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DE-102024004475-A1 - Nonlinear optical converter

DE102024004475A1DE 102024004475 A1DE102024004475 A1DE 102024004475A1DE-102024004475-A1

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.

Inventors

  • Marc Eichhorn
  • Christelle Kieleck
  • Madeleine Eitner
  • Dominik Lorenz

Assignees

  • Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung eingetragener Verein

Dates

Publication Date
20260513
Application Date
20241108

Claims (14)

  1. 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), 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 band and an idler band, from the residual pump radiation.
  2. 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).
  3. 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.
  4. Nonlinear optical converter (11) according to Claim 2 , wherein the angle 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°.
  5. 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.
  6. Nonlinear optical converter (11) according to Claim 5 , wherein the first and the second optical parametric oscillator (OPO) crystal (3) are mounted so that they can be moved independently of each other, and their phase adjustment angles can be varied independently of each other.
  7. 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.
  8. 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.
  9. 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.
  10. 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).
  11. 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).
  12. 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).
  13. Nonlinear optical converter (11) according to Claim 12 , wherein the ring resonator is non-planar, 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).
  14. Laser radiation source comprising a pump laser and a nonlinear optical converter (11) designed according to one of the preceding claims.

Description

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. 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. 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. 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. Nonlinear converters are generally known. For example, published 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" , in which an optical parametric oscillator (OPO) is described that is used for power scaling of coherent mid-infrared (MWIR) sources and uses 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. To improve spectral coverage, the US 9,599,875 B2 An OPO capable of generating five separate beams from a single pump input beam, each aligned along a single beam path (i.e., aligned with one another) and exhibiting a different color and wavelength than the other beams. This is achieved by using a V-shaped resonator that generates four mid-IR wavelengths, specifically two mid-IR wavelength pairs (signal and idler each), by employing different phase-match angles on the forward and return paths through the OPO crystal. The order according to the US 9,599,875 B2 It has proven disadvantageous that the two mid-IR wavelength pairs cannot be adjusted independently, as they are fixed in relation to each other. Furthermore, because 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. 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. This problem is solved by the subject matter of the independent claim. 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". 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 denotes 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. The phase matching angle refers to the angle at which the light waves are propagated within the OPO to enable efficient interaction. 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