Optical device and method for spectral broadening of laser pulses, method for designing a nonlinear broadening element, and kit

Abstract

The present invention relates to an optical device (1) for spectrally broadening a laser pulse (5) to achieve nonlinear pulse compression, the optical device having a broadening path (3) arranged to guide the laser pulse (5) to pass repeatedly through at least one nonlinear broadening element (7), wherein the nonlinear broadening element (7) has scattering characteristics, and the scattering characteristics are selected such that the scattering characteristics compensate for self-focusing of the laser pulse (5) in the nonlinear broadening element (7).

Description

Field of the Invention

[0001] The present invention relates to an optical device for spectrally broadening laser pulses, a method for spectrally broadening laser pulses, a method for designing a nonlinear broadening element, and a kit having such a nonlinear broadening element. Background Art

[0002] In order to shorten laser pulses in time, nonlinear pulse compression methods are often applied. In this method, first, the laser pulses are spectrally broadened by self-phase modulation, and then these laser pulses are compressed in time. To spectrally broaden the laser pulses, the laser pulses are sent through a nonlinear medium, where Kerr nonlinearity occurs, that is, the refractive index changes by Δn = n2I, where I is the intensity and n2 is the nonlinear refractive index. The intensity of the laser pulse has a temporal envelope I(t), so the phase of the pulse is rapidly modulated in time according to the following formula: Φ(t) = k n ΔnL = k n n2I(t)L, where k n is the wave number and L is the propagation length in the medium. According to the relationship new frequencies are generated. Therefore, the spectrum of the laser pulse is continuously broadened when propagating in the nonlinear medium. If the dispersion is negligible, the pulse shape remains constant and the pulse exhibits chirp. Next, the pulse can be compressed in time by removing the chirp.

[0003] The problem here is that self-phase modulation (SPM) always occurs in combination with self-focusing (SF). Self-focusing causes the beam diameter of the laser pulse to narrow, the beam quality to deteriorate until complete collapse, especially filamentation. Summary of the Invention

[0004] The present invention is based on the following object: to provide an optical device for spectrally broadening laser pulses for nonlinear pulse compression, a method for spectrally broadening laser pulses, a method for designing a nonlinear broadening element, and a kit having such a nonlinear broadening element, in which the above-mentioned disadvantages do not occur.

[0005] This object is achieved by the provided technical teaching of the present invention, in particular by the teaching of the independent claims and the technical teaching of the embodiments disclosed in the dependent claims and the specification.

[0006] In particular, this object is achieved by providing an optical device for spectrally broadening a laser pulse for use in non-linear pulse compression, the optical device having a broadening path which is arranged to guide the laser pulse to pass repeatedly or multiple times through at least one non-linear broadening element, wherein the non-linear broadening element has a scattering property (Zerstreuungseigenschaft) which is selected such that the scattering property compensates for the self-focusing of the laser pulse in the non-linear broadening element. This makes it possible in particular to achieve a high spectral broadening and at the same time a compact construction without reducing the beam quality at least in relevant criteria due to self-focusing. The beam diameter of the laser pulse can advantageously be kept constant, in particular collimated. A strong spectral broadening of the laser pulse spectrum can in particular also be achieved by passing the laser pulse multiple times through at least one non-linear broadening element, which can in particular also be achieved by passing the laser pulse through a plurality of non-linear broadening elements, in particular successively through non-linear broadening elements of the same construction as one another, wherein each non-linear broadening element compensates for the self-focusing occurring therein due to its scattering property, or wherein the self-focusing is compensated for each time the laser pulse passes through the non-linear broadening element. Here, if a plurality of non-linear broadening elements are provided, the laser pulse does not have to pass through one of the non-linear broadening elements multiple times or through all of the non-linear broadening elements multiple times. Instead, if a plurality of non-linear broadening elements are provided and the laser pulse passes through these non-linear broadening elements, the laser pulse can also pass through each non-linear broadening element only once.

[0007] The non-linear broadening element is understood to mean an element, in particular an optical element or a structural element, which has an optically non-linear medium or consists of a non-linear medium, in particular such that when a laser pulse passes through the element or the structural component, Kerr non-linearity occurs in the optical element or the structural component, such that the laser pulse undergoes self-phase modulation and thus undergoes spectral broadening.

[0008] The scattering property is to be understood to mean the defocusing property of the non-linear broadening element. Thus, the non-linear broadening element in particular has a defocusing property which is coordinated (abgestimmt) with the self-focusing occurring in the non-linear broadening element such that the self-focusing is compensated for by the defocusing property of the non-linear broadening element. In this way, the beam remains at least almost collimated.

[0009] Compensating for self-focusing by the scattering property, in particular the defocusing property, in particular means that the self-focusing is cancelled out by the scattering property, in particular the defocusing property, by at least 80% to at most 120%, preferably at least 90% to at most 110%, preferably at least 95% to at most 105%, preferably at least 99% to at most 101%, preferably exactly cancelled out, i.e. 100%. Thus, the collapse of the laser pulse, in particular filamentation, is effectively prevented.

[0010] At least one nonlinear broadening element is preferably provided for additionally compensating for the self-focusing that the laser pulse undergoes in at least one medium, which is arranged in the environment of the nonlinear broadening element or in which the nonlinear broadening element is arranged. The medium can be a gaseous medium, a liquid medium or a solid medium, or even a plurality of media.

[0011] Advantageously, the optical device proposed here can keep the laser pulse at least almost constantly, preferably constantly, collimated. In addition, the optical device can be realized in a space-saving, especially small, cost-effective and compact manner. The optical device can be easily scaled up to higher pulse energies and medium outputs. The optical device is particularly suitable for laser pulses with a time range between 1 ps and several tens of fs. It is possible to enhance the contrast by means of nonlinear elliptical rotation. Especially in the case of a suitable antireflection coating on at least one nonlinear broadening element, the optical device can advantageously have almost no optical losses.

[0012] According to an expansion scheme of the present invention, the broadening path is provided for guiding the laser pulse: a) passing through at least one nonlinear broadening element multiple times, or b) passing through a plurality of nonlinear broadening elements once, and these nonlinear broadening elements are preferably arranged spaced apart from each other. It is also possible for the nonlinear broadening elements to be directly adjacent to each other. As already discussed, repeatedly guiding the laser pulse through at least one nonlinear broadening element can thus be achieved in particular by: sending the same laser pulse through at least one nonlinear broadening element multiple times, or guiding the laser pulse, especially once, through a plurality of nonlinear broadening elements, where the nonlinear broadening elements are preferably arranged spaced apart from each other in the propagation direction of the laser pulse. That is, it is not necessarily required that the laser pulse passes through the same nonlinear broadening element multiple times, but this configuration is not excluded either.

[0013] The optical device can in particular have six, seven, eight, nine, ten or more than ten nonlinear broadening elements.

[0014] If the optical device has a plurality of nonlinear broadening elements, then preferably each nonlinear broadening element among the plurality of nonlinear broadening elements has a scattering characteristic, and the scattering characteristics are respectively selected such that the scattering characteristics compensate for the self-focusing of the laser pulse in the corresponding nonlinear broadening element.

[0015] A suitable upper limit for the number of non-linear broadening elements in the broadening path is, for example, ten, where the exact number depends in particular on the thickness of the non-linear broadening element measured in the propagation direction of the laser pulse. Adding more broadening elements does not necessarily lead to further spectral broadening, since the dispersion occurring in the material of the non-linear broadening element causes an increase in the temporal broadening of the laser pulse, which in turn leads to a reduction in the instantaneous intensity, which ultimately terminates self-phase modulation. When the desired spectral broadening has been obtained by self-phase modulation, a suitable upper limit for the number of non-linear broadening elements is naturally also obtained.

[0016] According to an expansion scheme of the present invention, the non-linear broadening element has its scattering characteristics due to the end face of the non-linear broadening element of the concave shape. This represents a particularly simple configuration of the non-linear broadening element (including its scattering characteristics), which can be easily and cost-effectively produced. The end face of the non-linear broadening element is in particular the surface through which the laser pulse traveling through the broadening path passes as expected, i.e., in particular the beam incident surface or the beam exit surface of the non-linear broadening element. The scattering characteristics are preferably due to the concave shape of the beam incident surface and / or the beam exit surface, particularly preferably due to the concave shape of the beam incident surface of the non-linear broadening element. Very particularly preferably, only the beam incident surface has an at least regionally concave shape, while at the same time the beam exit surface preferably has a planar geometry. The concave shape of the end face can be produced or introduced during the manufacture of the non-linear broadening element. However, it is also possible to introduce the concave shape into the end face or to produce the concave shape on the end face at a later time, in particular by milling (preferably with a diamond milling cutter), grinding and / or polishing.

[0017] Alternatively or additionally, the non-linear broadening element can also have its scattering characteristics due to a holographic structure or a grating-type structure arranged in particular on the beam incident side and / or the beam exit side. In this case, the front face of the non-linear broadening element can be constructed flat. The holographic structure or the grating-type structure can be constructed in the volume of the non-linear broadening element - in particular regionally, i.e., locally.

[0018] Alternatively or additionally, at least one front side of the non-linear broadening element can also have the structure of a Fresnel lens or be constructed in the manner of a Fresnel lens to provide scattering characteristics.

[0019] Alternatively or additionally, the scattering characteristics can also be provided by stretching the non-linear broadening element in the form of a film.

[0020] According to an expansion scheme of the present invention, the end face of the non-linear broadening element and the spatial intensity profile of the laser pulse in the laser beam cross-section plane coordinated, in particular corresponding to the spatial profile of the laser pulse in the cross-sectional plane - possibly apart from a scale factor - or set to be proportional to the intensity profile. The shape of the end face is thus in particular coordinated with the defined intensity profile of the following laser pulse, and the nonlinear broadening element is used as expected with this laser pulse. This allows the local dispersion, in particular defocusing, to be matched to the local intensity, where regions in the laser profile that are expected to have strong self-focusing due to high intensity, in particular the edge regions, are scattered, in particular defocused, more strongly than regions in the intensity profile where little or no self-focusing is expected due to low intensity, in particular the edge regions. In this way, self-focusing of the laser pulse can be reduced or even prevented in a particularly advantageous manner, and in particular in regions where little or no self-focusing occurs in the profile, the laser beam is not additionally spatially broadened. Thus, a particularly high beam quality is preferably generated or maintained.

[0021] In a particularly preferred manner, the end face of the nonlinear broadening element is shaped in a Gaussian shape. The end face in particular has a Gaussian profile (Gauβprofil), particularly preferably the Gaussian profile of the laser pulse, the nonlinear broadening element is arranged to spatially broaden this laser pulse as expected, and the profile of the end face is correspondingly coordinated with the intensity profile of this laser pulse. Here, in particular, the branches of the intensity profile are less defocused than the central region, such that the scattering characteristics of the nonlinear broadening element are coordinated with the local intensity level and thus with the local self-focusing characteristics of the laser pulse in the nonlinear broadening element.

[0022] According to an expansion scheme of the present invention, the at least one nonlinear broadening element is arranged in a vacuum. The optical device, in particular the broadening path, can thus be evacuated at least regionally. This advantageously allows suppression of the disturbing effects of the gaseous medium. The beam guide is usually already arranged regionally in a vacuum, and thus, in this case, arranging at least one nonlinear broadening element in a vacuum as well is a particularly simple configuration.

[0023] Alternatively, it is preferably arranged that the at least one nonlinear broadening element is arranged in a gaseous medium or a liquid medium. In this way, compared to the case of being at least regionally evacuated, the optical device, in particular the broadening path, can be configured to be technically simpler and more cost-effective. The gaseous medium can in particular be air, an inert gas such as nitrogen or carbon dioxide, or a noble gas, or a mixture of at least two of the above gases. A solid medium such as a vitreous body can also be arranged between two nonlinear broadening elements.

[0024] According to an extended embodiment of the invention, the optical device has a plurality of broadening paths, and between each two broadening paths, a pulse compression device for temporally compressing the laser pulse is arranged. This corresponds to a cascade of the optical device, in particular a cascade of the broadening paths, wherein at least one nonlinear broadening element of a single broadening path respectively generates a broadened spectrum, and then the spectrum is compressed into a laser pulse with a shorter time by the pulse compression device, and then the laser pulse is spectrally broadened by a subsequent broadening path, and then compressed again, and this can be carried out continuously for many times, basically infinitely. In this way, particularly short laser pulses can be obtained. Thereby, in particular, the aforementioned inherent limitation can be circumvented, which is caused by the fact that after passing through the nonlinear broadening element multiple times, the pulse duration of the laser pulse in time becomes too long due to dispersion, so that no further self-phase modulation occurs. The interposed pulse compression causes a shortening of the time of the laser pulse, and thus self-phase modulation still occurs in the subsequently connected broadening path.

[0025] The pulse compression device can in particular have at least one chirped mirror, at least one grating or at least one other suitable dispersive element, in particular a combination of at least two of said elements.

[0026] According to an extended embodiment of the invention, at least one nonlinear broadening element is configured as a plate-shaped element, in particular as a small plate, or as a thin film. This is a particularly compact, simple and cost-effective configuration of the nonlinear broadening element. In a preferred configuration, the nonlinear broadening element is preferably configured as a small glass plate, a small crystal plate or a small composite plate made of different materials, preferably sintered. The nonlinear broadening element can preferably include fused silica or consist of fused silica.

[0027] According to an extended embodiment of the invention, the at least one nonlinear broadening element has a thickness of at least 2 mm, preferably at least 10 mm to at most 50 mm, preferably at least 15 mm to at most 40 mm in the beam propagation direction of the laser pulse, i.e., in the propagation direction. In this way, the optical device can be configured in a highly compact manner. The concave shape of the end face of the at least one non-linear broadening element preferably has a range of at least 1 μm to at most 100 μm, preferably at least 10 μm to at most 40 μm, preferably at least 15 μm to at most 30 μm, preferably 20 μm, in the beam propagation direction, i.e., in the propagation direction. Here, the range of the concave shape is preferably measured from the outermost point of the end face to the minimum value of the concave shape, for example, especially from the outermost branch of the Gaussian profile to the maximum value of the Gaussian profile, which point simultaneously corresponds to the minimum value of the Gaussian-shaped depression that is the concave shape. The range of the concave shape of the end face is in any case preferably much smaller than the range corresponding to the thickness of the non-linear broadening element in the beam propagation direction.

[0028] The scattering properties of the non-linear broadening element preferably have a particularly large negative focal length, which is especially several meters, especially dozens of meters, such as 20 m or 22 m. Thus, the scattering properties of the non-linear broadening element, especially the defocusing properties, are not very pronounced and are chosen to just compensate for the self-focusing of the laser pulse in the non-linear broadening element. In addition, the non-linear broadening element preferably does not have any defocusing or focusing properties, especially no lens properties.

[0029] The object is also solved by a method for spectrally broadening a laser pulse for non-linear pulse compression, in which the laser pulse is guided through at least one non-linear broadening element repeatedly or multiple times. The non-linear broadening element has scattering properties here, which are chosen such that the scattering properties compensate for the self-focusing of the laser pulse in the non-linear broadening element. This in turn means that, within the scope of this method, the self-focusing occurring in the non-linear broadening element is compensated by the scattering properties of the non-linear broadening element. Within the scope of this method, in particular, the advantages already described in connection with the optical device are obtained. Within the scope of this method, an optical device according to the invention or an optical device according to one of the previously described embodiments is preferably used.

[0030] Before guiding the laser pulse through at least one non-linear broadening element, the laser pulse can preferably be temporally broadened by chirping, i.e., the laser pulse can actually be pre-chirped.

[0031] Guiding a laser pulse repeatedly through at least one nonlinear broadening element especially includes the following cases: guiding the laser pulse through at least one nonlinear broadening element multiple times; or guiding the laser pulse through multiple nonlinear broadening elements once, and the multiple nonlinear broadening elements are preferably spaced apart from each other or adjacent to each other. Here, it is not absolutely necessary for the laser beam to pass through the same nonlinear broadening element multiple times. However, such a configuration is possible. According to a preferred configuration, the laser pulse can pass through at least one nonlinear broadening element in a double-pass (Doppeldurchgang) manner if the nonlinear broadening element is reflectively coated on its preferably flat rear side facing away from the beam.

[0032] This object is also solved by providing a method for designing a nonlinear broadening element, which is used in an optical device according to the present invention or an optical device according to one of the previously described embodiments, or in a method for spectrally broadening a laser pulse according to the present invention or an implementation of a method for spectrally broadening a laser pulse. Here, for a determined laser pulse, the thickness for the nonlinear broadening element is set (festgelegt). The thickness of the nonlinear broadening element is its extent or thickness (Dicke) in the propagation direction of the laser pulse, i.e., in the propagation direction. For a determined laser pulse, self-focusing in the nonlinear broadening element with the set thickness is determined (especially calculated or simulated) or determined experimentally. The scattering characteristics of the nonlinear broadening element are determined such that the scattering characteristics compensate for the self-focusing of the laser pulse in the nonlinear broadening element. The thus determined scattering characteristics are configured on the nonlinear broadening element. In this way, in particular, a nonlinear broadening element is obtained that is suitable and arranged for use in the corresponding optical device or the corresponding method for spectral broadening.

[0033] When designing the at least one nonlinear broadening element, it is preferably additionally considered that the laser pulse undergoes self-focusing in at least one medium, which is arranged in the surrounding environment of the nonlinear broadening element as expected or in which the at least one nonlinear broadening element is arranged as expected. The medium can be a gaseous medium, a liquid medium, or a solid medium, or even multiple media. Preferably, this self-focusing is compensated by a correspondingly designed nonlinear broadening element.

[0034] The design of the nonlinear broadening element is especially understood as setting the configuration of the nonlinear broadening element, especially the spatial geometric configuration.

[0035] Here, a defined laser pulse is understood as a laser pulse that is set in particular with respect to its parameters (in particular its wavelength or spectral composition, its spatial intensity profile in a cross-sectional plane perpendicular to the propagation direction, its temporal intensity profile (i.e., the temporal envelope of the intensity profile I(t)), and / or its temporal pulse width, pulse power, and / or pulse energy).

[0036] The scattering properties of the nonlinear broadening element are preferably determined by calculation, particularly preferably by simulation. However, experimental determination is also possible.

[0037] Preferably, the scattering properties are configured on the nonlinear broadening element by machining at least one end face of the nonlinear broadening element, in particular by milling (preferably with a diamond milling cutter), grinding, and / or polishing. However, alternatively or additionally, the scattering properties can also be introduced or generated during the manufacture of the nonlinear broadening element, for example by a corresponding shaping process (Formgebung) during molding or by pressing.

[0038] According to an expansion scheme of the present invention, the scattering properties are configured as a concave shape on the end face of the nonlinear broadening element. Here, the shape of the end face is particularly preferably coordinated with the spatial intensity profile of the laser pulse in a cross-sectional plane perpendicular to the propagation direction; the shape is particularly selected according to the spatial intensity profile. Particularly preferably, the scattering properties are configured as a Gaussian shape on the end face of the nonlinear broadening element, especially in the case where the laser pulse is a fundamental mode pulse (TEM00 or diffraction-limited pulse).

[0039] In a preferred embodiment of the method, the range of the scattering properties, in particular the concave shape, of the end face of the broadening element in the beam propagation direction is limited to at least 5 μm. This advantageously enables the simple and cost-effective production of the broadening element. Furthermore, the thickness of the broadening element in the beam propagation direction is preferably limited to at most 50 mm. The thickness of the broadening element and the range of the scattering properties are preferably coordinated with each other and with the defined laser beam used together with the broadening element such that the minimum range of the scattering properties is not undershot. If the coordinated thickness of the broadening element exceeds the maximum thickness (e.g., due to a lower energy of the defined laser beam and / or a larger beam diameter), then for the defined laser beam used together with the broadening element, the thickness of at least one additional AR coating (i.e., anti-reflection coating) element is preferably set, or the number of additional AR coating elements of a defined thickness is set accordingly, where the thickness of the at least one additional AR coating element or the sum of the thicknesses of the number of additional AR coating elements is taken as the difference between the sought thickness of the broadening element and the maximum thickness of the broadening element.

[0040] According to an extended embodiment of the invention, the scattering properties are coordinated with the intensity profile of a defined laser pulse. In particular, corresponding to the intensity profile of a defined laser pulse, the scattering properties are selected, in particular, proportionally to the intensity profile of the laser pulse or identically to the intensity profile.

[0041] Finally, this object is also solved by providing a kit, wherein the kit has a nonlinear broadening element having scattering properties that are coordinated with a defined laser pulse such that the scattering properties compensate for self-focusing of the defined laser pulse in the nonlinear broadening element. The kit also includes instructions for use having at least one instruction for using the nonlinear broadening element with a defined laser pulse. The coordination of the scattering properties with the properties of the defined laser pulse is particularly reflected in the instructions for use. Thus, the user of the kit, in particular the nonlinear broadening element, is informed by the instructions for use that the nonlinear broadening element should be used together with a defined laser pulse, in particular a defined laser pulse defined by the above-mentioned properties.

[0042] In one embodiment of the kit, the scattering properties of the broadening element, in particular the concave shape, have a minimum extent of 5 μm in the beam propagation direction. The broadening element preferably has a maximum thickness of 50 mm. The kit also includes at least one AR coating element having a specific thickness and no scattering properties. If, based on the maximum thickness of the broadening element and the resulting self-focusing, the scattering properties of the broadening element with the minimum extent are too pronounced for a defined laser beam, the self-focusing of the laser pulse can be enhanced by means of the at least one AR coating element having no scattering properties.

[0043] According to an extended embodiment of the invention, the nonlinear broadening element of the kit has scattering properties that are coordinated with the intensity profile of the defined laser pulse in a cross-sectional plane perpendicular to the propagation direction of the laser pulse. The scattering properties are in particular proportional to the intensity profile or identical to the intensity profile.

[0044] The kit in particular has a nonlinear broadening element as previously described in connection with the optical device.

[0045] In connection with the kit, in particular, the advantages already mentioned in connection with the optical device, the method for spectral broadening and the method for designing a nonlinear broadening element are achieved. Description of the Drawings

[0046] The invention is explained in more detail below on the basis of the drawings, in which:

[0047] Figure 1 A schematic diagram showing an embodiment of an optical device for spectral broadening of a laser pulse and its influence on the spectrum of the laser pulse;

[0048] Figure 2 Schematic diagram showing the operating principle of the nonlinear broadening element of an optical device;

[0049] Figure 3 Schematic diagram showing the effect of the optical device, and

[0050] Figure 4 Schematic diagram showing an embodiment of an equipment set having a nonlinear broadening element. Detailed implementation mode

[0051] Figure 1 Schematic diagram showing an embodiment of an optical device 1 for spectrally broadening a laser pulse to achieve nonlinear pulse compression. Here, a) shows the optical device 1 having a broadening path 3, which is arranged to guide the shown laser pulse 5 repeatedly or multiple times through at least one nonlinear broadening element 7. In the embodiment shown here, the broadening path 3 has ten nonlinear broadening elements 7, where, for clarity, only the first nonlinear broadening element 7 in the propagation direction of the laser pulse 5 (i.e., when looking from left to right) is denoted by the corresponding reference numeral. Here, the nonlinear broadening elements 7 are schematically shown respectively by the vertical solid line on the left side and the dashed line on the right side, and these two lines represent the boundaries of the corresponding nonlinear broadening element 7 in the propagation direction. It is clearly shown here that the ten nonlinear broadening elements 7 are spaced apart from each other.

[0052] In Figure 1 a), the radius R of the laser pulse 5 is also plotted relative to the propagation distance s. In addition, Figure 1 the right part of the figure in a) shows the intensity profile I of the laser pulse 5 in a plane perpendicular to the propagation direction (i.e., according to the radius R). This shows that the laser pulse 5 has an intensity profile with a Gaussian shape in this case.

[0053] In Figure 1 b) shows that the spectrum of the laser pulse 5 is broadened when passing through the broadening path 3. Here, the intensity I of the laser pulse 5 is plotted relative to the wavelength λ. The first virtual curve K1 shows the spectrum of the laser pulse 5 before passing through the broadening path 3 (i.e., before entering the first nonlinear broadening element 7), where this spectrum is relatively narrowly concentrated around the central wavelength λ0. The spectrum of the laser pulse 5 after passing through the broadening path 3 is shown by the second solid curve K2, where it is clear that the spectrum of the laser pulse 5 is significantly broadened due to the laser pulse passing through the nonlinear broadening element 7.

[0054] This is based on self-phase modulation caused by the Kerr nonlinearity that occurs when the laser pulse 5 passes through the nonlinear medium of the broadening element 7.

[0055] Figure 2Schematic diagram showing the operating principle of the optical device 1.

[0056] Identical or functionally identical elements are provided with the same reference numerals in all the figures and are thus respectively referred to the above description.

[0057] In a), a conventional non - linear broadening element 7' is schematically shown. When the laser pulse 5 passes through the conventional broadening element 7', the laser pulse not only undergoes self - phase modulation but also uncorrected self - focusing, whereby the radial intensity profile becomes narrower. Especially when the laser pulse passes through a plurality of non - linear broadening elements 7' or through a correspondingly thicker non - linear broadening element 7' (i.e., a non - linear broadening element extending in the propagation direction), this can lead to instability of the laser pulse 5 and ultimately complete collapse, especially filamentation.

[0058] To avoid this, in Figure 2 b), the non - linear broadening element 7 according to the invention shown in one embodiment has scattering properties which are selected such that the scattering properties compensate and thus correct the self - focusing of the laser pulse 5 in the non - linear broadening element 7. Preferably, each non - linear broadening element 7 of the broadening path 3 in particular has corresponding scattering properties.

[0059] In Figure 2 the embodiment shown in b), the scattering properties are formed by the concave shape of the end face 9 of the non - linear broadening element 7 (specifically the beam incident face 10 in this case). Additionally or alternatively, the beam exit face 12 can also have a corresponding concave shape.

[0060] The scattering properties, in particular the concave shape of the end face 9, are preferably coordinated with the intensity profile of the laser pulse 5. The end face 9 in particular has a Gaussian shape. Thus, the center of the laser pulse 5 with high intensity is defocused more strongly compared to the radial outer branches of the intensity profile, where, through the non - linear broadening element 7, the intensity profile of the laser pulse 5 ultimately remains at least substantially unchanged because the self - focusing effect of the non - linear medium on the one hand and the defocusing properties of the non - linear broadening element 7, especially due to the concave shape of the end face 9, at least substantially cancel each other out, or rather the concave shape of the end face 9 pre - compensates for the self - focusing.

[0061] Viewed in the beam propagation direction of the laser pulse, the non - linear broadening element 7 preferably has a thickness of at least 2 mm, preferably at least 10 mm to at most 50 mm, preferably at least 15 mm to at most 40 mm. The concave shape of the end face 9 preferably has a range of at least 1 μm to at most 100 μm, preferably at least 10 μm to at most 40 μm, preferably at least 15 μm to at most 30 μm, preferably 20 μm in the beam propagation direction.

[0062] Figure 3Schematic illustration of the effect of the non - linear broadening element 7 according to the invention compared to a conventional broadening element 7'. Here, a) shows the variation of the diameter D of the laser pulse 5 at a fraction 1 / e of the peak intensity plotted against the propagation distance s for a plurality of conventional non - linear broadening elements 7' arranged one behind the other in a configuration similar to Figure 1 a). Here, it is shown that due to self - focusing, the diameter D decreases with increasing propagation. 2 In b), for the arrangement of the non - linear broadening element 7 according to the invention, the same plot is shown in the

[0063] configuration of a). Here, it is shown that the diameter D remains at least substantially constant along the propagation distance. Figure 1 Returning to

[0064] a), it should also be noted that the broadening path 3 is preferably arranged to guide the laser pulse 5 through at least one non - linear broadening element 7 multiple times, or alternatively - as shown in Figure 1 a) - through a plurality of non - linear broadening elements 7 in a single pass, where these non - linear broadening elements are arranged spaced apart from each other in a preferred configuration. Figure 1

[0065] The non - linear broadening element 7 can be arranged in a vacuum, or in a gaseous or liquid medium, in particular air, nitrogen, carbon dioxide or at least one noble gas. A solid medium can also be arranged between the non - linear broadening elements 7.

[0066] Figure 1 The shown device can also be cascaded, where there can be a plurality of broadening paths 3, and between every two broadening paths, a pulse compression device 11 (only indicated schematically here) for temporally compressing the laser pulse 5 can be arranged.

[0067]

[0068] The non - linear broadening element 7 is preferably configured as a plate - shaped element, in particular a small glass plate or a small crystal plate, or as a thin film.

[0069] The non - linear broadening element 7 is preferably designed such that for a defined laser pulse, the thickness (measured in the propagation direction) of the non - linear broadening element 7 is set, where for the defined laser pulse 5, the self - focusing in the non - linear broadening element 7 with the set thickness is determined, in particular calculated, and the scattering properties of the non - linear broadening element 7 are determined such that the scattering properties compensate for the self - focusing of the defined laser pulse 5 in the non - linear broadening element 7. Here, the scattering properties are determined in particular by simulation or experimentally. Finally, the scattering properties are fabricated on the non - linear broadening element 7. Thus, the non - linear broadening element 7 is finally obtained. Figure 4

[0069] Figure 4Schematic diagram showing an embodiment of the equipment set 13. The equipment set includes a non-linear broadening element 7 having scattering characteristics that are coordinated with a defined laser pulse 5 in such a way that the scattering characteristics compensate for self-focusing of the defined laser pulse 5 in the non-linear broadening element 7. In addition, the equipment set 13 includes operating instructions 15, in respect of which the operating instructions include at least one instruction for using the non-linear broadening element 7 with the defined laser pulse 5.

Claims

1. An optical device (1) for spectrally broadening a laser pulse (5) for non-linear pulse compression, the optical device having a broadening path (3) arranged to guide the laser pulse (5) repeatedly through at least one non-linear broadening element (7), wherein, The nonlinear broadening element (7) has scattering properties, and the scattering properties are selected such that the scattering properties compensate for the self-focusing of the laser pulse (5) in the nonlinear broadening element (7), wherein the end face (9) of the nonlinear broadening element (7) has a concave shape, and wherein the scattering properties are provided by the concave shape of the end face (9), characterized in that the end face (9) of the nonlinear broadening element (7) is shaped as a Gaussian shape.

2. The optical device (1) according to claim 1, characterized in that, The broadening path (3) is arranged to guide the laser pulse (5) a) through the at least one nonlinear broadening element (7) multiple times, or b) through a plurality of nonlinear broadening elements (7) once.

3. The optical device (1) according to claim 1 or 2, characterized in that, The at least one nonlinear broadening element (7) is arranged in a vacuum, or in a gaseous medium or a liquid medium.

4. The optical device (1) according to claim 1 or 2, characterized in that, The optical device (1) has a plurality of broadening paths (3), wherein a pulse compression device (11) for temporally compressing the laser pulse (5) is arranged between every two broadening paths (3).

5. The optical device (1) according to claim 1 or 2, characterized in that, The nonlinear broadening element (7) is configured as a plate-shaped element or as a thin film.

6. The optical device (1) according to claim 1 or 2, characterized in that, The at least one nonlinear broadening element (7) has a thickness of at least 2 mm in the beam propagation direction of the laser pulse (5).

7. The optical device (1) according to claim 5, characterized in that, The plate-shaped element is a small plate.

8. The optical device (1) according to claim 7, characterized in that, The small plate is a small glass plate or a small crystal plate.

9. The optical device (1) according to claim 6, characterized in that, The thickness is at least 10 mm to at most 50 mm.

10. The optical device (1) according to claim 9, characterized in that, The thickness is at least 15 mm to at most 40 mm.

11. The optical device (1) according to claim 6, characterized in that, Wherein, The concave shape of the end face (9) has a range of at least 1 μm to at most 100 μm in the beam propagation direction.

12. The optical device (1) according to claim 10, characterized in that, The range is at least 10 μm to at most 40 μm.

13. The optical device (1) according to claim 11, characterized in that, The range is at least 15 μm to at most 30 μm.

14. The optical device (1) according to claim 12, characterized in that, The range is 20 μm.

15. A method for spectrally broadening a laser pulse (5), wherein, The laser pulse (5) is guided to pass through the at least one nonlinear broadening element (7) repeatedly, wherein the nonlinear broadening element (7) has scattering properties, and the scattering properties are selected such that the scattering properties compensate for the self-focusing of the laser pulse (5) in the nonlinear broadening element (7), wherein the end face (9) of the nonlinear broadening element (7) has a concave shape, and wherein the scattering properties are provided by the concave shape of the end face (9), characterized in that the end face (9) of the nonlinear broadening element (7) is shaped as a Gaussian shape.

16. A method for designing a nonlinear broadening element (7), the nonlinear broadening element (7) being used in the optical device (1) according to any one of claims 1 to 14 or in the method according to claim 15, wherein, - setting the thickness of the nonlinear broadening element (7) for a determined laser pulse (5), wherein, - determining the self-focusing in the nonlinear broadening element (7) having the set thickness for the determined laser pulse (5), wherein, - determining the scattering properties of the nonlinear broadening element (7) such that the scattering properties compensate for the self-focusing of the determined laser pulse (5) in the nonlinear broadening element (7), and wherein, -Construct such determined scattering characteristics on the non-linear broadening element (7) wherein the end face (9) of the non-linear broadening element (7) has a concave shape, and wherein the scattering characteristics are provided by the concave shape of the end face (9), characterized in that the end face (9) of the non-linear broadening element (7) is shaped as a Gaussian shape.

17. The method according to claim 16, wherein The scattering characteristics are constructed as a concave shape on the end face (9) of the non-linear broadening element (7).

18. The method according to claim 16 or 17, characterized in that, The scattering characteristics are coordinated with the intensity profile of the determined laser pulse (5).

19. A set of equipment (13), the set of equipment having a non-linear broadening element (7), the non-linear broadening element having scattering characteristics which are coordinated with a determined laser pulse (5) such that the scattering characteristics compensate for self-focusing of the determined laser pulse (5) in the non-linear broadening element (7), wherein, The kit (13) further includes instructions for use (15), the instructions for use having at least one instruction for using the non-linear broadening element (7) with the determined laser pulse (5), wherein the end face (9) of the non-linear broadening element (7) has a concave shape, and wherein the scattering characteristics are provided by the concave shape of the end face (9), characterized in that the end face (9) of the non-linear broadening element (7) is shaped as a Gaussian shape.

20. The complete set of equipment (13) according to claim 19, characterized in that, The scattering characteristics of the non-linear broadening element (7) are coordinated with the intensity profile of the determined laser pulse (5).

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