DE19935631C1 - Ultra-short laser pulse characterisation method uses multi-channel correlation technique with matrix of phase elements for providing Fabry-Perot effect generating characteristic interference rings - Google Patents

Abstract

The characterisation method uses a multi-channel correlation technique in which parts of the beam are superimposed on themselves via a matrix (2) of phase elements (3a,3b) supported by a transparent substrate, with the phase elements and the substrate having different refractive indices, for total internal reflection within the phase elements for providing a Fabry-Perot effect, generating characteristic interference rings (5). Different phase elements or phase element groups have different phase profiles for multi-channel processing of the beam, with detection of the interference patterns via a detector (7) in the form of a matrix camera. An Independent claim for a device for characterisation of ultra-short laser pulses is also included.

Description

The invention relates to a method and an arrangement for the temporal characterization of ultra-short Laser pulses.

For a wide range of laser applications ultra-short impulses such as material processing, process control, laser spectroscopy, medicine, environmental sensors and communication is an increasing need reliable and compact single-shot measuring devices for the simultaneous recording of the relevant parameters of the Radiation. Real-time diagnostics is essential for that Optimization of high power laser systems, especially in Oscillator-amplifier arrangements with adaptive resona gate optics, and control of the nonlinear beam propagation in such systems. Growing interest of ultra-short-term measurement technology is also in new fields like quantum control with learning feedback too record.

Phase and polarization sensitive detection tran Processes on the FS time scale are in the Semiconductor technology important in the study of Quantum wells for coherent destruction  photo-induced excitons, the detection of exciton Exciton interactions or coherent control of electron LO phonon scattering in bulk semiconductors.

The illustration of objects in scattered or turbu lent media with short deadlines is for biomedicine and other applications essential.

The prior art is different Methods and arrangements for spatial-temporal Characterization of ultrashort laser pulses known with which information about phase coherence, intensity course and / or spectral properties can be obtained can. The disadvantage is that these processes are complex and are of limited time resolution and some Procedures follow reproducible impulses needed become. For characterization non-reproducible tangible impulses and the acquisition of parameter accuracy However, single-shot measurements are indispensable.

The known measuring arrangements can be divided into two Classify basic variants, each with either two sub-beams are collinearly superimposed be changed and the optical path in one arm must be (typically not for single pulses suitable) or non-collinear (crossed) superimposed (suitable for single impulses).

The linear superposition of the partial beams produces one interferometric correlation measurement (e.g. the car first order correlation function), which is a statement delivers on the temporal coherence of the laser pulse.  

For autocorrelation measurements with non-linear over storage, d. H. sufficient for multi-photon processes Intensity, the proportions of the laser beam sequentially or simultaneously in suitable media stores and about optically effective nonlinear changes effects like the generation of the second harmonic (SHG), two-photon fluorescence (TPF) or Two-photon absorption (TPA) detected.

The information about the pulse length is transformed both in the collinear and in the non-collinear superposition of the beams into spatial information (length of an interaction zone or path length of a shift) and read out optically or electrically. If the crystal-specific parameter χ ^{(2) is known} , a single-shot and single-beam method based on the SHG can be used, but it is associated with relatively large errors (30% in the ps range).

A complete impulse characterization is by means of successive measurements of the spectrum, the Intensity and phase autocorrelation possible. At the latter, the phase becomes sequentially interferometric measured, the range of temporal coherence by phase shift between the pulses is scanned.

DE 39 26 945 A1 describes a device for measuring the duration of individual short optical radiation pulses by means of autocorrelation and two-photon ionization, with  a machine designed as a beam splitter device Zehnder interferometer, known.

DE 31 08 177 C2 describes one method and one Device for measuring the duration of, individual coherent radiation pulses, each one coherent radiation beam with perpendicular to it Form the direction of propagation of the wavefront using a diffraction grating for delay the rays of the radiation beam.

With a further developed technology, reversible optical transformations for pulse extension exploited, whereby from signal and transformed signal Cross correlations need to be determined what considerable analytical and numerical effort caused.

In the so-called SPIDER method (Spectral Phase Interferometry for Direct Electric-Field Reconstruction of ultrashort optical pulses. - Opt. Lett. 23 ( 1998 ), 792-794), a chirped pulse (with a continuous frequency) is used with a pair of non-chirped ones Shares overlaid in a nonlinear crystal, whereby multi-photon processes are used (e.g. Upcon version or SHG). In this way (similar to a spectral shearing interferometer) a spectral interferogram is generated, whereby no iterative methods are used for the evaluation.

SPIDER, FROG and interferometric autocorrelation (IAC) are currently getting the shortest impulses (around 5 fs) their resolution limits.

The introduction of a transverse time delay into a reference pulse through a grating is used in another known technical solution for pulse correction [K. Oba, P.-Ch. Sun, YT Mazurenko, Y. Fainman: Femtosecond Single-Shot Correlation System: A Time-Domain Approach. - Appl. Opt. 38 ( 1999 ), 3810-3817]. The signal and reference pulse are mixed in a nonlinear crystal, so that the SHG receives the time profile as spatial information. The time window is limited by the size of the grating aperture.

The object of the invention is a Ver drive and develop an arrangement of the type mentioned, with which the Disadvantages of the prior art can be avoided and with those based on a compact structure a correlator technique a measurement of the time course the intensity with very high time resolution Single shot operation is achieved and also information about the spatial or temporal phase distribution of the Laser field can be obtained.

The object of the invention is achieved by a method according to claim 1 and an arrangement according to claim 13 solved.

The method and arrangement according to the invention are thereby characterized in that the time-resolved characters of ultra-short laser pulses with a  Multi-channel correlator technology, in which an inter ferometric overlay of parts of the beam with itself in a matrix of phase elements a transmitting substrate, one of the Refractive index of the substrate different Have refractive index by taking advantage of internal Reflection in the phase elements and with it achievable Fabry-Perot effect in a way it is made that characteristic inter reference patterns like rings are created that Phase elements or different groups of Phase elements different from each other Have phase profiles and thus the momentum in correspondingly many channels simultaneously Interference capability is tested, according to the figure Interference pattern on one as a matrix camera trained detector an electronic and / or mathematical processing of the interference pattern takes place and in this way information about the Coherence length or over time and space Intensity course can be obtained.

This is a special variant of the method characterized in that a holographic overlay of Shares the phase elements and the substrate have passed through, separated with a beam splitter ten or passing alongside the phase elements Divide the beam, each as a reference part serve on a detector or in a suitable Medium that is directly in front of the detector or is mapped on this, with a Measurement hologram arises, and via suitable mathematical procedures from the detected Intensity distribution information about the spatial  Distribution of the wave field, preferably over the Phase distribution of this wave field can be obtained. Here is the previous calibration with a well-defined reference wave, e.g. B. one with a cw Laser generated approximately flat wave, required Lich. The reference hologram generated with this will saved and then in single-shot mode when using the laser wave to be measured in each case recorded holograms with this stored Reference hologram compared.

The functioning of those formed from phase elements Matrix (matrix correlator) can be linear or be chosen non-linear, the scheme in the first Case with an interferometric autocorrelator corresponds to spectral resolution and data on the Phase autocorrelation or temporal coherence returns, in the second case, however, the time course of the Intensity. In both cases you also get one spatial resolution of the measured parameters or a part of the measured parameters over the Cross section of the pulse.

Prerequisite for the creation of interference patterns is that multiple internal reflections take place and the phase elements (depending on the surface profile) like location-dependent Fabry-Pérot etalons or Newton Interferometers work. The angular relationships of the Beam courses in the phase elements must be selected in this way be that there is no disruptive total reflection.  

When phase elements of refractive index n ₂ applied to a substrate of refractive index n _{1 are} illuminated with a plane wave, interference strips or rings are formed behind the phase elements even in the near field without reflective coatings if the refractive indices differ measurably (e.g. lacquer with a refractive index of 1.7 on a glass plate with a refractive index of 1.5) and the optical path in the phase elements varies depending on the location, e.g. B. with a wedge, a prismatic, spherical, parabolic or pyramid shape.

Advantage of straight top surfaces (wedge, prism, pyramid) is the possibility of equidistant interference fringes to be able to generate. Is the substrate sufficiently thick? or the pulse is short enough, none interfering interference from the substrate itself caused (this also applies to imaging optics and detector window).

Thin-layer microlenses can be used as phase elements of the matrix correlator, which use existing technologies that are well established in microelectronics and optics (vacuum evaporation with masks [R. Grunwald, S. Woggon, R. Ehlert: Fabrication of thin-film microlens arrays by mask -shaded vacuum deposition. - in: S. Martellucci, AN Chester (Eds.): Diffractive Optics and Optical Microsystems. - Plenum Press, New York / London 1997 , 169-177 .], etching techniques, photolithography). The advantages are the lower dispersion and the avoidance of errors caused by waviness of the substrate or shape deviations of macroscopic components, since small location-dependent transit time differences, which are unavoidable in the case of area detection over the beam cross-sectional area, are also clearly noticeable on the fs time scale. For a wavelength of 1 µm and a refractive index of 1.5, a tolerance of λ / 5 corresponds approximately to a time resolution error of 1 fs. Larger errors can occur with large areas. Components with a minimally wavy surface are costly and must have corresponding minimum thicknesses for processing reasons, which in turn leads to dispersion effects. The division into small individual phase elements in multi-channel processing (matrix geometry) specifies a zero thickness at the edge for each phase element, which can be used as a reference variable, so that the tolerances can only be met over very small areas. By locally separating the phase elements, reference signals for digital holographic processing can also be obtained from the spaces or the zones of the matrix correlator not occupied by phase elements.

The phase difference between adjacent rings in a Newtonian interferometer is λ / 2. In order to achieve interference in a structure with a geometric thickness h, the optical path Δx in the medium of the individual phase elements (refractive index n ₂ ) must meet the interference condition

Δx ≧ 2n ₂ h (1)

(ie at least one revolution is required), where Δx is also linked to the transit time Δt via the speed of light c:

Δx = cΔt (2)

With Eq. ( 1 ) and Eq. ( 2 ) the modified interference condition is obtained for a pulse duration of τ

h ≦ h _int = cτ / ( 2 n ₂ ) (3)

The thickness of the micro-optical phase element must therefore not exceed a maximum value h _int , which is given by the smallest pulse duration τ to be measured [cf. also: SA Akhmanov, VA Vysloukh, AS Chirkin: Optics of Fentosecond Laser Pulses. - American Institute of Physics, New York 1992 , p. 51-53].

On the other hand, the phase shift must be large enough to sufficient at the wavelength λ, at least however, to make two rings appear.

To avoid impulse distortions through the substrate (Dispersion, phase error), the substrate must be on the side facing the detector and one Imaging onto the detector through the substrate respectively.

With a pulse duration of 10 fs (for a chirp-free or chirp-compensated pulse) and a refractive index of n ₂ = 1.7, the thickness of the micro-optics must therefore be approximately <1 µm. At 1 fs, the permissible thickness is reduced to 100 nm, which is still well mastered technologically. In the case of very short pulses, however, the contrast is impaired by the spectral broadening of the pulses (quasi-white light rings), so that spectrally selective components and / or nonlinear interactions must be used to improve the resolution. Additional filtering can also be carried out by using spectral properties of the detector and by suitable image processing algorithms. The errors that occur due to the action of spectrally selective measuring components on the pulse must be compensated.

Interference rings on the entire surface of the individual phase elements are observed for thicknesses h which are smaller than the coherence length of the pulse. At thicknesses h <h _int , interferences occur in those areas that are thinner than h _int , e.g. B. on the edge of a microlens. In order to avoid the resulting measurement uncertainty, a matrix correlator can be used which is constructed from phase elements in such a way that upper parts with the same thickness profiles or the same curvatures are applied to differently high, cylindrical parts of the fuselage.

The phase shift across the surface is thus one Phase element the same, the maximum or  however, minimum thickness varies from phase element to Phase element and can be precisely measured on the Time range can be coordinated.

In the design of the phase elements and the illustration systems, it must be taken into account that the camera Interference rings must resolve. Therefore they are allowed to Single phase elements should not be too small. Advantage a high resolution camera (small Pitches of pixels) with and high dynamic range (e.g. a CMOS camera with logarithmic sensitivity scale) used.

In terms of scaling, the requirement must be that a sufficient number of camera pixels are effective per phase element in order to achieve the required location and time resolution. Assuming a pixel size of 5 microns and a period of 10 microns for the detector, and assuming that 20 × 20 pixels per micro-optical single phase element are required for the resolution of the ring structures, you get with dense packing of the phase elements and at a beam diameter of 2 mm without beam expansion, a number of 10 × 10 = 100 phase elements or steps with a total of 200 × 200 = 40,000 pixels. Expanded to a detector area of 10 × 10 mm ² , 1000 × 1000 = 1 million pixels could be used accordingly, with 100 × 100 pixels being then assigned to each phase element. The imaging optics must be selected so that on the one hand the interference structures are resolved well and no moiré effects occur, on the other hand the depth of field sweeps over the entire effective thickness or phase shift.

With a sufficiently low waviness of the substrate and a good control of the layer thickness could Theoretically, a discrete structure of a multi-channel correlator even through a single coherent macroscopic dimensioned phase element with variable phase be replaced, the expansion of the entire beam covered, but such a quality is in difficult to achieve in practice, and spatial Dissolution would be lost.

With the high dynamic range, oversteer can be achieved Avoid interference from interference peaks that otherwise would have to be compensated optically or electronically. The camera should have a high fill factor, however no integrated microlenses and none thin window (based on the pulse length or Coherence length).

It is useful to avoid impulse distortions moderately, a mirror telescope for beam expansion use. Become a nonlinear overlay either non-linear optical phase elements in the Beam path introduced, the micro-optical elements of the matrix correlator itself or the substrate suitable nonlinear optical materials provides or a detector array from a suitable non-linear optical material used.  

Beam components separated by suitable beam splitters or such beam components, the spaces or Edge areas of the matrix correlator pass or past it can be used as a reference signal for a holographic overlay are used in the the evaluation is done digitally (by computer). Here can use a Fresnel transformation to transform the complex Amplitude distribution in the plane of the real image determined and through further mathematical procedures additional information, e.g. B. on the temporal integrated phase distribution.

A one-dimensional time-resolved phase measurement is possible if a quick deflection (e.g. via Kerr effect) similar to the mode of action more specific Streak cameras in the interference pattern on the camera is deflected in one direction.

With polarized radiation or polarization sensitive components in the optical system (which then act as an analyzer) it should be noted that parasitic Rings can arise when the radiated surfaces Angle too steep, because then micro optics in Location variable depending on angle and layer thickness Have polarization properties.

Disruptive influences of self-imaging effects (Talbot effect), especially with the holographic over storage with beam used as reference beam divide from spaces or marginal areas due to a suitable structure (e.g. illustration at an angle to  optical axis) excluded or filtered out become.

When using imaging micro-optics (e.g. Microlenses) can result from the transverse deflection of their foci also time-integrated (or, with a 1D array of phase elements when using a fast additional deflection device, in one Spatial direction also temporally resolved) information over the wavefront because the matrix Correlator also works as a Shack-Hartmann sensor.

Are transmitting or reflecting objects in introduced the beam that when interacting with the Laser pulse during the pulse changes the Such changes can cause phase distribution either according to the Shack-Hartmann measurement principle detected or holographically using a Reference beam are recorded. If at holo graphic measurement of the phase front through the substrate is affected, corresponding shares in the Evaluation will be deducted.

To make statistically relevant statements about coherence, Pulse duration or phase or (as 1D cuts) via Whole distribution can be maintained Rows and / or columns from identical phase elements be used.

The method and arrangement are distinguished from the State of the art through a long achievable time resolution and a high degree of compactness.

The invention will become more specific below Embodiments shown in more detail. In the associated drawing show:

Fig. 1 is a schematic representation of a multichannel correlator arrangement lator according to the invention with a matrix Tac with individual curve profiles of the phase elements,

Fig. 2 shows the schematic representation of FIG. 1 with phase elements, all having a same radius of curvature,

Fig. 3a shows the schematic representation of FIG. 2 with a beam splitter and

FIG. 3b shows the schematic representation of FIG. 3a with a wave packet as an incident beam.

Embodiment 1

In embodiment 1, as shown in FIG. 1, a multi-channel correlator arrangement according to the invention in which optical interference on a matrix correlator 2 , which is preferably introduced perpendicularly to the optical axis into an incident beam 1 and consists of a matrix, is shown below also referred to as phase elements 3 , micro-optical single-phase elements with preferably individually different local thickness or phase profiles, for time-resolved characterization of ultrashort laser pulses by means of interferometric autocorrelation.

The spatial extension of the beam 1 in the direction of the axis is indicated in FIG. 1 with a wave packet 1 a, which is intended to represent a snapshot picture at a specific point in time.

In this arrangement according to FIG. 1, an inhomogeneous array of thin-film microlenses 3 a is used as the matrix correlator 2 , which are applied to a preferably plane-parallel substrate 4 by photolithographic structuring of lacquer layers or by vapor deposition of dielectric layers. Highly refractive dielectric layers with good adhesion and high laser strength are preferably used. The preferably spherical or parabolic microlenses 3 a are evaporated separately, ie the fill factor is significantly smaller than 1. The individual thickness or phase profiles of the microlenses 3 a used as phase elements each reach the value zero at the edge, the curvature profiles of the phase elements 3 distinguish a from each other.

The substrate thickness is selected so that no interfering interference is generated by the substrate 4 in the relevant time range. The substrate 4 is oriented towards a detector 7 , has one of the phase elements 3 a, here the microlenses, various, preferably lower refractive index and can be broadband anti-reflective on the back. The interference rings 5 generated by linear interference in the phase elements 3 a are imaged by means of imaging optics (preferably microscope objective) 6 on the detector 7 , preferably a CMOS matrix camera of high pixel density with a high dynamic range, and evaluated on a computer with regard to their contrast distribution and provide statements about the coherence length (phase coherence) of the laser pulses, in the case of chirp-free pulses also the pulse duration. The ring spacings of the interference rings 5 are not equidistant due to the shape of the lens.

A spectral filter 11 can be connected upstream of the detector 7 , which must have a sufficiently high thickness in order not to produce parasitic interference.

Embodiment 2

In the exemplary embodiment 2 according to FIG. 2, a multi-channel correlator arrangement is similar to that described in exemplary embodiment 1 , wherein instead of the thickness or phase profiles of the individual phase elements 3 b of the matrix correlator 2 falling to zero at the edge in those used here Phase elements 3 b at the edge a value different from zero and different from phase element 3 b to phase element 3 b is achieved. The curvature profiles of all phase elements 3 b among themselves are the same. The thickness or phase steps of the phase elements 3 b are realized here by supporting parts 14 of different thicknesses, on which the same thick and equally curved lens upper parts 15 are seated.

Embodiment 3

In the embodiment 3 according to the representation in FIGS . 3a and 3b, similar multi-channel correlator arrangements are constructed as in embodiment 2. The optical system is first with a well-defined phase distribution, preferably one generated with a cw laser, in good approximation flat shaft 1 e calibrated ( Fig. 3a). This shaft 1 e is split into a reference portion, the planar reference wave K1, which is separated by a suitable beam splitter 12 or from non-irradiated areas of the matrix-correlator 2, and having passed through the matrix-correlator 2 imaged and the detector 7 Share, the transmitted plane wave 1 te, which carries the phase information of the phase elements 3 b and the substrate 4 . Both components 1 re and 1 te are superimposed on the detector 7 , for which purpose a deflection mirror 13 is used in the exemplary embodiment, and generate a reference hologram which is recorded and stored. In the actual measurements with ultrashort pulses ( FIG. 3b) in single-pulse operation, parts of the radiation which are not propagated by the matrix correlator 2 are then used as the reference portion of the laser wave 1 rl and with the transmitted laser wave 1 tl, which is both the phase information of the matrix correlator 2 including substrate 4 as well as that of the incident laser wave 1 is superimposed on the detector 7 , whereby a measurement hologram is generated. Information about the time-averaged spatial phase distribution is then obtained by comparing the measurement hologram and reference hologram. If a phase object (not shown) is additionally brought into the beam path in front of the matrix correlator 2 , the phase distribution of which changes during the laser pulse, its time-averaged phase change can also be determined using the same calibration procedure.

Embodiment 4

Embodiment 4 (not shown) is constructed similarly to Embodiment 2, except that nonlinear-optical phase elements are used which consist of a suitable material with non-linear-optical properties. There is a nonlinear overlay, in which the temporal intensity curve for individual laser pulses can be inferred from the local distribution and contrast of the interference rings 5 ( FIG. 1).

Embodiment 5

Embodiment 5 (not shown) is constructed similarly to embodiment 2, the micro-optical phase elements consisting of cuboids or cylinders of different heights, each with the same pyramids or cones. Instead of the non-equidistant rings 5 ( FIG. 1), corresponding concentric, square or circular, equidistant stripe patterns are created. The angles of inclination of the top surfaces of the phase elements with respect to the substrate are chosen so that no total reflection occurs in the phase elements.

Embodiment 6

Embodiment 6 (not shown) is constructed similarly to embodiment 2, the detector 7 ( FIG. 1) being preceded by a linear optical processor, preferably a 4-f system composed of microlens arrays with an integrated filter level. By filtering out essential features of the interference patterns in real time, the image processing is improved and accelerated.

Embodiment 7

Embodiment 7 (not shown) is constructed similarly to embodiment 2, with a dispersive grating connected upstream of the detector 7 ( FIG. 1).

Embodiment 8

Embodiment 8 (not shown) is constructed similarly to embodiment 2, with the phase elements 3 and thus the matrix correlator 2 ( FIG. 1) being applied directly in front of the pixels of the camera without an imaging system.

Embodiment 9

Embodiment 9 (not shown) is similar constructed as the embodiments 3 and 4, wherein a holographic overlay with a reference do not radiate (as in embodiment 3) on the Detector, but in the from a suitable not linear optical material existing phase elements takes place, thus as a non-linear holographic Serve recording medium.

Embodiment 10

Embodiment 10 (not shown) is constructed similarly to embodiment 1, with an electrically addressable spatial light modulator (spatial light modulator, SLM) with controllable phase of the individual elements serving as matrix correlator 2 ( FIG. 1).

Reference list

1

incident beam

1

a wave packet

1

re flat reference wave

1

te transmitted reference wave

1

rl reference portion of the laser wave

1

t1 transmitted laser wave

2nd

Matrix correlator

3rd

Phase elements

3rd

a phase elements with different curvature

3rd

b Phase elements with the same curvature

4th

Substrate

5

Interference rings

6

Imaging optics

7

detector

8th

Lower part

9

Lens top

10th

11

Spectral filter

12th

Beam splitter

13

Deflecting mirror

Claims (26)

1. A method for the time-resolved characterization of ultrashort laser pulses using a multi-channel correlator technique, in which an interferometric overlay of parts of the beam ( 1 ) with itself in a matrix ( 2 ) of phase elements ( 3 a, 3 b) on one transmitting substrate ( 4 ), which have a different refractive index from the refractive index of the substrate ( 4 ), by utilizing the internal reflection in the phase elements ( 3 a, 3 b) and the Fabry-Perot effect which can be achieved in such a way that Characteristic inter interference patterns such as rings ( 5 ) are generated, the phase elements ( 3 a, 3 b) or different groups of phase elements ( 3 a, 3 b) each have different phase profiles and thus the pulse is tested simultaneously in corresponding channels for interference capability , after imaging the interference pattern on a detector designed as a matrix camera ( 7 ) an electro African and / or mathematical processing of the interference pattern takes place and in this way information about the coherence length or about the temporal and spatial intensity curve can be obtained. 2. The method according to claim 1, characterized in that on the detector ( 7 ) or in a suitable medium, a holographic overlay of a separated by means of a beam splitter ( 12 ) and the phase elements ( 3 a, 3 b) non-continuous part of the laser beam ( 1 ), which serves as a reference beam ( 1 right ), with which the interference pattern occurring in the phase elements ( 3 a, 3 b) takes place and information about the spatial distribution of the wave field is obtained from the detected intensity distribution by comparison with reference holograms using suitable mathematical procedures. 3. The method according to claim 1 or 2, characterized in that the phase elements ( 3 a, 3 b) are oriented towards the incident beam ( 1 ). 4. The method according to any one of claims 1 to 3, characterized in that phase elements ( 3 b) of the same curvature are used. 5. The method according to any one of claims 1 to 4, characterized in that Phase elements with planes irradiated Subareas and preferably prismatic or Pyramid shape are used, the Inclination angle of the partial surfaces in relation to the Substrate surface should be chosen so that none Total reflection occurs. 6. The method according to any one of claims 1 to 5, characterized in that the detector ( 7 ) additionally spectrally selective components such as gratings are connected upstream. 7. The method according to any one of claims 1 to 6, characterized in that the detector ( 7 ) is connected upstream of a linear optical processor, so that real-time image filtering is carried out and thus an improvement in the detection of essential features of the interferometric or holographically generated intensity pattern is achieved becomes. 8. The method according to any one of claims 1 to 7, characterized in that the phase elements ( 3 ) or the substrate ( 4 ) carrying them or a separate optical component in front of the detector ( 7 ) or the detector ( 7 ) itself are selected such that they have non-linear optical properties and the temporal intensity curve is detected optically or electrically from the interference patterns via multiphoton processes. 9. The method according to claim 8, characterized in that the interferometric overlay in one suitable nonlinear medium carried out in this way is that a two- Photon fluorescence is excited. 10. The method according to claim 8, characterized in that the interferometric overlay in one suitable nonlinear medium carried out in this way is that the second signal  Harmonic (SHG) of the laser radiation is excited. 11. The method according to any one of claims 1 to 10, characterized in that for transient recording of the interference pattern a photorefractive medium is used. 12. The method according to any one of claims 1 to 11, characterized in that a spatial light modulator is used as the matrix ( 2 ), the individual elements of which have a controllable phase. 13. Arrangement for the time-resolved characterization of ultrashort laser pulses using a multi-channel correlator technique, in which in the laser beam path ( 1 ) a matrix of phase elements ( 3 ) on a transmitting substrate ( 4 ) with a different from the refractive index of the phase elements ( 3 ) Refractive index is introduced, the parts of the beam ( 1 ) by utilizing the internal reflection in the phase elements ( 3 ) and the Fabry-Perot effect that can be achieved with it brings about the interferometric superposition with itself, so that characteristic interference patterns such as rings ( 5 ) are generated , whereby the phase elements ( 3 ) or different groups of phase elements ( 3 ) each have different phase profiles, a suitable optical system ( 6 , 11 ) is arranged between the matrix of phase elements ( 3 ) and a detector ( 7 ) designed as a matrix camera that the interference pattern on the detector ( 7 ) map t and are then processed electronically and / or mathematically via a processing device connected to the detector ( 7 ) to provide information about the coherence length or about the temporal and spatial intensity curve. 14. Arrangement according to claim 13, characterized in that a beam splitter ( 12 ) is arranged which separates a part of the incident beam ( 1 ) as a reference beam ( 1 re), which outside the phase elements ( 3 ) as a reference beam ( 1 re) and with the interference pattern generated in the phase elements ( 3 ) to be superimposed on the detector ( 7 ), a comparison being made with reference holograms and information about the spatial distribution of the wave field as well as the phase distribution from the detected intensity distribution using suitable mathematical procedures of the laser. 15. The arrangement according to claim 13 or 14, characterized in that the phase elements ( 3 ) are oriented towards the incident beam ( 1 ). 16. Arrangement according to one of claims 13 to 15, characterized in that the phase elements ( 3 b) have the same curvature. 17. Arrangement according to one of claims 13 to 16, characterized in that the phase elements ( 3 ) plane planar partial areas and have a prismatic or a pyramid shape, wherein the angle of inclination of the partial areas relative to the substrate surface ensure that no total reflection occurs. 18. Arrangement according to one of claims 13 to 17, characterized in that additionally spectrally selective components such as optical gratings are arranged in front of the detector ( 7 ). 19. Arrangement according to one of claims 13 to 17, characterized in that a suitable microlens array is arranged as imaging optics ( 6 ). 20. Arrangement according to claim 19, characterized in that a microlens is assigned to each phase element. 21. Arrangement according to one of claims 13 to 18, characterized in that a linear optical processor is arranged between the matrix ( 2 ) and the detector ( 7 ), so that real-time image filtering is carried out and thus an improvement in the detection of essential features of the intensity pattern generated interferometrically or holographically is achieved. 22. Arrangement according to one of claims 13 to 21, characterized in that the phase elements ( 3 ) or a substrate ( 4 ) carrying them or a separate optical component in front of the detector ( 7 ) or the detector ( 7 ) itself nonlinear-optical properties have and the interference pattern of the temporal intensity course is optically or electrically detected via multi-photon processes. 23. Arrangement according to claim 22, characterized in that the interferometric overlay in one suitable nonlinear medium takes place in such a way that a two-photon Fluorescence arises. 24. Arrangement according to claim 22, characterized in that the interferometric overlay in one suitable nonlinear medium takes place in such a way that the second harmonic as an evaluable signal (SHG) of the laser radiation. 25. Arrangement according to one of claims 13 to 22, characterized in that for transient recording of the interference pattern a photorefractive medium is used. 26. Arrangement according to one of claims 13 to 16, characterized in that a spatial light modulator is used as the matrix ( 2 ), the individual elements of which have a controllable phase.