AT527337A1 - Device and method for manipulating pulsed laser radiation - Google Patents

Abstract

Method for manipulating pulsed laser radiation (2), comprising the steps of: - providing pulsed laser radiation (2); - spatially separating the frequency components of the pulsed laser radiation (2) to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation (2); - guiding the pulsed laser radiation (2) spatially separated to the first predetermined extent to a multiple-pass gas cell (8); - increasing the spectral bandwidth of the pulsed laser radiation (2) in the multiple-pass gas cell (8) for temporal pulse compression of the pulsed laser radiation (2). Furthermore, a corresponding device (1).

Description

The invention relates to a device and a method for

Manipulating pulsed laser radiation.

Over the last two decades, hollow core fibers (HCF) have been used for pulse compression because they provide spectral broadening and have a waveguide geometry that allows the length of the nonlinear optical interaction to be extended to several meters with negligible dispersion. However, multipass gas cells (MPCs) have emerged as a practical alternative to HCFs to provide spectral broadening by self-phase modulation (SPM) in gases. Compared to HCFs, MPCs offer more compact setups and less demanding constraints on beam alignment stability. Nevertheless, both solutions suffer from unfavorable spatial scaling of the setup.

structures when pulses with higher energies are treated.

External pulse compression using MPC is an extremely powerful technique to shorten the duration of sub-ps laser pulses (see M. Hanna, X. Delen, L. Lavenu, F. Guichard, Y. Zaouter, F. Druon, and Patrick Georges, "Nonlinear temporal compression in multipass cells: theory" J. Opt. Soc. Am. B 34, 1340-1347 (2017)). Despite its enormous success and versatility, the MPC method faces the challenge of dealing with high energy because of unfavorable geometric scaling requiring a rapid increase in the distance between the concave mirrors and the corresponding size of the vacuum chamber.

Two material parameters - the ionization threshold of the gas used as self-phase modulation (SPM) medium (typically Ar for higher pulse energies) and the destruction threshold of the dielectric coating on the cell mirrors - determine the length scaling of the MPC as a function of the pulse energy. While the strength of the SPM can be controlled by adjusting the noble gas pressure, this does not apply to the plasma losses. The latter can only be suppressed by a sufficiently large beam waist to keep the peak intensity of the pulse at a safely low level. Due to the loose fo-

cussing requires a long propagation distance to the mirror.

necessary to increase the beam size and reduce the fluence to a safe level, which is -0.5-0.6 J/cm2* for sub-ps pulses with the currently available coatings. In M. Kaumanns, D. Kormin, T. Nubbemeyer, V. Pervak, and S. Karsch, "Spectral broadening of 112 mJ, 1.3 ps pulses at 5 kHz in a LG10 multipass cell with compressibility to 37 fs" Opt. Lett. 46, 929-932 (2021), an attempt was made to reduce the fluence by converting the fundamental spatial mode of the laser beam into a higher order mode that has a significant

enables a significantly larger spot size.

MPCs are therefore limited in terms of pulse energy and the corresponding pulse intensity due to the destruction threshold of the optics and the ionization limit of the gas in the cell. Consequently, the energy scaling of the laser pulses also requires a spatial scaling of the MPC, i.e. larger MPCs are required for higher pulse energies.

The object of the invention is to alleviate or eliminate one or more of the disadvantages of the prior art. In particular, the object of the invention is to propose a device and a method for providing pulsed laser radiation, preferably for pulse compression, in particular for the amplification of chirped pulses (Chirped Pulse Amplification, CPA) and/or for CPA, which allow higher pulse energies.

and/or allow a smaller size of the MPC.

This is achieved by a method for manipulating pulsed laser radiation comprising the steps:

- Providing pulsed laser radiation;

- spatially separating the frequency components of the pulsed laser radiation to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation;

- guiding the pulsed laser radiation spatially separated to the first predetermined extent to a multi-pass gas cell;

- Increasing the spectral bandwidth of the pulsed laser radiation in the multi-pass gas cell for temporal pulse

compression of the pulsed laser radiation.

- a device for providing pulsed laser radiation;

- a separation element for spatially separating the frequencies of the pulsed laser radiation to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation;

- a multiple-pass gas cell for increasing the spectral bandwidth of the pulsed laser radiation for temporal pulse compression of the pulsed laser radiation, wherein the multiple-pass cell is arranged in the optical path of the pulsed laser radiation

is arranged behind the separation element.

When the energy of the laser pulse is increased, the intensity in the laser focus exceeds the threshold of the optimal range. To avoid the increase in intensity with a simultaneous increase in energy, it is necessary to increase the size of the laser focus. I=E/ (A*7),

with I=intensity, E=laser pulse energy, A=area of the laser focus, i=laser pulse duration. The size of the laser focus r [r « f/a, r=radius of the laser focus, f=distance of the focus, a=radius of the laser spot on the mirror] can be increased in the MPC:

- by reducing the size (a) of the laser on the mirrors => limited by laser damage on the mirrors

- by increasing the distance (£f) between the mirrors and the focus => limited by the restrictions for the maximum

times the permissible size of the MPC.

By spatially separating the beam before feeding it to the multi-pass gas cell, the size of the collimated beam in the multi-pass gas cell (especially at the mirrors of the multi-pass gas cell) is increased. At the same time, the size of the beam in focus is maintained. It is noteworthy that the intensity on the mirrors decreases even faster than the fluence, since the effective pulse duration on the mirrors changes due to the monochromatizing effect of spatial chirping.

This is important in that the damage

duction mechanism advantageously changes from an avalanche-dominated effect (for fs pulses) to a thermally dominated effect (>>ps), which enables the use of higher fluences. The pulse duration of the collimated beam is thus increased, whereas the original pulse duration is restored when the beam is focused. As a result, it is possible to increase the laser energy in the optics without changing the properties of the laser pulse (duration) and the beam (spot size) at the focus, where the desired spectral bandwidth increase normally takes place. By reducing the fluence on the optical elements of the multi-pass gas cell, the maximum pulse energy limit is increased, for example, by a factor of between 1.4 and 2 for a fixed length of the multi-pass gas cell. For a fixed pulse energy, the length of the multi-pass gas cell can be increased, for example, by a factor of 1.4 to 2

be reduced.

Temporal broadening is understood to mean temporal stretching of the frequency components, i.e. the introduction of a temporal chirp (used synonymously with spectral chirp). Temporal broadening refers to the reverse process of temporal compression. Spatial separation is understood to mean the introduction of a spatial chirp. Diffraction into different angles is understood to mean the introduction of an angular chirp. Preferably, the spatial separation of the frequency components of the pulsed laser radiation is not reversed in the first predetermined extent before the pulsed laser radiation is guided to the MPC. Preferably, the pulsed laser radiation is broadened when injected into the MPC compared to the originally provided pulsed laser radiation by the factor by which the pulsed laser radiation was broadened during spatial separation in the first predetermined extent.

was widened to a considerable extent.

The multiple-pass gas cell is in particular filled with a filling gas, for example argon, which has an optical non-linearity. The multiple-pass gas cell contains in particular a medium with non-linear optical properties in which the pulsed laser radiation is given a non-linear phase by self-phase modulation. The MPC preferably has at least

at least two mirror elements between which the pulsed charge

radiation is reflected several times. In particular, the multiple-pass gas cell has two opposing mirrors that form a concentric resonator through which the pulsed laser radiation passes several times. Preferably, the non-linear medium, in particular argon, is provided between the mirrors. Of course, several non-linear elements can also be arranged as a non-linear medium between the mirrors. The pulsed laser radiation is injected in particular into the multiple-pass cell. The MPC preferably has two spherical mirrors, in particular those with low

ger dispersion (e.g. Optoman).

Preferably, the device has a laser radiation source for providing the pulsed laser radiation. The pulsed laser radiation is in particular ultrashort pulse sequences. The pulsed laser radiation (originally provided (i.e. before carrying out the remaining steps of the method), in particular by the laser radiation source) comprises laser pulses with pulse energies in the range of 0.5 mJ to 25 mJ, preferably 1 mJ to 14 mJ, in particular 2.5 mJ, and pulse durations in the range of 10 fs

to 5 ps, preferably 100 £fs to 500 fs, especially from 250 fs.

The extent of the broadening refers in particular to the factor between the beam waist before the broadening and after the broadening (in the direction perpendicular to the direction of propagation). It is advantageous if, during spatial separation of the frequency components of the pulsed laser radiation in the first predetermined extent, a broadening of the pulsed laser radiation in the direction perpendicular to the direction of propagation of the pulsed laser radiation takes place to at least 1.5 times, preferably at least twice, particularly preferably at least 3 times.

Preferably, the method comprises the following step, which is performed before increasing the spectral bandwidth of the pulsed laser radiation in the multi-pass gas cell (and before directing the pulsed laser radiation spatially separated to the first predetermined extent to a multi-pass gas cell):

- temporal pulse compression (of the frequency components) of the

pulsed laser radiation in a dispersion arrangement which has at least two dispersive elements, in particular optical gratings, which are designed to spatially separate the frequency components of the pulsed laser radiation by a second predetermined amount and, after propagation over an optical path length which differs depending on the frequency, to combine the frequency components of the pulsed laser radiation according to the second amount, so that a temporal pulse compression of the pulsed laser radiation is effected. This can be a temporal pulse compression as carried out in CPA. Preferably, a collimated, laterally expanded (broadened) beam is obtained by breaking the symmetry between an incoming and an outgoing pass through the dispersion arrangement, in particular the at least two dispersive elements. It is advantageous if, during spatial separation of the frequency components of the pulsed laser radiation to the second predetermined extent, the pulsed laser radiation is widened in the direction perpendicular to the direction of propagation of the pulsed laser radiation to at least 1.5 times, preferably at least twice, particularly preferably at least 3 times. Preferably, during spatial merging, at least a corresponding narrowing occurs. It is advantageous if, during spatial merging of the frequency components of the pulsed laser radiation to the second predetermined extent, the pulsed laser radiation is narrowed in the direction perpendicular to the direction of propagation of the pulsed laser radiation to equal to or less than 2/3 times, preferably equal to or less than half, particularly preferably equal to or less than 1/3 times. In particular, during spatial merging of the frequency components of the pulsed laser radiation to the second predetermined extent, the original spot size and the original overlap of the different frequency components are restored.

It is advantageous if

for spatially separating the frequency components of the pulsed laser radiation by the second predetermined amount with a first of the at least two dispersive elements, the frequency components

the pulsed laser radiation is diffracted into different angles

and with a second of the at least two dispersive elements the frequency components of the pulsed laser radiation diffracted at different angles are collimated; and

for spatially combining the frequency components of the pulsed laser radiation according to the second dimension, the frequency components of the pulsed laser radiation are diffracted into different angles with the second of the at least two dispersive elements and the frequency components of the pulsed laser radiation diffracted into different angles are collimated with the first of the at least two dispersive elements. The dispersion arrangement can comprise a Treacy pair compressor (if necessary additionally

with a separation element, see below).

It is advantageous if the spatial separation of the frequency components of the pulsed laser radiation takes place to the first predetermined extent in the direction perpendicular to the direction of propagation of the pulsed laser radiation in that a first optical path length of the pulsed laser radiation between the first of the at least two dispersive elements and the second of the at least two dispersive elements during spatial separation of the frequency components of the pulsed laser radiation differs by the second predetermined extent from a second optical path length of the pulsed laser radiation between the second of the at least two dispersive elements and the first of the at least two dispersive elements during spatial merging of the frequency components of the pulsed laser radiation according to the second extent. This allows a controlled extent

a spatial chirp can be introduced into the resulting beam.

It is preferred if the spatial separation of the frequency components of the pulsed laser radiation to the first predetermined extent in the direction perpendicular to the direction of propagation of the pulsed laser radiation is effected during the temporal pulse compression of the pulsed laser radiation with a separation element in the dispersion arrangement. Advantageously, the already available dispersive elements can thus be used to achieve the spatial chirp to the first extent. Preferably, the spatial separation to the first extent (in contrast to the spatial separation to the second extent, which the

temporal pulse compression) not the other way round. The separati-

onselement causes in particular the above-described un-

difference in the optical path length.

It is preferred if the pulsed laser radiation is reflected in the dispersion arrangement with a mirror, wherein the pulsed laser radiation is propagated in the dispersion arrangement (from an input of the dispersion order) along a first optical path to the mirror and, after reflection at the mirror, is propagated along a second optical path (to an output of the dispersion order), wherein the at least two dispersive elements are located in the first optical path and in the second optical path, wherein the separation element is only in the

first optical path or only in the second optical path.

It is advantageous if the separation element has four mirrors. This makes it easy to achieve a controlled

degree of spatial chirp can be achieved.

Preferably, the method is a method for CPA. Preferably, the method further comprises the following steps, which are carried out before spatially separating the frequency components of the pulsed laser radiation to the first predetermined extent:

- temporal broadening/stretching of the pulsed laser radiation (preferably to the inverse extent of the temporal pulse compression with the dispersion arrangement) +;

- Amplification of the temporally broadened pulsed laser

radiation.

With reference to the device, it is advantageous if it has a dispersion arrangement, preferably a grating pair pulse compressor, in particular a Treacy pair pulse compressor, for temporal pulse compression of the pulsed laser radiation with at least two dispersive elements, in particular optical gratings. The dispersive elements are in particular designed to spatially separate the frequency components of the pulsed laser radiation by a second predetermined amount and, after propagation over a frequency-dependently different optical path length, to combine the

Frequency components of the pulsed laser radiation according to the

second extent, so that a temporal pulse compression of the pulsed laser radiation is effected. The dispersive elements are in particular designed so that, in order to spatially separate the frequency components of the pulsed laser radiation by the second predetermined extent, the frequency components of the pulsed laser radiation are diffracted into different angles with a first of the at least two dispersive elements and the frequency components of the pulsed laser radiation diffracted into different angles are collimated with a second of the at least two dispersive elements; and

for spatially combining the frequency components of the pulsed laser radiation according to the second extent, the frequency components of the pulsed laser radiation are diffracted into different angles with the second of the at least two dispersive elements and the frequency components diffracted into different angles with the first of the at least two dispersive elements

le of the pulsed laser radiation are collimated.

It is advantageous if the dispersion arrangement has a mirror which is arranged so that the pulsed laser radiation in the dispersion arrangement is propagated along a first optical path to the mirror and, after reflection at the mirror, is propagated along a second optical path, wherein the at least two dispersive elements are located in the first optical path and in the second optical path, wherein the separation element is only in the first optical path or only in the second optical path

is intended.

It is preferred if the separation device has four mirrors, which in particular extend the optical path

achieve.

It is advantageous if the device comprises:

- a broadening device for temporally broadening the pulsed laser radiation;

- an amplification device for amplifying the temporally broadened pulsed laser radiation;

wherein the separation element and the multi-pass cell are arranged in the optical path of the pulsed laser radiation after propagation

amplification device and the reinforcement device

The amplification device may comprise one or more

levels of strength.

The device for providing pulsed laser radiation can comprise a laser beam source. Preferably, the device for providing pulsed laser radiation comprises: the laser beam source, the broadening device, the amplification device and optionally the dispersion arrangement. The MPC preferably serves as a post-compressor. Advantageously, the post-compression effect (i.e. the spectral broadening) occurs mainly

mainly in the laser focus in the center of the post-compressor.

Fig. 1 shows schematically a preferred embodiment of a

Device for manipulating pulsed laser radiation.

Fig. 2 shows schematically a preferred embodiment of a

known dispersion arrangement.

Fig. 3 shows schematically a preferred embodiment of a dispersion arrangement of the device for manipulating

pulsed laser radiation, with a separation element.

Fig. 4 shows schematically a preferred embodiment of a multi-pass gas cell of the device for manipulating

pulsed laser radiation.

Fig. 5 shows the fluence and the beam waist depending on the

extent of spatial separation.

Fig. 6a shows the peak power and Fig. 6b the spot size at

Path to Focus.

Fig. 7a shows normalized intensity as a function of wavelength and Fig. 7b the normalized intensity as a function of

on the pulse duration.

Fig. 1 shows schematically a preferred embodiment of a device 1 for manipulating pulsed laser radiation 2. In this embodiment, the device 1 is used for CPA.

The device 1 has a device 3 for providing

set up pulsed laser radiation 2, in particular a laser beam source. The pulsed laser radiation 2 is guided to a widening device 4 for temporally stretching the pulsed laser radiation 2. The temporally widened laser radiation 2 is amplified in an amplification device 5. The temporal pulse compression of the amplified pulsed laser radiation 2 takes place in a dispersion arrangement 6. The dispersion arrangement 6 also has a separation element 7 for spatially separating the frequencies of the pulsed laser radiation 2 to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation 2. Alternatively, the separation element 7 can be provided independently (outside) of the dispersion arrangement 6. The (again) temporally compressed, spatially broadened pulsed laser radiation 2 is guided to a multiple-pass gas cell 8, which is designed to increase the spectral bandwidth of the pulsed laser radiation 2 for the (further) temporal pulse compression of the pulsed laser radiation 2. The spatial broadening in the first degree increases the size of the collimated beam in the multiple-pass gas cell 8. At the same time, the size of the beam in the focus of the MPC 8 is maintained. The pulse duration of the collimated beam is increased, whereas the original pulse duration is restored when the beam is focused. As a result, it is thus possible to increase the laser energy in the optics without changing the properties of the laser pulse (duration) and the

beam (spot size) in focus.

The device 1 can also comprise only the device 3 for providing the pulsed laser radiation 2, the separation element

element 7 and the multi-pass gas cell 8.

Fig. 2 shows schematically a preferred embodiment of a

known dispersion arrangement 6, which is also used in the device 1 for manipulating pulsed laser radiation 2

can occur (this is particularly preferred if the dispersion arrangement 6 and the separation element 7 are designed separately). In this embodiment, the dispersion arrangement 6 is in particular a Treacy pair pulse compressor. The dispersion arrangement

Order 6 has an entrance mirror IM and a middle mirror.

RM and an output mirror OM. An upper level of the dispersion arrangement 6, which represents a first optical path 9 of the pulsed laser radiation 2 in the dispersion arrangement 6 from the input mirror IM to the center mirror RM, is shown in part figure (a). A lower level of the dispersion arrangement 6, which represents a second optical path 10 of the pulsed laser radiation 2 in the dispersion arrangement 6 from the center mirror RM to the output

The image representing the input mirror OM is shown in sub-figure (b).

The dispersion arrangement 6 has a first optical grating G1 and a second optical grating G2, both of which lie in the first optical path 9 and the second optical path 10. The pulsed laser radiation 2 is coupled into the dispersion arrangement via the input mirror IM. The first optical grating G1 causes the frequency components of the pulsed laser radiation 2 to be fanned out at different angles (angular chirp). As an example, two frequency components of the pulsed laser radiation 2 are shown in Fig. 2, namely an exemplary low-frequency (e.g. red) frequency component as a dashed line 2a and an exemplary high-frequency (e.g. blue) frequency component 2b as a dotted line. The second optical grating G2 causes the frequency components of the pulsed laser radiation 2 to be fanned out in exactly the opposite direction (angular chirp), so that the pulsed laser radiation 2 is collimated again. The pulsed laser radiation 2 is then reflected back at the center mirror RM and then runs along the second optical path 10 in the lower plane of the dispersion arrangement 6. This means that in total the two optical gratings Gl, G2 in the first optical path 9 cause a spatial separation of the frequency components of the pulsed laser radiation 2 by a

second predetermined extent (spatial chirp).

In the second optical path 10, the second optical grating G2 and the first optical grating Gl act in exactly the opposite way to the first optical path 9. This means that the second optical grating G2 causes the frequency components of the pulsed laser radiation 2 to be fanned out at different angles (angular chirp). The first optical grating Gl causes the frequency components of the pulsed laser radiation 2 to be fanned out in exactly the opposite way (angular chirp).

gular chirp), so that the pulsed laser radiation 2 collides again

At the same time, the second optical grating G2 and the first optical grating Gl bring about a merging of the frequency components of the pulsed laser radiation 2 according to the second extent, so that the spatial chirp is cancelled again. Since the frequency components 2 of the pulsed laser radiation travel different optical path lengths, a temporal chirp is thus caused or cancelled, in particular a temporal pulse compression is caused. At the output mirror OM,

the pulsed laser radiation 2 the dispersion arrangement 6.

Fig. 3 shows schematically a preferred embodiment of a dispersion arrangement 6 of the device 1 for manipulating pulsed laser radiation 2. The spatial separation of the frequency components of the pulsed laser radiation 2 to the first predetermined extent in the direction perpendicular to the propagation effect of the pulsed laser radiation 2 during the temporal pulse compression of the pulsed laser radiation 2 is brought about with a separation element 7 that is provided in the dispersion arrangement 6. Otherwise (i.e. apart from the separation element), the dispersion arrangement is designed as described in connection with Fig. 2, so that the same reference numerals as in Fig. 2 are used and reference is made to the above description. The spatial separation to the first extent is brought about by breaking the symmetry between the incoming beam (first optical path 9) and the outgoing beam (second optical path 10). For this purpose, the separation element 7 is only provided in the first optical path, but not in the second optical path. While the first optical grating G1 and the second optical grating G2 in the first optical path 9 bring about a spatial separation to the second extent, and the second optical grating G2 and the first optical grating Gl in the second optical path 10 bring about a spatial merging of the frequency components to the second extent, the separation element 7 brings about a spatial separation to the first extent. The fact that the separation element 7 is only provided in the first optical path 9 does not reverse the spatial separation to the first extent, so that the pulsed laser radiation 2 leaving the dispersion arrangement 6 is also spatially separated to the second extent.

is (spatial chirpgp).

In particular, the separation element 7 is provided between the first optical grating G1 and the second optical grating G2 in the first optical path 9, and there causes an extension of the path length between the first optical G1 and the second optical grating G2 compared to the path length between the second optical grating G2 and the first optical grating G1 in the second optical path 10. As a result, the spatial chirp caused in the first optical path 9 is not completely reversed in the second optical path 10 (but only to the second extent), so that the resulting pulsed laser radiation 2 has a spatial chirp to the first extent when leaving the dispersion arrangement 6 at the output mirror OM, as can be seen from the distance between the two exemplary frequency components 2a, 2b (dotted and dashed line). To extend the path length, the separation element 7 has four mirrors M1, M2, M3, M4.

Fig. 4 shows schematically a preferred embodiment of a multiple-pass gas cell 8 of the device 1 for manipulating pulsed laser radiation 2. The pulsed laser radiation 2, after it has been spatially broadened to the first extent, is focused with a mirror 11 and injected into the multiple-pass gas cell 8. The multiple-pass gas cell 8 has two opposing mirrors CM11, CM2, which form a concentric resonator through which the pulsed laser radiation 2 passes several times. As can be seen, the size of the beam is maintained in the focus. This means that a round beam is present in the focus, whereas the beam spots on the mirrors CM1, CM2 are elongated.

In connection with Figures 4 to 7b, the values achieved by an exemplary embodiment of the method according to the invention or the device according to the invention are shown. Specifically, Fig. 5 shows the fluence and the beam waist as a function of the extent of the spatial separation; Fig. 6a shows the peak power and Fig. 6b the spot size on the way to the focus; Fig. 7a shows standardized intensity as a function of the wavelength and Fig. 7b the standardized intensity as a function of

on the pulse duration.

A Yb CPA grating compressor (as shown in Fig. 3) with a 4-mirror bypass was used to introduce the spatial chirp and the spatially broadened beam was injected into a standard MPC containing two r=-300 low-dispersion spherical mirrors (Optoman) spaced 590 mm apart. As shown in Fig. 4, the 1-D beam spot extension is periodically repeated through the 2£f-2f imaging condition so that the output plane of the spatial chirp is not tilted. This flexible adjustment of the spot size allows easy control of the fluence (cf. Fig. 5) on the mirror while maintaining the peak intensity in the beam waist (Figs. 6a, 6b).

In Fig. 5, the reduction of the peak fluence on the mirrors CM1l, CM2 is particularly evident. Fig. 7a shows in particular the experimental SPM broadening of 2.5 mJ pulses in 1 bar Ar and Fig. 7b the Fourier limit of the pulse. The spectral

and temporal input intensities are shown.

Notably, the intensity on mirrors CM1, CM2 decreases even faster than the fluence, as the effective pulse duration for the coating of mirrors CM1, CM2 changes due to the monochromatizing effect of spatial chirping. This is significant as the damage mechanism changes from an avalanche-dominated effect (for fs pulses) to a thermally dominated effect (for >>ps pulses), allowing the use of higher fluences. Fig. 7a and 7b show our experimentally determined spectral broadening of 2.5-mJ 250-fs pulses that were spatially chirped to stretch the beam spot by -x2, which was the maximum expansion technically possible by the aperture of the laser used in the setup.

installed optics was limited.

Note that the spatial chirp remaining in the beam after spectral broadening and pulse recompression is not critical in many applications. Focusing converts the spatial chirp into an angular chirp, allowing the development of a phase-matched bandwidth during frequency conversion (cf. B.A. Richman, S.E. Bisson, R. Trebino, M.G. Mitchell, E. Sidick, and A. Jacobson. "Achromatic phase-matching in the beam".

tunable second harmonic generation using a grating" Opt. Lett. 22, 1223-1225 (1997)) and wavefront manipulation (H. Vincenti, and F. Quere, "Attosecond lighthouse: how to use spatiotemporally coupled light fields to generate isolated as pulses" Phys. Rev. Lett. 108, 113904 (2012)), while for processes such as higher-order harmonic generation in a gas cell, which is confined to a tiny fraction of the Rayleigh length of the driver beam, both the angular and spatial chirp are controlled within the short inner-

interaction distance can be canceled.

Claims (14)

Patent claims: 1. Method for manipulating pulsed laser radiation (2) comprising the steps: - Providing pulsed laser radiation (2); - spatially separating the frequency components of the pulsed laser radiation (2) to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation (2); - guiding the pulsed laser radiation (2) spatially separated to the first predetermined extent to a multiple-pass gas cell (8); - Increasing the spectral bandwidth of the pulsed laser radiation (2) in the multiple pass gas cell (8) for temporal pulse compression of the pulsed laser radiation (2). 2. Method according to claim 1, wherein during spatial separation of the frequency components of the pulsed laser radiation (2) in the first predetermined extent, a broadening of the pulsed laser radiation (2) in the direction perpendicular to the direction of propagation of the pulsed laser radiation (2) to at least 1.5 times, preferably at least twice, particularly preferably at least 3 times. 3. Method according to one of the preceding claims, comprising the following step, which is carried out before increasing the spectral bandwidth of the pulsed laser radiation (2) in the multi-pass gas cell (8): - temporal pulse compression of the pulsed laser radiation (2) in a dispersion arrangement (6) which has at least two dispersive elements (Gl, G2), in particular optical gratings, which are designed to spatially separate the frequency components of the pulsed laser radiation (2) by a second predetermined amount and, after propagation over a frequency-dependently different optical path length, to combine the frequency components of the pulsed laser radiation (2) according to the second amount, so that a temporal pulse compression of the pulsed laser radiation (2) is achieved. will work. 4. The method according to claim 3, wherein for spatially separating the frequency components of the pulsed laser radiation (2) by the second predetermined amount, the frequency components of the pulsed laser radiation (2) are diffracted into different angles with a first (Gl) of the at least two dispersive elements (Gl, G2) and the frequency components of the pulsed laser radiation (2) diffracted into different angles are collimated with a second (G2) of the at least two dispersive elements (Gl, G2); and for spatially combining the frequency components of the pulsed laser radiation (2) according to the second extent, the frequency components of the pulsed laser radiation (2) are diffracted into different angles with the second (G2) of the at least two dispersive elements (Gl, G2) and the frequency components of the pulsed laser radiation diffracted into different angles with the first (Gl) of the at least two dispersive elements (Gl, G2) tion (2). 5. Method according to claim 4, wherein the spatial separation of the frequency components of the pulsed laser radiation (2) is carried out to the first predetermined extent in the direction perpendicular to the direction of propagation of the pulsed laser radiation (2) in that a first optical path length of the pulsed laser radiation (2) between the first (Gl) of the at least two dispersive elements (Gl, G2) and the second (G2) of the at least two dispersive elements (Gl, G2) during spatial separation of the frequency components of the pulsed laser radiation (2) differs by the second predetermined extent from a second optical path length of the pulsed laser radiation (2) between the second (G2) of the at least two dispersive elements (Gl, G2) and the first (Gl) of the at least two dispersive elements (Gl, G2) during spatial merging of the frequency components of the pulsed laser radiation (2) according to the second dimension. 6. Method according to one of claims 3 to 5, wherein the spatial separation of the frequency components of the pulsed laser radiation (2) in the first predetermined extent in the direction perpendicular to the direction of propagation of the pulsed laser radiation (2) during the temporal pulse compression of the pulsed laser beam device (2) with a separation element (7) in the dispersion order (6). 7. The method according to claim 6, wherein the pulsed laser radiation (2) in the dispersion arrangement (6) is reflected by a mirror (RM), wherein the pulsed laser radiation (2) in the dispersion arrangement (6) is guided along a first optical path (9) to the mirror and, after reflection at the mirror, is propagated along a second optical path (10), wherein the at least two dispersive elements (Gl, G2) are located in the first optical path (9) and in the second optical path (10), wherein the separation element (7) is only located in the first optical path (9) or only in the second optical path (10). 8. The method according to any one of claims 6 or 7, wherein the separating ration element (7) has four mirrors (M1l, M2, M3, M4). 9, Method according to one of the preceding claims, further comprising the following steps, which are carried out before the spatial separation of the frequency components of the pulsed laser radiation (2) to the first predetermined extent: - temporally broadening the pulsed laser radiation (2); - amplifying the temporally broadened pulsed laser radiation (2). 10. Device for manipulating pulsed laser radiation (2), comprising: - a device (3) for providing pulsed laser radiation (2); - a separation element (7) for spatially separating the frequencies of the pulsed laser radiation (2) to a first predetermined extent in a direction perpendicular to a propagation direction of the pulsed laser radiation (2); - a multiple-pass gas cell (8) for increasing the spectral bandwidth of the pulsed laser radiation (2) for temporal pulse compression of the pulsed laser radiation (2), wherein the multiple-pass gas cell (8) is arranged in the optical path of the pulsed laser radiation (2) after the separation element (7). net is. 11. Device according to claim 10, comprising a dispersion arrangement (6), preferably a grating pair pulse compressor, in particular a Treacy pair pulse compressor, for temporal pulse compression of the pulsed laser radiation (2) with at least two dispersive elements (Gl, G2), especially optical gratings. 12. Device according to claim 11, wherein the dispersion arrangement (6) has a mirror (RM) which is arranged so that the pulsed laser radiation (2) in the dispersion arrangement (6) is propagated along a first optical path (9) to the mirror (RM) and after reflection at the mirror (RM) is propagated along a second optical path (10), wherein the at least two dispersive elements (Gl, G2) are located in the first optical path (9) and in the second optical path (10), wherein the separation element is only in the first optical path (9) or only in the second optical path (10) is provided. 13. Device according to one of claims 10 to 12, wherein the separation device (7) comprises four mirrors (M1l, M2, M3, M4). points. 14. Device according to one of claims 10 to 13, comprising: - a broadening device (4) for temporally broadening the pulsed laser radiation (2); - an amplification device (5) for amplifying the temporally broadened pulsed laser radiation (2); wherein the separation element (7) and the multiple pass gas cell (8) are arranged in the optical path of the pulsed laser radiation (2) after the widening device (4) and the amplification device direction (5).