Device and laser arrangement for spectral broadening of a pulsed laser beam

Abstract

The invention relates to a device (10) for spectral broadening of a pulsed laser beam (12) by means of self-phase modulation, having the features of claim 1, and to a laser arrangement (32) for spectral broadening of a pulsed laser beam (12) by means of self-phase modulation, having the features of the additional independent claim.

Description

[0001]

[0002] Title: Device, laser arrangement and method for spectral broadening of a pulsed laser beam

[0003] Description

[0004] The invention relates to a device for spectral broadening of a pulsed laser beam by means of self-phase modulation with features of claim 1 and a laser arrangement for spectral broadening of a pulsed laser beam by means of self-phase modulation with features of claim 12.

[0005] Self-phase modulation (SPM) of a laser beam is a nonlinear optical effect based on the intensity dependence of the refractive index in materials. It occurs when an intense laser beam is passed through a nonlinear medium, undergoing a frequency-dependent phase shift that leads to the generation of new frequency components within the laser beam. This effect is of central importance for applications in the generation of ultrashort laser pulses via spectral broadening.

[0006] DE 10 2020 204 808 A1 discloses a device for spectral broadening of laser pulses by means of several mirror elements between which a laser beam is reflected back and forth. The laser beam passes through a disk-shaped nonlinear optical solid medium to generate a nonlinear phase by self-phase modulation. The mirror elements are arranged in a gas-filled chamber.

[0007] The object of the present invention is to provide a device, a laser system and a method for spectral broadening of a pulsed laser beam, in which the susceptibility to interference, the complexity, the costs and the required passes or passages of the laser beam can be reduced.

[0008] The above problem is solved by a device for spectral broadening of a pulsed laser beam by means of self-phase modulation with the features of claim 1. The spectral broadening can be performed in the pico- or femtosecond regime.

[0009] The device comprises a chamber filled with a gas or gas mixture. The chamber has a first transmission region and a second transmission region for the passage of the laser beam into and / or out of the chamber.

[0010] The device comprises at least one first mirror and at least one second mirror. The first and second mirrors are arranged outside the chamber and configured to reflect the laser beam multiple times, in particular more than four times, preferably more than ten times, between the first and second mirrors and through the chamber. The gas causes a spectral broadening of the laser beam.

[0011] Compared to a conventional gas-based multipass cell, the arrangement of mirrors within the vacuum chamber is unnecessary. This eliminates the need for complex mechanics required to prevent mirror misalignment during evacuation and gas filling of the chamber. The chamber size (especially length and diameter) can be reduced because the first and second mirrors are located outside the chamber. This significantly reduces the required gas volume. Adjusting and, in particular, verifying the laser beam size (or diameter) on the mirrors is simplified, as the first and second mirrors are directly accessible.

[0012] According to a further development of the device, it can be configured as a multipass cell. The device can be configured as a Herriott cell or a Bow-Tie cavity. It is also conceivable that the device could have a concave-convex structure or be configured as another folded cell. In particular, all optics can be arranged outside the chamber.

[0013] This allows the device to be implemented using simple means.

[0014] According to a further development of the device, the first transmission area and / or the second transmission area can comprise or be formed from a nonlinear optical solid medium.

[0015] This allows for the exploitation of gas-based and solid-state medium-based nonlinearities using simple means. The susceptibility to interference, the complexity, the costs, and the number of laser beam passes required for spectral broadening can be reduced. Due to the reduction in passes, the mirrors can be made smaller and more cost-effective.

[0016] Compared to a conventional solid-state-based multipass cell, significantly fewer passes or cycles are required due to the higher usable nonlinearity (B-integral) resulting from the additional use of the gas or gas mixture as a nonlinear medium. This allows the first and / or second mirror to be smaller, reducing material costs, losses, and the size of the device. Due to the additional nonlinearity provided by the gas or gas mixture, higher compression factors can be achieved (conventional solid-state-based multipass cells often require two propagation stages). According to a further development of the device, the gas in the chamber can be a noble gas, in particular argon, helium, krypton, or xenon. Alternatively, the gas mixture in the chamber can contain a noble gas, in particular argon, helium, krypton, or xenon.

[0017] This allows the device to be further optimized using simple means.

[0018] According to a further development of the device, the first mirror and the second mirror can be arranged such that the laser beam reflected between them forms a focus. It is also conceivable that the first mirror and the second mirror can be arranged such that the laser beam reflected between them forms a caustic.

[0019] This allows for the implementation of an optimal beam path using simple means.

[0020] According to a further development of the device, the first transmission area can include a window. The first transmission area can be configured as a window. The second transmission area can include a window. The second transmission area can be configured as a window.

[0021] This allows the respective transmission range to be implemented using simple means.

[0022] According to a further development of the device, the window can be made of fused silica or sapphire glass. It is also conceivable that the window could be made of another material. The window can comprise or be formed from a nonlinear optical solid medium. The window can have a thickness that withstands the pressure difference between the chamber and its surroundings. The window can exhibit nonlinearity in the range of π / 50 to π / 2, preferably π / 30 to π / 5.

[0023] This allows the window to be implemented using simple means.

[0024] According to a further development of the device, the window can have an anti-reflective coating. The anti-reflective coating can be applied to both sides or to one side of the window.

[0025] This allows reflections to be avoided or at least reduced, thus further optimizing the device.

[0026] According to a further development of the device, the first mirror and / or the second mirror can each be arranged at a distance from the chamber. Air can be arranged between the first mirror and the chamber. Alternatively or additionally, air can be arranged between the second mirror and the chamber.

[0027] This allows the first mirror and / or the second mirror to be implemented in the device using simple means.

[0028] According to a further development of the device, the chamber can be designed to be evacuated. This allows the nonlinear effect in the gas or gas mixture to be optimized.

[0029] According to a further development of the device, the chamber can be configured such that a gas pressure within the chamber can be adjusted. It is conceivable that the chamber can be pressurized with negative pressure. Likewise, it is conceivable that the chamber can be pressurized with positive pressure.

[0030] This allows the nonlinear effect in the gas or gas mixture to be further optimized.

[0031] According to a further development of the device, the chamber can have a base body. The base body can be designed as a tube. The base body can have a round, in particular circular, cross-section. The base body can be made of metal or glass. The base body can be designed as an (open) tube which is gas-tightly sealed at both (open) ends by means of a window. The base body can be filled with a desired gas or gas mixture before the two windows are attached or welded on.

[0032] This eliminates the need for a vacuum pump and other elements such as a gas connection, pressure gauge, pressure relief valve, gas distribution system, safety loops, etc.

[0033] This allows the device to be implemented with simple means. A conventional vacuum chamber is never perfectly sealed and usually requires the gas or gas mixture to be replaced or refilled after a certain operating period. Therefore, a conventional vacuum chamber requires gas cylinders, a safety concept, and infrastructure such as gas cabinets.

[0034] In contrast, the base unit with the windows can be completely welded shut, thus requiring neither a system shutdown nor a gas infrastructure. Precise adjustment is not necessary for positioning the base unit with the gas-tight welded windows, as all critical adjustment or service work can be carried out on components or optics located outside the chamber and therefore in air (or normal atmosphere), making them easily accessible.

[0035] The device is significantly simpler and easier to clean than a complex vacuum chamber with optics, optic holders, etc. This leads to increased durability of the device and the optics used.

[0036] The choice of window thickness, material, position, and gas type or gas mixture, as well as gas pressure, allows significantly more degrees of freedom in designing the self-phase modulation than a conventional gas-filled multipass cell.

[0037] Optical reflections can be captured and cooled much more easily in air than in a conventional vacuum chamber. Diagnostics, adjustment, and servicing are significantly simpler with this device, as all elements and optics (especially the first and second mirrors) are easily visible and not located within the chamber (vacuum chamber) where cameras would be needed to check the beam position / adjustment.

[0038] For each pass of the laser beam from the first mirror to the second mirror (or vice versa), the laser beam propagates twice through a window. For each window, or rather for each nonlinear optical solid medium, a B-integral (a measure of nonlinearity) in the range of π / 50 to π / 2, preferably π / 30 to π / 5, can be achieved. Furthermore, for each pass of the laser beam, a B-integral can be generated in the gas (or gas mixture), resulting in a total B-integral in the range of π / 20 to 4π, preferably π / 10 to 2π, per pass. By adjusting the gas pressure and the number of revolutions in the chamber, the spectral broadening can be tailored to achieve different pulse durations.

[0039] The above problem is further solved by a laser arrangement for spectral broadening of a pulsed laser beam by means of self-phase modulation with the features of claim 12. The spectral broadening can be carried out in the pico- or femtosecond regime.

[0040] The laser arrangement comprises a laser source. The laser source is configured to generate the laser beam. The laser arrangement comprises a device as described above. The laser arrangement includes coupling optics, in particular a mode-matching telescope, for coupling the laser beam into the device. The laser arrangement includes output optics, in particular a mirror, for coupling the laser beam out of the device.

[0041] Regarding the advantages achievable with the laser arrangement, reference is made to the relevant explanations concerning the device. The measures described in connection with the device and / or those explained below can be used for further development of the laser arrangement.

[0042] According to a further development of the laser arrangement, the laser arrangement can include a compressor, in particular a chirped mirror compressor or a grating compressor, for compressing the laser beam.

[0043] This allows the laser beam or its pulses to be compressed using simple means.

[0044] Further features, details and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. The drawings show:

[0045] Fig. 1 shows a schematic representation of a device for spectral broadening of a pulsed laser beam by means of self-phase modulation and

[0046] Fig. 2 shows a schematic representation of a laser arrangement with the device according to Figure 1.

[0047] In the following description and in the figures, corresponding components and elements bear the same reference symbols. For the sake of clarity, not all reference symbols are shown in every figure.

[0048] Figure 1 shows a schematic representation of a device 10 for spectral broadening of a pulsed laser beam 12 by means of self-phase modulation.

[0049] The device 10 comprises a chamber 16 filled with a gas 14 or gas mixture. The chamber 16 comprises a first transmission area 18 and a second transmission area 20 for the passage of the laser beam 12 into and / or out of the chamber 16.

[0050] The first transmission region 18 can comprise or be formed from a nonlinear optical solid medium 22. Alternatively or additionally, the second transmission region 20 can comprise or be formed from a nonlinear optical solid medium 22. The nonlinear optical solid medium 22 can cause a broadening of the laser beam 12.

[0051] The device 10 comprises at least one first mirror 24 and at least one second mirror 26. The first mirror 24 and the second mirror 26 are arranged outside the chamber 16. The chamber 16 can be arranged between the two mirrors 24 and 26. The first mirror 24 and the second mirror 26 are configured to reflect the laser beam 12 multiple times between the first mirror 24 and the second mirror 26 and through the chamber 16. The gas 14 causes spectral broadening of the laser beam 12. The device 10 can be configured as a multipass cell. Alternatively or additionally, the device 10 can be configured as a Herriott cell or a bow-tie cavity. It is also conceivable that the device 10 can be configured as another folded cell.

[0052] The gas 14 in chamber 16 can be a noble gas, in particular argon, helium, krypton, or xenon. In the case of a gas mixture in chamber 16, the gas mixture can comprise a noble gas, in particular argon, helium, krypton, or xenon.

[0053] The first mirror 24 and the second mirror 26 can be configured such that the laser beam 12 reflected between them forms a focus. It is also conceivable that the first mirror 24 and the second mirror 26 can be configured such that the laser beam 12 reflected between them forms a (defined and constant) caustic. In this case, a high intensity can be achieved in the region of the caustic's focus, leading to the generation of a nonlinear phase and spectral broadening. In other words, spectral broadening can be generated at the caustic's focus.

[0054] This spectral broadening can be complemented by generating a (smaller) nonlinearity in the nonlinear optical solid medium 22, which is achieved when the laser beam 12 passes through the nonlinear optical solid medium 22. The nonlinearity in the solid medium 22 should be chosen to be sufficiently small so that aberrations are avoided. The nonlinearity in the solid medium 22 can be adjusted, for example, by varying or setting the thickness of the nonlinear optical solid medium 22.

[0055] The first transmission area 18 can include a window 28 or be configured as a window 28. Alternatively or additionally, the second transmission area 20 can include a window 28 or be configured as a window 28.

[0056] Window 28 can be made of quartz glass or sapphire glass. Window 28 can form the nonlinear optical solid medium 22.

[0057] Window 28 may have an anti-reflective coating. The anti-reflective coating may be applied to one or both sides of window 28.

[0058] The first mirror 24 can be arranged at a distance from the chamber 16. Alternatively or additionally, the second mirror 26 can be arranged at a distance from the chamber 16.

[0059] Air can be arranged between the first mirror 24 and the chamber 16. Alternatively or additionally, air can be arranged between the second mirror 26 and the chamber 16.

[0060] Chamber 16 can be designed to be evacuated. Chamber 16 can be designed to be airless. For this purpose, chamber 16 can be coupled to a vacuum pump or a low-pressure pump.

[0061] Chamber 16 can be configured so that the gas pressure within it is adjustable. For example, the gas pressure can be increased or decreased. This can be achieved by applying overpressure and / or underpressure to chamber 16. Chamber 16 can be connected to a suitable pump or compressor for this purpose. This allows, for example, the pressure and / or type of gas or gas mixture to be varied, thereby reducing the non-linearity in the gas or gas mixture.

[0062] The gas mixture can be adjusted as desired.

[0063] The chamber 16 can comprise a base body 30. The base body 30 can be configured as a tube, in particular with a round, preferably circular, cross-section. The base body 30 can be made of metal or glass. The base body 30 configured as a tube can be gas-tightly sealed or welded at each of its two (open) ends by means of a window 28. Before the two windows 28 are attached or welded on, the base body 30 can be filled with a desired gas 14 or gas mixture.

[0064] Figure 2 shows a schematic representation of a laser arrangement 32 with the device 10 according to Figure 1. The laser arrangement 32 is set up for spectral broadening of a pulsed laser beam 12 by means of self-phase modulation.

[0065] The laser arrangement 32 comprises a laser source 34. The laser source 34 is configured to generate the laser beam 12. The propagation direction of the laser beam 12 is indicated by arrows in Figure 2.

[0066] The laser arrangement 32 comprises the device 10. The device 10 can be arranged on a base plate 11 (indicated in Figure 2 by a dashed line). The laser arrangement 32 includes a coupling optic 36 for coupling the laser beam 12 into the device 10. A suitable or desired diameter of the pulsed laser beam 12 can be set by means of the coupling optic 36. The coupling optic 36 can comprise a mode-matching telescope or be configured as a mode-matching telescope.

[0067] The laser arrangement 32 can include a mirror 37 through which the laser beam 12 can be coupled into the device 10. Alternatively, a hole can be provided in the first mirror 24 or in the second mirror 26 to couple (from behind) into the chamber 16 through the first mirror 24 or the second mirror 26, respectively.

[0068] The laser arrangement 32 includes an output coupling optic 38 for coupling the laser beam 12 out of the device 10. The output coupling optic 38 can, for example, be designed as a mirror.

[0069] The laser arrangement 32 can include a compressor 40. The compressor 40 can be configured to compress the laser beam 12 or its pulses. The compressor can be designed as a grating compressor or as a chirped mirror compressor.

Claims

Patent claims 1. Device ( 10 ) for spectral broadening of a pulsed laser beam ( 12 ) by means of self-phase modulation comprising: a chamber (16) filled with a gas (14) or gas mixture, wherein the chamber (16) has a first transmission region (18) and a second transmission region (20) for the passage of the laser beam (12) into and / or out of the chamber (16), - at least one first mirror (24), at least one second mirror (26) wherein the first mirror (24) and the second mirror (26) are arranged outside the chamber (16) and configured to reflect the laser beam (12) multiple times, in particular more than 4 times, preferably more than 10 times, between the first mirror (24) and the second mirror (26) and through the chamber (16), wherein the gas (14) causes a spectral broadening of the laser beam (12).

2. Device (10) according to claim 1, characterized in that the device (10) is configured as a multipass cell, in particular a Herriott cell or bow-tie cavity.

3. Device (10) according to claim 1 or 2, characterized in that the first transmission region (18) and / or the second transmission region (20) comprises or is formed from a nonlinear optical solid medium (22), wherein the nonlinear optical solid medium ( 22 ) causes a spectral broadening of the laser beam ( 12 ).

4. Device (10) according to claim 1 or 2, characterized in that the gas (14) in the chamber (16) is a noble gas, in particular argon, helium, krypton or xenon, or that the gas mixture in the chamber (16) comprises a noble gas, in particular argon or helium.

5. Device ( 10 ) according to one of the preceding claims , characterized in that the first mirror ( 24 ) and the second mirror ( 26 ) are arranged such that the laser beam ( 12 ) reflected between them forms a focus .

6. Device ( 10 ) according to one of the preceding claims , characterized in that the first transmission area ( 18 ) and / or the second transmission area ( 20 ) each comprise a window ( 28 ) or are each designed as a window ( 28 ).

7. Device ( 10 ) according to the preceding claim, characterized in that the window ( 28 ) is made of quartz glass or sapphire glass .

8. Device ( 10 ) according to one of the two preceding claims , characterized in that the window ( 28 ) has an anti-reflective coating .

9. Device (10) according to one of the preceding claims, characterized in that the first mirror (24) and / or second mirror (26) are each arranged at a distance from the chamber (16), in particular wherein between the first mirror (24) and air is arranged in the chamber ( 16 ) and / or between the second mirror ( 26 ) and the chamber ( 16 ).

10. Device ( 10 ) according to one of the preceding claims , characterized in that the chamber ( 16 ) is designed to be evacuatable .

11. Device ( 10 ) according to one of the preceding claims , characterized in that the chamber ( 16 ) is arranged such that a gas pressure within the chamber ( 16 ) can be adjusted .

12. Device ( 10 ) according to one of the preceding claims , characterized in that the chamber ( 16 ) has a base body ( 30 ) wherein the base body ( 30 ) is designed as a tube, in particular with a round, preferably circular, cross-section , in particular wherein the base body ( 30 ) is made of metal or glass .

13. Laser arrangement ( 32 ) for spectral broadening of a pulsed laser beam ( 12 ) by means of self-phase modulation comprising: a laser source ( 34 ) for generating the laser beam ( 12 ) , a device ( 10 ) according to one of the preceding claims , a coupling optic ( 36 ), in particular a mode-matching telescope, for coupling the laser beam ( 12 ) into the device ( 10 ), a coupling optic ( 38 ) , in particular a mirror , for coupling the laser beam ( 12 ) out of the device ( 10 ).

14. Laser arrangement ( 32 ) according to the preceding claim, characterized in that the laser arrangement ( 32 ) comprises a compressor ( 40 ), in particular a chirped mirror compressor or a grating compressor, for compression of the laser beam ( 12 ).

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