Nonlinear optical converter

Abstract

The present invention relates to a nonlinear optical converter (11) for a laser radiation source comprising a pump laser for generating a pump laser beam, comprising a first optical parametric oscillator (OPO) crystal (2) facing the pump laser, which is configured to generate two first amplification bands, in particular a signal band and an idler band, as well as a residual pump radiation from the pump laser beam (6) and has a first phase adjustment angle (7), further comprising a second optical parametric oscillator (OPO) crystal (3) downstream of the first optical parametric oscillator (OPO) crystal (2), which is configured to generate two further second amplification bands, in particular a signal band and an idler band, from the residual pump radiation.

Description

[0001] The present invention relates to a nonlinear converter for a laser radiation source, in particular for a spectroscope or an optronic countermeasures system, and to such a laser radiation source, in particular for a spectroscope or an optronic countermeasures system.

[0002] A nonlinear converter is based on the concept that processes occur in nonlinear optical materials under intense laser radiation, causing the wavelength of the incident light to change. Using optical parametric generation, laser light with a tunable wavelength can be generated from fixed-frequency pump lasers.

[0003] In such laser applications, it is necessary to implement a compact and robust laser source that can generate and selectively emit a desired, time-varying average power and pulse energy (modulation) according to an electronic input signal. Infrared laser beams in the atmospheric transmission window range of around 2 µm and in the range of 3-5 µm are particularly required.

[0004] An optronic countermeasure is a defense mechanism designed to target sensors or guidance systems based on optical or infrared technology. This defense mechanism aims to reduce or neutralize the effectiveness of optical and infrared sensors used in guided missiles, reconnaissance, and surveillance equipment.

[0005] Nonlinear converters are generally known. For example, Espen Lippert et al. published a paper entitled “A 22-watt mid-infrared optical parametric oscillator with V-shaped 3-mirror ring resonator” in Optics Express on December 2, 2010, describing an optical parametric oscillator (OPO) used for power scaling of coherent mid-infrared (MWIR) sources. This OPO employs a V-shaped 3-mirror ring resonator that allows two passes of the beams through a nonlinear OPO crystal to achieve an output power of 22 W.

[0006] To improve spectral coverage, US 9,599,875 B2 discloses an OPO that can generate five separate beams from a single pump input beam. Each beam is aligned along a single beamline and has a different color and wavelength than the others. This is achieved by using a V-shaped resonator that generates four mid-IR wavelengths, namely two mid-IR wavelength pairs (signal and idler, respectively), by employing different phase-matching angles on the forward and return paths through the OPO crystal.

[0007] The arrangement according to US 9,599,875 B2 has proven disadvantageous because the two mid-IR wavelength pairs cannot be independently adjusted, as they are in a fixed relationship to each other. Furthermore, since the OPO crystal is rotated in the critical plane, the point of impact on the output coupler shifts, which has proven problematic. Additionally, the precision in spectral analyses and high-resolution measurements is limited, particularly due to this lack of flexibility.

[0008] One object of the present invention is to overcome the disadvantages of the prior art, in particular to provide a more flexible and / or more precise nonlinear converter that has improved efficiency and / or is simplified in design and covers a high spectral bandwidth in the infrared range.

[0009] This problem is solved by the subject matter of the independent claim.

[0010] This application provides a nonlinear optical converter for a laser radiation source, particularly for a spectroscope or an optronic countermeasures system, which includes a pump laser for generating a pump laser beam. For the purposes of this application, a nonlinear converter is understood to be an optical component that utilizes the nonlinear optical properties of a material to change the wavelength or frequency of light. A pump laser is understood to be a laser used as an energy source to excite another laser medium, thereby enabling laser emission from that medium. This energy transfer is referred to as "pumping".

[0011] The nonlinear optical converter according to the invention comprises a first optical parametric oscillator (OPO) crystal facing the pump laser, which is configured to generate two first gain bands, in particular a signal band and an idler band, from the pump laser beam and has a first phase-matching angle. According to the present application, an OPO is understood to be a nonlinear optical device that splits the light from a pump laser into two lower frequencies, in particular a signal and an idler band, which satisfy the energy conservation principle. ωpump=ωsignal+ωidler; where ω pump the frequency of the pump laser beam, ω signal the frequency of the generated signal wave and ω idler The frequency of the generated idler wave is denoted. The phase adjustment angle refers to the angle at which the light waves are propagated within the OPO to enable efficient interaction.

[0012] In other words, the first OPO crystal generates two first amplification bands from the pump laser beam, typically a signal band and an idler band. The downstream second OPO crystal uses the residual pump radiation from the first crystal to generate two further second amplification bands. It can be advantageous if the emitted radiation of the two first amplification bands partially overlaps spectrally with the two second amplification bands of the second crystal. This allows, for example, the generation of a broad, continuous amplification band for both signal and idler, which would not be achievable with a single crystal.

[0013] According to the invention, the converter comprises a second optical parametric oscillator (OPO) crystal downstream of the first OPO crystal. This second OPO crystal is configured to generate two further amplification bands, in particular a signal band and an idler band, from the residual pump radiation after the first crystal. This allows for the generation of a broad emission spectrum, particularly from five wavelength ranges, with a low number of optical components in the mid-infrared range, especially in the region of the atmospheric transmission windows around 2 µm and in the 3-5 µm range. This enables more efficient use of the pump energy and extended spectral coverage. Due to the cascaded connection of two OPO crystals, the converter according to the invention is significantly more adaptable and, with regard to…The output radiation is adjustable, as the converter can be designed so that the OPO crystals can be individually oriented and selected.

[0014] According to an exemplary embodiment of the present invention, the second optical parametric oscillator (OPO) crystal has a second phase-adjustment angle that differs from that of the first OPO crystal. The phase-adjustment angle is a critical parameter in nonlinear optical processes because it affects the efficiency of the frequency conversion. By varying the phase-adjustment angle in the second OPO crystal compared to the first, additional flexibility in the generation of the gain bands is achieved. The different phase-adjustment angles in the OPO crystals contribute to a better match between the generated wavelengths and the atmospheric transmission windows, thus increasing the efficiency and effectiveness of the laser source.Another advantage of this arrangement is the partial compensation of the walk-off effect, which occurs in nonlinear optical processes with birefringence phase matching and can impair the efficiency of the frequency conversion. By selectively varying the phase matching angles, this effect can be reduced or minimized, leading to improved efficiency, especially with small pump jet diameters.

[0015] According to an exemplary embodiment of the present invention, the second optical parametric oscillator (OPO) crystal has a phase matching condition that differs from that of the first OPO crystal, achieved, for example, by changing the crystal temperature. Matching the phase matching condition between the two OPO crystals can enable more precise control of the generated gain bands. The term "phase matching condition" refers to the specific parameters required to achieve phase matching in a nonlinear crystal. By varying the crystal temperature, the phase matching condition can be selectively modified. The ability to vary the phase matching condition by changing the temperature provides a flexible and precise method for controlling the output radiation without the need for mechanical modifications or additional optical components.This contributes to a more compact and stable design of the optical converter.

[0016] According to an exemplary embodiment of the present invention, the angular difference between the first and second phase-matching angles is in the range of 0.05° to 20°, in particular from 0.1° to 15° or up to 11°. This specific arrangement of the phase-matching angles between the two optical parametric oscillator (OPO) crystals enables targeted control of the generated gain bands. The angular difference between the phase-matching angles of the two crystals leads to an additional spectral broadening of the generated wavelengths. This configuration allows for particularly effective compensation of the walk-off effect.

[0017] By selectively varying the phase-matching angles, the efficiency of the nonlinear conversion process can be improved, resulting in higher output power and better matching to the atmospheric transmission windows. This matching is crucial for optimizing laser beams in the atmospheric transmission window range around 2 µm and in the 3–5 µm range. The option of arranging the crystals in a V-resonator or a non-planar ring resonator offers additional flexibility in the design of the optical converter and allows for further optimization of the spectral properties and conversion efficiency.

[0018] According to an exemplary embodiment of the present invention, the first and second OPO crystals are movably mounted such that their phase-matching angles can be varied. This movable mounting allows for fine-tuning of the crystals' phase-matching angles, enabling flexible adjustment of the generated gain bands. The ability to vary the phase-matching angles also contributes to the stability and flexibility of the system, as it provides a simple way to adjust the system parameters without physically altering the OPO crystals or the resonator. This results in greater adaptability of the system to different operating conditions and requirements, thus expanding the application possibilities of the nonlinear optical converter.

[0019] According to an exemplary embodiment of the present invention, the first and second optical parametric oscillator (OPO) crystals are mounted so that they can be moved independently of one another, allowing their phase-matching angles to be varied independently. This means that each of the two OPO crystals is able to change its position or orientation independently of the other in order to achieve the optimal phase-matching angle. Due to the independent movement of the two crystals, each crystal can be individually adjusted, and no complex, structural solution is required to couple the OPO crystals for their joint adjustment. In this respect, the wavelength tuning in the nonlinear optical converter is improved. Wavelength tuning can be understood as the ability to continuously or discretely change the wavelength (or frequency) of the emitted light from an optical device.

[0020] According to an exemplary embodiment of the present invention, the nonlinear optical converter comprises a linear or ring resonator containing both the first and the second optical parametric oscillator crystals, wherein these crystals are oriented to avoid the walk-off effect, in particular such that they have different phase matching. The walk-off effect can impair the efficiency of the beam conversion by reducing the spatial overlap of the pump beams and the generated signal and idler beams. By selectively orienting the OPO crystals with different phase matching angles, this effect is at least partially compensated. Different phase matching means that the crystals are aligned such that they, and in particular their optical axes, are oriented at different angles to the pump beam.

[0021] According to an exemplary embodiment of the present invention, the nonlinear optical converter comprises a V-resonator having the first optical parametric oscillator crystal and the second optical parametric oscillator crystal oriented such that a phase-matching plane of an OPO crystal is inclined with respect to a ring plane of the V-resonator, in particular arranged substantially perpendicular to it. The V-resonator represents a special resonator geometry characterized by its V-shape, which enables efficient use of the nonlinear crystals. The phase-matching plane refers to the plane in the resonator in which the phase matching between different wavelengths or frequencies of light takes place.The ring plane refers to the geometric plane of the beam path in a V-resonator, where the optical beam is reflected in a V-shaped arrangement and can be guided back and forth by means of several deflecting mirrors. In this arrangement, it is easy to rotate the crystals in their phase-matching plane to vary the generated spectrum without affecting the stability of the resonator. A further advantage is that the V-shape of the resonator achieves an effective double pass through each crystal, which increases conversion efficiency and reduces the length of the required crystals. This contributes to a more compact and robust design of the laser system.

[0022] In an exemplary embodiment of the present invention, the length of the first and / or the second optical parametric oscillator (OPO) crystal in the beam propagation direction is less than 15 mm, in particular less than 12 mm or less than 10 mm. This allows the crystals to be designed more compactly. Shorter crystals can help to minimize dispersion effects and thus improve the coherence and spectral purity of the generated radiation. Furthermore, reducing the crystal length can decrease the manufacturing costs and the complexity of the system. It can be advantageous to choose the first OPO crystal to be shorter than the second OPO crystal.This allows the relative gain between the two crystals to be equalized, since otherwise the gain in the first crystal would be higher than in the second crystal due to a higher pumping intensity at the same length, which receives a lower pumping intensity due to the conversion in the first crystal.

[0023] According to an exemplary embodiment of the present invention, a phase-matching condition in the first optical parametric oscillator (OPO) crystal and in the second optical parametric oscillator (OPO) crystal is selected such that the two first gain bands are spectrally further away from a degeneration wavelength of the first optical parametric oscillator (OPO) crystal than the two second gain bands are with respect to a degeneration wavelength of the second optical parametric oscillator (OPO) crystal (3). Alternatively, the phase-matching condition in the first crystal can be selected such that the first gain bands are spectrally further away from the degeneration wavelength of the OPO, while the phase-matching condition in the second crystal is selected such that the second gain bands are closer to the degeneration wavelength.The degeneracy wavelength refers to the wavelength of light at which the frequencies of the generated signal and idler beams are equal, meaning these two beams have identical wavelengths. Therefore, at the same pumping intensity, the first crystal has a lower relative gain than the second crystal, so that during operation the drop in pumping intensity in the first crystal can be partially compensated for by conversion. This allows the relative gain between the two crystals to be matched.

[0024] Another advantage is that shorter crystals can offer higher mechanical stability and robustness.

[0025] According to an exemplary embodiment of the present invention, the nonlinear optical converter comprises a ring resonator having both the first optical parametric oscillator crystal and the second optical parametric oscillator crystal. A ring resonator is a special type of optical resonator characterized by a ring-shaped arrangement of mirrors or other reflective elements that cause the light to circulate in a closed path. This configuration allows the light to pass through the nonlinear crystals multiple times, thus increasing the efficiency of nonlinear processes such as optical parametric oscillation. The conversion efficiency can be increased by means of a ring resonator.Furthermore, a more compact design can be achieved using a ring resonator, as the length of the optical path is effectively extended without having to increase the physical size of the system accordingly.

[0026] According to an exemplary embodiment of the present invention, the ring resonator is non-planar. For example, the ring resonator includes a deflecting mirror which does not lie in the plane spanned by the first and second optical parametric oscillator crystals. The term "non-planar" can be understood to mean that the ring resonator has a three-dimensional structure, wherein the optical components and / or the beam path through the resonator are not all arranged in a single plane. The non-planar structure of a ring resonator allows for the simpler integration of additional optical elements, such as further deflecting mirrors or lenses, without increasing the overall size of the setup. It can also generate image rotation in the direction of rotation, which improves the stability, beam quality, or symmetry of the output beam.

[0027] According to a further aspect of the present invention, which can be combined with the preceding aspects and exemplary embodiments, a laser radiation source is provided, particularly for a spectroscope or an optronic countermeasures system. The laser radiation source comprises a pump laser and a nonlinear optical converter according to the invention. The pump laser serves as the primary radiation source and generates a pump laser beam that is fed into the nonlinear optical converter. This converter consists of at least two optical parametric oscillator (OPO) crystals connected in series. The first OPO crystal is configured to split the pump laser beam into two first amplification bands, namely a signal band and an idler band.These two bands are then directed into the second OPO crystal, which in turn splits two further, secondary amplification bands from the remaining pump radiation, resulting in a total of four additional amplification bands. A significant advantage of this configuration is the generation of a particularly broad emission spectrum in the mid-infrared range, in order to optimally match the generated amplification bands to the atmospheric transmission windows, especially in the region around 2 µm and in the 3–5 µm range.

[0028] According to a further aspect of the present invention, which can be combined with the preceding aspects and exemplary embodiments, a method for generating laser radiation in the infrared range, in particular in the range of the atmospheric transmission windows around 2 µm and / or in the range of 3 µm to 5 µm, is provided by means of a laser radiation source designed according to one of the previously described aspects and / or exemplary embodiments.

[0029] Preferred embodiments are specified in the dependent claims.

[0030] Further properties, features and advantages of the invention will be clarified below by describing preferred embodiments of the invention with reference to the accompanying exemplary drawings, which show: Fig. 1 schematically an embodiment of a nonlinear optical converter with a linear resonator and two optically parametric oscillator crystals; Fig. 2a schematically an embodiment of a nonlinear optical converter with a V-resonator and two optically parametric oscillator crystals in side view; Fig. 2b schematically the embodiment according to Fig. 2a in top view; Fig. 3a schematically an embodiment of a V-resonator with two optically parametric oscillator crystals in side view; Fig. 3b schematically the embodiment according to Fig. 3a in top view; and Fig. Figure 4 schematically shows an embodiment of a non-planar ring resonator with two optically parametric oscillator crystals.

[0031] In the following description of exemplary embodiments of the invention, a nonlinear optical converter according to the invention is generally designated by reference numeral 11. Identical or similar components are designated by the same or similar reference numerals.

[0032] Fig. Figure 1 shows a schematic representation of a nonlinear optical converter 11, which includes a pump laser that generates a pump laser beam 6. The in Fig. The converter 11 shown in Figure 1 has a linear resonator comprising a first optical parametric oscillator (OPO crystal 2) and a second OPO crystal 3 downstream of it in the beam propagation direction, as well as an input coupling mirror 1 and an output coupling mirror 4, through which an output radiation 5 is emitted. The OPO crystals 2 and 3 are arranged at a specific angle to each other to optimize phase matching and minimize the walk-off effect.

[0033] The first OPO crystal 2 has a first phase matching angle 7 and is configured to generate two first amplification bands from the pump laser beam 6, in particular a signal band and an idler band. A second OPO crystal 3 is arranged downstream of the first OPO crystal 2. This second OPO crystal 3 has a second phase matching angle 8 that differs from the first phase matching angle 7, or it has a phase matching condition that is otherwise modified compared to crystal 2, for example, a different temperature. This second OPO crystal 3 is configured to generate two further second amplification bands from the residual pump radiation of the first OPO crystal, in particular a signal band and an idler band. The output coupler 4 is arranged at the end of the resonator and couples the generated output beam 5 out of the resonator.Thus, a broad emission spectrum, particularly consisting of five wavelengths, can be generated with a low number of optical components in the mid-infrared range, especially in the region of the atmospheric transmission windows around 2 µm and in the 3-5 µm range. The pump energy can be used efficiently to create extended spectral coverage. Due to the series connection of two OPO crystals 2, 3, the converter 11 according to the invention is significantly more flexible and adjustable with respect to the output radiation, since the converter can be designed in such a way that the OPO crystals can be individually oriented and selected.

[0034] The execution according to the Fig. 2a and Fig. Figure 2b shows an alternative embodiment of the nonlinear optical converter 11, in which a V-resonator is used. In this arrangement, the first OPO crystal 2 and the second OPO crystal 3 are arranged in a V-shaped resonator, which, in addition to the coupling mirror 1, has a deflecting mirror 1'. This configuration allows a double effective passage through the OPO crystals 2, 3, resulting in more efficient conversion and making it possible to reduce, in particular halve, the lengths of the OPO crystals 2, 3 compared to a corresponding embodiment as a linear resonator. The V-shaped beam path is shown in particular from the top view according to Figure 2b. Fig. 2b is shown.

[0035] In all illustrated embodiments, the use of at least two OPO crystals with different phase-matching angles achieves broad spectral emission in the mid-infrared range. This is particularly advantageous for creating broad spectral coverage in the desired mid-IR range with minimal optical component usage.

[0036] The embodiment according to the Fig. 3a, Fig. 3b differs from the embodiment according to the Fig. 2a, Fig. 2b essentially through the beam path, which is achieved by individually adjusting the phase adjustment angles 7, 8 of the OPO crystals 2, 3. The first and the second optical parametric oscillator (OPO) crystals 2, 3 are mounted so that they can be moved independently of each other, allowing their phase adjustment angles 7, 8 to be set independently. This enables each of the two OPO crystals 2, 3 to change its position or orientation independently of the other in order to set the optimal phase adjustment angle 7, 8. This is evident from a comparison of the Fig. 3a, Fig. 3b and the Fig. 2a, Fig. Figure 2b highlights the different phase adjustment angles 7, 8 and the resulting beam path, indicated by reference symbol 5. This allows the spectrum to be varied without affecting the resonator stability.

[0037] Fig.Figure 4 shows a further embodiment of the nonlinear optical converter 11 in the form of a nonplanar ring resonator. Compared to the previous embodiments, the ring resonator includes two additional deflecting mirrors 9, 10, which cause the light to circulate in a closed path 12 in order to guide the light multiple times through the nonlinear crystals 2, 3.

[0038] The deflecting mirror 10 is not located in the plane spanned by the OPO crystals 2,3 and the deflecting mirror 9, so that the ring resonator is non-planar.

[0039] In all embodiments, at least two nonlinear crystals 2, 3 connected in series are used in an OPO resonator with different phase matching angles 7, 8 relative to the pump radiation 6 in the different crystals. This creates additional amplification spectra, which are used by the resonator to generate multiple output wavelengths. It is particularly advantageous to incorporate the crystals 2, 3 in a manner comparable to walk-off compensation, but explicitly not to use the exact inverse alignment used in such compensation (identical phase matching in both crystals 2, 3), but rather to use the downstream crystal 3 with an angular difference relative to the first crystal 2.Explicit alignment can be utilized if, according to the invention, the phase matching condition in the second OPO crystal 3 is modified, for example, by changing the crystal temperature of the second OPO crystal 3. This results not only in the desired spectral broadening but also in partial or even exact compensation of the walk-off effect, which improves efficiency, particularly at small pump jet diameters. A significant advantage of the present invention is the possibility, arising from the use of two separate crystals 2, 3, of individually adjusting their phase matching angles 7, 8 in order to achieve optimal tuning and effective, flexible variation of the spectrum without impairing resonator stability.

[0040] The features disclosed in the foregoing description, figures and claims can be important for the realization of the invention in its various embodiments, both individually and in any combination. Reference symbol list 1 coupling mirror 1' Deflection mirror 2 first OPO crystal 3 second OPO crystal 4 coupling mirrors 5 Output beam 6 Pump laser beam 7 first phase adjustment angle 8 second phase adjustment angle 10 deflecting mirrors 11 Nonlinear optical converter 12 Path c optical axis QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 9,599,875 B2 [0006, 0007] Cited non-patent literature

[0000] Espen Lippert et al. on December 2, 2010 in Optics Express a publication entitled "A 22-watt mid-infrared optical parametric oscillator with V-shaped 3-mirror ring resonator"

[0005]

Claims

Nonlinear optical converter (11) for a laser radiation source comprising a pump laser for generating a pump laser beam, comprising a first optical parametric oscillator (OPO) crystal (2) facing the pump laser, which is configured to generate two first amplification bands, in particular a signal and an idler band, as well as a residual pump radiation from the pump laser beam (6) and has a first phase adjustment angle (7), characterized by a second optical parametric oscillator (OPO) crystal (3) downstream of the first optical parametric oscillator (OPO) crystal (2), which is configured to generate two further second amplification bands, in particular a signal and an idler band, from the residual pump radiation. Nonlinear optical converter (11) according to claim 1, wherein the second optical parametric oscillator (OPO) crystal (3) has a second phase adjustment angle that differs from the first phase adjustment angle (7). Nonlinear optical converter (11) according to claim 1 or 2, wherein the second optical parametric oscillator (OPO) crystal (3) has a second phase matching condition that differs from the first OPO crystal (2), for example by a changed crystal temperature. Nonlinear optical converter (11) according to claim 2, wherein the angular difference between the first and the second phase adjustment angle (8) is in the range of 0.05° to 20°, in particular 0.1° to 15° or up to 11°. Nonlinear optical converter (11) according to one of the preceding claims, wherein the first and the second optical parametric oscillator (OPO) crystal (3) are mounted in such a way that their phase adjustment angles are variable. Nonlinear optical converter (11) according to claim 5, wherein the first and the second optical parametric oscillator (OPO) crystal (3) are mounted in such a way as to be movable independently of each other that their phase adjustment angles can be varied independently of each other. Nonlinear optical converter (11) according to one of the preceding claims, further comprising a linear or ring resonator comprising the first optical parametric oscillator (OPO) crystal (2) and the second optical parametric oscillator (OPO) crystal (3) which are oriented to avoid the walk-off effect, in particular such that they have different phase matching. Nonlinear optical converter (11) according to one of the preceding claims, further comprising a V-resonator having the first optical parametric oscillator (OPO) crystal (2) and the second optical parametric oscillator (OPO) crystal (3) oriented such that a phase matching plane of an OPO crystal is inclined with respect to a ring plane of the V-resonator, in particular arranged substantially perpendicular thereto. Nonlinear optical converter (11) according to claim 8, wherein the length of the first and / or the second optical parametric oscillator (OPO) crystal (2, 3) in the beam propagation direction is less than 15 mm, in particular less than 12 mm or less than 10 mm. Nonlinear optical converter (11) according to one of the preceding claims, wherein a length of the first OPO crystal (2) is shorter than a length of the second OPO crystal (3). Nonlinear optical converter (11) according to one of the preceding claims, wherein a phase matching condition in the first optical parametric oscillator (OPO) crystal (2) and in the second optical parametric oscillator (OPO) crystal (3) are selected such that the two first gain bands are spectrally further away from a degeneracy wavelength of the first optical parametric oscillator (OPO) crystal (2) than the two second gain bands with respect to a degeneracy wavelength of the second optical parametric oscillator (OPO) crystal (3). Nonlinear optical converter (11) according to one of the preceding claims, further comprising a ring resonator comprising the first optical parametric oscillator (OPO) crystal (2) and the second optical parametric oscillator (OPO) crystal (3). Nonlinear optical converter (11) according to claim 12, wherein the ring resonator is nonplanar, in particular having a deflecting mirror (1') which does not lie in a plane spanned by the first and the second optical parametric oscillator (OPO) crystal (3). Laser radiation source comprising a pump laser and a nonlinear optical converter (11) designed according to one of the preceding claims.

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