ₂ and X ₃ . If, unlike FIG. 6, no analyzers, ie no polarizers, were used, the same image pattern reproduced in FIG. 6 would result, but then the intensities at all image positions would be the same on the respective pitch circles.

With the wavelength selectivity of the diffractive element DOE, a spatial separation as a function of the wavelength is thus possible. A diffraction pattern BM is generated whose individual components also all contain the same polarization information for the respective wavelength. If, as explained, an analyzer A with defined but mutually different polarization angles is brought before each individual pattern (in FIG. 5 or 6 the respective circular area 15 at the relevant imaging position 115), then the phase angle of the birefringent medium can be at different wavelengths or wavelength ranges be detected at the same time. So you can capture the polarization properties in a wide wavelength range and at higher orders at the same time.

The diffraction pattern BN reproduced in a spatial representation in FIG. 6 is reproduced once again in a planar view in FIG. 7, whereby at each image position 115 (with the circular surfaces 15 in the exemplary embodiment shown). Then, an analyzer A is positioned in the form of a single analyzer 19, which, as explained above, in the embodiment shown has an orientation of the polarization plane deviating by 15 °.

In the embodiment according to FIGS. 6 and 7, a diffraction pattern is reproduced as an example, depending on the diffractive element DOE used. The image function according to FIGS. 6 and 7 shows an image or diffraction pattern for the case in which a light beam having a plurality of discrete wavelengths (which therefore differ from one another) is used for the sample to be examined. If, instead of discrete wavelengths for the sample to be examined, a light beam is used which comprises a wavelength range, the patterns merge into one another, as is reproduced, for example, in FIG. 7 by the oval borders 115 '.

In other words, in FIG. 7, along the double-arrow representation WW, it is indicated which image points are generated as a function of the wavelength change. According to the arrow diagram DisP, the discrete polarization imaging points or areas are indicated, ie those areas in which the light beam is imaged at different locations as a function of the polarization.

In accordance with the diffraction pattern BM generated as a function of the diffractive element DOE used, an analyzer arrangement A that has been appropriately matched must therefore also be used or an analyzer arrangement must be designed accordingly. If these are a few discrete wavelengths, an analyzer arrangement A also be produced using discrete analyzer elements 19. At each pattern position, a single analyzer 19 is then attached to the analyzer element at a defined angle, as already described above. Otherwise, an entire analyzer arrangement with corresponding sections and areas must be generated or adapted accordingly, these areas having to have, for example, 115 'for the evaluation of the corresponding polarization information correspondingly aligned polarization areas.

With the exception of FIG. 7, another example is shown with reference to FIG. 8 if another diffractive element DOE is used, which leads to a different image function. Also in this case, one of the individual image position 115 (which in each case consists of a square area in FIG. 8) must be positioned corresponding to analyzer individual elements 19, or else a common analyzer comprising individual structured analyzer sections 19 is used, which are adapted for detection of a particular polarization orientation according to the arrow representation. This is only intended to show that the most varied image positions and arrangement of analyzers are conceivable and possible, depending on the diffractive element DOE used.

From the above explanation, it follows that at several discrete wavelengths or wavelength ranges, however, the analyzer pattern is then practically no longer producible. Therefore, the analyzer element provided according to the invention is provided in the form of the individual analyzers 19, for which three paths are available: i) it is possible to use discrete single analyzers 19 in the form of single polarizers 19a, as described above,

ii) lithographic or holographic use and preparation of an analyzer element is possible, or

iii) it is possible to use an analyzer element using the structure of an LCD device.

With regard to the above-mentioned use of lithographic or holographic Analysa- tor elements lends itself to the use of lithographically or holographically produced polarization grating arrays on. Each pattern element, which is arranged in dependence on the DOE pattern, then has a defined polarization position. As indicated in FIGS. 6 to 8, the analyzer elements are arranged rotated in relation to each other at least in the range from 0 to π. The more single analyzers arranged in this area, the higher the resolution of the phase angle becomes.

Since the rotation of the polarization in an LCD cell is voltage-dependent, with respect to the above-mentioned third variant, within the resolution of an LCD screen, each LCD cell having a certain polarization angle can be adjusted. In a calibration method, therefore, light of a wavelength can be imaged by the diffractive element DOE on the LCD screen. For each illuminated pattern, a defined polarization orientation is then impressed on the individual LCD cells and stored in the computer. puts. The so-called calibration procedure is then repeated for any other wavelengths. Thus, it is thus possible to provide a high resolution polarization arrangement with the resolution of an LCD screen.

By means of the illustrated measuring method and the described measuring structure can be determined in connection with the described detection unit, a series of information, namely

1) The detector is wavelength selective. Depending on the wavelength, a defined spatial pattern is formed according to the DOE structure. The pattern scattered by the DOE is polarization-preserving. The spatial structure defines the wavelength.

2) The generated pattern allows the individual analyzer elements to determine the phase angle and thus the retardation of the birefringent medium. Schematically, for example, the polarization ellipses of three discrete wavelengths with their phase angles are shown in FIG. Since the detection takes place at the same time, a different phase angle is therefore present for each wavelength (Δφ = 2πR / λ) because of the wavelength dependence of the retardation. In practice order jumps (R> nλ, n = 1..N) occur and Δφ - 0, nπ. Since it is possible with the arrangement to determine the phase angle at quasi-discrete wavelengths in each case and the phase angle changes inversely with the wavelength, it is possible to detect the wavelength-dependent order jump directly via a minimization method. 3) Since the position of the polarization elements is known and the phase angle can be determined from the intensity measurement, the determination of the principal axes and the amplitude of the double calculation is also known, which in turn can be used for the determination of the Mueller matrix.

4) With the application of at least two closely spaced wavelengths, the order of birefringence can be determined online and time synchronously.

5) For optical films, the retardation in a wide wavelength range can be determined online and synchronously.

6) Is the intensities (I ~ cos ² (πR / λ f (λ)) are integrated) of a wavelength pattern, so the retardation can be determined in addition to the phase angle information, which increases the resolution higher.

7) As stated above under point 6), the transmission can additionally be determined for each wavelength, since the irradiated intensity is also measured in each excitation.

8) Through the determination of the transmission at several wavelengths, the thickness of the sample can be determined via the Lambert-Beersche law.

The detection and evaluation of this information explained above is then preferably done in a full-frame CCD camera, which in Figure 1 and Figure 5 as DETl and DET2. These cameras are then not only provided for the in-plane radiation branch IP, but also for the out-of-plane radiation branch OP, so that a total of four such cameras DET are then used.

Assuming, for example, that the sample to be examined, in particular in the form of a film web to be examined, moves forward at 600 m / min, then with a measuring beam diameter of, for example, 10 mm for the light beams, the pole angles could be determined every 10 ms become. However, since different polarization properties can show per measuring point volume, averaging over several measuring points is appropriate or necessary.

Finally, it should be pointed out that a basic prerequisite for the resolved detection of the transmissions through the sample to be examined is to know or detect the intensities of the excitations of the light beams. In the case of excitation, this is ensured by the fact that the irradiated intensities can be detected in the detector devices DET1, DET2, as shown with reference to FIGS. 2 and 3, respectively. Because in the case of the beam splitters reproduced there, one respective sub-beam serving for the intensity adjustment can be coupled out of each of the coupled-out beams for the first or the second wavelength or the first or second wavelength range, which can be measured via the mentioned detector devices DET1 and DET2.

After the transmission spectrum has been measured, the thickness of the sample can also be determined by the Lambert-Beersche law are determined, which in turn is used to calculate the birefringence values. Of course, the thickness information from external measuring devices of the thickness can also be used for this determination.

Finally, the calibration and calibration of the device according to the invention will be discussed.

For calibration, a monochromator or other discrete wavelengths are used. For a discrete wavelength, the location on the analyzer unit and its imaging on the camera, that is to say in the detection device DET1 or DET2, is then determined.

Another calibration method is the use of spectral lines of white light sources (spectral lamps). These allow continuous self-calibration during operation.

Similarly, discrete laser wavelengths superimposed on the white light source or discrete erasures generated by notch filters could be used as calibration points.

By means of this calibration method, it is therefore possible to determine the wavelength-dependent impingement points in the image pattern on the analyzer device, even if the image patterns result, for example, in oval or elongated image positions which extend over a wavelength range.

For samples, in particular in the form of transparent or semi-transparent plastic films, for which R <λ, occur at a rotation of the polarization ellipse umd π maximum Retardationsunterschiede at R (700 nm) to R (400 nm) of a maximum of 150 nm. With these films, it is not necessary to use a second wavelength. Rather, the entire wavelength range can be measured and calibrated with a simplified arrangement.

In principle, it is sufficient here to carry out a corresponding calibration measurement with a few wavelengths. The rest of the spectrum can be adjusted mathematically.

For higher order films, e.g. the spectrum of the excitation LSl with the wavelength λl are continuously passed through with the maximum sampling rate of the detection unit or detection camera DETl. At defined wavelengths of λl, a so-called probing pulse of wavelength λ2 = λl + Δλ is fed, which may possibly have a higher intensity than λl. In order to ensure the higher intensity, the average intensity of λ1 is measured by means of the detector DT3 (shown in FIG. 4) and the intensity of λ2 is accordingly adjusted, which results in a higher signal level at the detectors, which differs from the signal of λ1 allows. Eventually, this probing pulse can also be used with a different polarization.

Claims

Claims:

1. A method for measuring the birefringence and / or the retardation of samples (3), in particular in the form of running film webs consisting of single or multi-layer transparent or partially transparent plastic films, with the following features by means of at least one light source (LQL, LQ2) or by means of two Light sources (LQ1, LQ2), two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) are generated,

- The two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) are directed at different angles to each other on the sample (3) and irradiate the sample to be analyzed (3) at different angles,

the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) pass through the sample (3) at the same position (X) or a sample area (X) narrowly bounded with respect to the sample size and / or sample width,

the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) passing through the sample (3) to be analyzed encounter a detector device (9; 9a, 9b), characterized by the following further features

the light beams (LS1, LS2, LS1_1, LS1_2, LS2 1, LS2 2) passing through the at least two sample (3) to be analyzed are generated in such a way that they produce light waves comprising at least two discrete wavelengths (λ _{1 (} λ ₂ , ...) and / or at least one wavelength range (λ _x ),

Both light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) pass through a polarization-maintaining, diffractive element (DOE, DOE1, DO2), whereby the light beam (LS1) passing through the diffractive element (DOE, DOE1, DO2E2) passes through , LS2, LS1_1, LS1_2, LS2_1, LS2_2) into a plurality of partial beams with a diffraction structure dependent on the diffractive element (DOE, DOE1, D0E2) and on the wavelength of the light beam (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2). Pattern (BM) is split and / or mapped, and

a detector device (9; 9a, 9b) with polarization-sensitive analyzers (A; Al, A2; 19) is used, wherein the polarization-dependent intensity at the imaging positions (115, 115 ') is detected by means of the detector device (9; 9a, 9b). ) of the diffraction pattern (BM) generated by the partial beams and, depending thereon, the phase angle and thus the retardation of the birefringent sample (3).

2. Method according to claim 1, characterized in that both light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) pass through a polarization-maintaining diffractive element (DOE, DOE1, DOE2), by way of which a light-wave length-dependent diffraction pattern is generated.

3. Method according to claim 1 or 2, characterized in that, by means of the wavelength selectivity of the diffractive element (DOE, DOE1, D0E2), a spatial separation of the partial beams is produced as a function of the wavelength or the wavelength range, wherein the wavelengths in the The same direction deflected partial beams with different discrete wavelengths (X ₁ , A ₂ , ..., A _N ) or at least one wavelength range ((A ₁ X) containing the respective polarization information.

4. Method according to one of claims 1 to 3, characterized in that a wavelength-dependent diffractive element (DOE, DOE1, DOE2) is used, over which one of the wavelengths of the light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2 ), which run through the sample to be examined (3), dependent analog diffraction pattern (BM) for the two light beams (LSl, LS2, LS1_1, LS1_2, LS2_1, LS2_2) is generated, wherein a) when using light beams (LSl, LS2, LS1_1, LS1_2, LS2_1, LS2_2), which are in different discrete

Wavelengths (A ₁ , A ₂ , ..., A _N ) radiate, a diffraction pattern (BM) with separate imaging positions (115), or b) when using light beams (LS 1, LS 2, LS 1_1, LS 1_ 2, LS 2_1, LS 2_2) emitting in at least one wavelength range (A ₁ X), a diffraction pattern (BM) having contiguous imaging positions (115 ') is generated on the analyzer (A; Al, A2; 19).

5. Method according to one of claims 1 to 4, characterized in that N differently polarized analyzer elements (A; Al, A2; 19) or one or more analyzer elements are used, the total N differently polarized analyzer Sections, namely for N partial beams, for their polarization orientation 180

i = 1, 2, ..., N holds.

6. The method according to any one of claims 1 to 5, characterized in that one of the analyzer assembly (A; Al, A2; 19) downstream detector means (DET; DETl, DET2) is used, the individual diodes, line arrays and / or full-surface sensors, in particular in the form of CCD cameras, etc.

7. The method according to any one of claims 1 to 6, characterized in that the phase angle of the birefringent

Sample (3) at different wavelengths or at least one wavelength range of the light beams used (LSl, LS2, LS1_1, LS1_2, LS2_1, LS2_2) is detected at the same time.

8. Method according to claim 1, characterized in that light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2 ), which pass through a wavelength separator (WS1, WS2) arranged downstream of the at least one or both light sources (LQ1, LQ2), wherein the generated light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) in two mutually offset wavelength ranges, in an overlapping wavelength range and / or radiate in an overlapping or equal wavelength range.

9. Method according to one of claims 1 to 8, characterized in that: a diffractive element (DOE, DOE1, D0E2) is used, by means of which the partial beams preferably generate discrete circular or oval or other image positions (115, 115 '), which fall through the polarization-selective analyzer and strike the detector device (DIT, DIT1, DIT2).

10. The method according to any one of claims 1 to 9, characterized in that an analyzer (A; Al, A2; 19) is used which consists of a lithographic or holographic analyzer element.

11. The method according to any one of claims 1 to 10, characterized in that an analyzer (A, Al, A2, 19) is used, whose structure consists of an LCD arrangement.

12. The method according to any one of claims 1 to 11, characterized in that a preferably color-selective analyzer (A, Al, A2, 19) is used, which consists of a CCD camera, in particular a full-frame CCD camera.

13. The method according to any one of claims 1 to 12, characterized in that an analyzer (A, Al, A2, 19) is used, which comprises a plurality of individual analyzer elements (19) whose polarization planes are oriented differently, or from a Analyzer arrangement (A; Al, A2) which comprises a plurality of regions with different polarization orientations corresponding to the image positions (115, 115 ') of the diffraction pattern (BM), depending on the diffractive element (DOE, DOE1, DOE2) used ,

14. Method according to one of claims 1 to 13, characterized in that the one light beam (LS1, LS2, LS1_1, LS2_1) perpendicularly intersects the sample (3) to be examined, preferably in the form of a film, and the second light beam (LS1, LS2). LS2, LS1_2, LS2_2) at an angle to the sample to be examined (3), preferably in the form of a film.

15. The method according to any one of claims 1 to 14, characterized in that two separate light sources (LQl,

LQ2) are used to generate the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2).

16. Method according to one of claims 1 to 14, characterized in that only one light source (LQ1) is used, from which a partial beam is branched off, so that the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) through the sample to be examined (3) at an angle to each other.

17. The method according to any one of claims 1 to 16, characterized in that two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) are used whose wavelength range is in a range of 2 to 20%, preferably 4 to 16% , especially 8 to 12%.

18. Method according to claim 1, characterized in that a wavelength is used for the light beams used (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) whose wavelength difference Δλ is greater than 4 nm, in particular larger is as 6, 8 or 10 nm.

19. The method according to any one of claims 1 to 18, characterized in that two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) are used whose wavelengths differ by less than 100 nm, in particular less than 80, 60, and in particular less than 40 nm.

20. Method according to one of claims 1 to 19, characterized in that by means of the analyzer elements (A; Al, A2; 19) and the downstream detector device (DET; DET1, DET2) the phase angle of the light beam (LS1, LS2; LS1_1, LS1_2, LS2_1, LS2_2) and thus the retardation and / or the birefringence value and indirectly the refractive indices of the sample to be examined (3) is determined.

21. The method according to any one of claims 1 to 20, characterized in that in the detection range of the sample to be examined (3) radiating light beam (D-LSL, D-LS2, ..., D-LSN) in N beams with different wavelengths or a different wavelength range, where N = I, 2, ... is a natural number, and the wavelength-dependent light beams are each supplied to a diffractive element (DOE, DOE1, DOE2).

22. The method according to claim 21, characterized in that the light beams (D-LS1, D-LS2, ..., D-LSN) before impinging on the analyzer (A; Al, A2, 19) a lens (Ll, L2, ..., N).

23. The method according to claim 22, characterized in that the wavelength-dependent separated light beams (D-LSL, D-LS2, ..., D-LSN) each have a wave, wavelength separator or filter (D-SEPL, D-SEP2 , ..., D-SEPN) before passing through the respective downstream diffractive element (DOE, DOE1, DO2, ..., DOEN).

24. Method according to claim 23, characterized in that a wavelength separator or filter (D-SEPL, D-SEP2,..., D-SEPN) is used in the detection area in each partial wave beam, which is constructed such that a wavelength separator or filter (D-SEPL) is transparent for a certain wavelength or a certain wavelength range and blocks for another shifted wave range, whereas the decoupled second light beam (D-LS2) is just inversely blocked or permeable.

25. The method according to any one of claims 21 to 24, characterized in that between the coupled-out light beams (D-LSL, D-LS2, ... D-LSN) in each case a shift unit (SHIFT) is used, by means of which a Phase shift of preferably λ / 4 or λ / 2 is performed.

26. The method according to any one of claims 1 to 26, characterized in that beam splitters are provided, by means of which in each case a partial beam can be coupled, which falls on downstream detectors (DTl, DT2, DT3, ..., DTN), wherein the decoupled Light beams are used when the light beam generated by a monochromator.

27. Device for measuring the birefringence and / or the retardation of samples (3), in particular in the form of running film webs consisting of one or more layers transparent or partially transparent plastic films with the following features having a radiation arrangement with at least one light source (LQ1, LQ2) or with at least two light sources (LQ1, LQ2) for generating two light beams (LS1, LS2, LS1-I, LS1_2, LS2_1 , LS2_2), the beam arrangement is such that the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) are directed at different angles to each other onto the sample (3) to be examined and can radiate through at different angles Arrangement of the beam is constructed in such a way that the two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) pass through the sample (3) at the same position (X) or a narrowly bounded sample area (X) with respect to the sample size and / or sample width Furthermore, a detector device (9; 9a, 9b) is provided, in which the light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) can be measured, which have passed through the sample (3) to be analyzed It is at least one and preferably at least two light sources (LQ1, LQ2) and optionally at least one or preferably two wavelength separators (WS1, WS2) are provided, via which at least two light beams (LS1, LS2; LS1_1, LS1_2; LS2_1, LS2_2) whose light waves comprise at least two discrete wavelengths (λ _{1 #} λ ₂ , ...) and / or at least one wavelength range (λ _x ), - a polarization-maintaining, diffractive element (DOE, DOE1, DOE2 ), over which the light beam (LS1, LS2, LS1, LS1, LS2, LS2) falling through the diffractive element is divided into a plurality of light beams. the number of partial beams is split and / or imaged with a diffraction pattern (BM) dependent on the diffractive element (DOE; DOE1, D0E2) and on the wavelength of the light beam (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2); a detector device (9; 9a, 9b) with polarization-sensitive analyzers (A; Al, A2; 19) is provided by means of which the intensity of the diffraction pattern (BM) generated by the partial beams is used to determine the phase angle and thus the retardation of the diffraction pattern birefringent sample (3) is measurable.

28. Device according to claim 27, characterized in that two polarization-maintaining diffractive elements (DOE, DOE1, D0E2) are provided, namely in each case a diffractive element (DOE1, DO2) for a light beam (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) ).

29. Device according to claim 27 or 28, characterized in that a wavelength-dependent diffractive diffraction pattern (BM) is provided for generating a wavelength-dependent diffractive element (DOE, DOE1, DO2), by way of which separate image positions (115 ) on the analyzer (A, can be generated 19) when the light beam used (LSI, LS2; Al, A2 LS1_1, LS1_2; LS2_1, LS2_2) (in discrete wavelengths X _1, λ _2, ..., λ _N) shine.

30. Apparatus according to claim 27 or 28, characterized in that a wavelength-dependent diffractive structure pattern (BM) is provided for generating a wavelength-dependent diffractive element (DOE; DOE1, D0E2), which is dependent on the wavelength. sainmenhängende image positions on the analyzer (A 19; Al, A2) ^(115?) can be generated when the light beam used (LSI, LS2; LS1_1, LS1_2; LS2_1, LS2_2) in a wavelength range (X ₁ X) irradiated.

31. Device according to one of claims 27 to 30, characterized in that N-differently polarized analyzer elements (A; Al, A2, 19) or one or more analyzer elements are provided, the total N-differently polarized analyzer Comprise sections, namely for N partial beams, for their polarization orientation

^ 80 a = • i

N

where i = 1, 2, ..., N.

32. Method according to claim 27, characterized in that a detector device (DET, DET1, DET2) arranged downstream of the analyzer arrangement (A; Al, A2; 19) is provided, the individual diodes, line arrays and / or full-area sensors, in particular in the form of CCD cameras, etc.

33. Device according to one of claims 27 to 32, characterized in that a measuring device for measuring and evaluation of the phase angle of the birefringent sample (3) is provided by means of the phase angle at different wavelengths or at least one wavelength range of the light beams (LSl, LS2, LS1, LS1 2; LS2_1, LS2_2) can be detected at the same time.

34. Device according to one of claims 27 to 33, characterized in that the phase angle of the birefringent sample (3) using two light beams (LSl, LS2, LS1_1, LS1_2, LS2_1, LS2_2) is simultaneously detectable, wherein the at least two used light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) radiate in two mutually offset wavelength ranges, in an overlapping wavelength range and / or in an overlapping or equal wavelength range.

35. Device according to one of claims 27 to 34, character- ized in that a diffractive element (DOE;

DOE1, DOE2) is provided, by means of which the partial beams respectively form discrete circular or oval imaging positions (115, 115 '), which pass through the polarization-selective analyzer and hit the detector device (DIT, DIT1, DIT2).

36. Device according to one of claims 27 to 35, characterized in that an analyzer (A; Al, A2; 19) is provided which consists of a lithographic or holographic analyzer element.

37. Device according to one of claims 27 to 36, characterized in that an analyzer (A; Al, A2, 19) is provided, whose structure consists of an LCD arrangement.

38. Device according to one of claims 27 to 37, characterized in that an analyzer (A, Al, A2, 19) is provided, which consists of a CCD camera, in particular a full-frame CCD camera.

39. Device according to one of claims 27 to 38, characterized in that an analyzer (A, Al, A2, 19) is provided, which comprises a plurality of individual analyzer elements (19) whose polarization planes are oriented differently, or from an analyzer arrangement (A; Al, A2) which has a plurality of regions with different orientations of the polarizations corresponding to the image positions (115, 115 ') of the diffraction pattern (BM) as a function of the diffractive element (DOE, DOE1, DOE2) used. includes.

40. Device according to one of claims 27 to 39, characterized in that the overall arrangement is such that one light beam (LS1, LS2, LS1_1, LS2_1) perpendicular to the sample to be examined (3), preferably in the form of a film and the second light beam (LS1, LS2, LS1_2, LS2_2) at an angle to the sample to be examined (3), preferably in the form of a film.

41. Device according to one of claims 27 to 40, characterized in that two separate light sources (LQL, LQ2) are provided, by means of which two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) can be generated.

42. Device according to one of claims 27 to 41, characterized in that only one light source (LQI) is provided, from which a partial beam can be branched off, about which two angularly aligned light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) for irradiating the sample to be examined (3) in angled Orientation can be generated to each other.

43. Device according to one of claims 27 to 42, characterized in that two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) can be generated, the wavelength range of two 2 to 20%, preferably 4 to 16%, in particular 8 to 12% different.

44. Device according to one of claims 27 to 43, characterized in that the light beams (LS1, LS2;

LS1_1, LS1_2; LS2_1, LS2_2) comprise light beams with different wavelength whose wavelength difference Δλ is greater than 4 nm, in particular greater than 6, 8 or 10 nm.

45. Device according to one of claims 27 to 44, characterized in that two light beams (LS1, LS2, LS1_1, LS1_2, LS2_1, LS2_2) can be generated whose wavelengths are less than 100 nm, in particular less than 80, 60, and especially less than 40 nm.

46. Device according to one of claims 27 to 45, characterized in that by means of the analyzer elements (A; Al, A2, 19) and the downstream detector means (DET; DETl, DET2), the phase angle of the light beam (LSl, LS2, LS1_1 , LS1_2, LS2_1, LS2_2) and thus the retardation and / or the birefringence index of the sample to be examined (3) can be determined.

47. Device according to one of claims 27 to 46, characterized in that in the detection region for the sample to be examined (3) N diffractive elements (DOE, DOEl, D0E2, ..., DOEN) are provided, which are irradiated by light beams (D-LS1, D-LS2, ..., D-LSN) divided into N partial beams and passing through the sample (3) to be examined.

48. Apparatus according to claim 47, characterized in that the diffractive element (DOE, DOE1, DO2, ..., DOEN) is followed by a lens (L1, L2, ..., N) or the analyzer (A1; A2, ..., AN; 19) is preceded by a lens (LS1).

49. Apparatus according to claim 48, characterized in that N wavelength separators or filters (D-SEPl, D-SEP2, ..., D-SEPN) are provided, each of a wavelength-dependent separate light beam (D-LSL, D -LS2, ..., D-LSN) before hitting a downstream diffractive element (DOE, DOE1, D0E2, ..., DOEN).

50. Apparatus according to claim 49, characterized in that in the detection area in each sub-wave beam, a wavelength separator or filter (D-SEPl, D-SEP2, ..., D-SEPN) is provided, which is constructed so that a wavelength separator or filter (D-SEPL) is transparent for a certain wavelength or a certain wavelength range and blocks for another shifted wave range, whereas the decoupled second light beam (D-LS2) is just inversely blocked or permeable.

51. Device according to one of claims 47 to 50, characterized in that between the decoupled light beams (D-LSL, D-LS2, ..., D-LSN) each have a Shift unit (SHIFT) is arranged, by means of which a phase shift of preferably λ / 2 or λ / 4 is feasible.

52. Device according to one of claims 27 to 51, characterized in that when generated by means of a monochromator light beam (LS) beam splitter (D-BSl, D-BS2, ..., D-BSN) are provided, by means of which in each case a partial beam (D-LS1, D-LS2, ..., D-LSN) can be decoupled, which falls on downstream detectors (DTl, DT2, ..., DTN).