Power-scalable optical system for nonlinear frequency conversion
View Patent ↗A system for frequency conversion of laser pump radiation includes an optical element for frequency conversion of lasers or laser beams with power scalability. The element has a nonlinear birefringent, thin plate crystal. A pump beam generates frequency-shifted radiation. Phase or quasi-phase matching conditions are in the crystal between beams. Frontside and backside of the crystal have high-reflective and partially-reflective coatings, obtaining intensity enhancement of the pump and frequency-converted radiation, and maintaining relative phase delay between beams, maximizing conversion efficiency. The crystal contacts a heat sink through the high-reflective coating, minimizing temperature inhomogeneity in the crystal. Intrinsic longitudinal heat flow provides power scalability. The element, used intra-cavity, acts as a wavelength-selective component forcing laser operation on resonance of the element, maximizing frequency conversion. The wavelength selectivity allows single-frequency operation of high-power lasers with intra-cavity frequency conversion.
1. A system for frequency-conversion of a pump radiation, the system comprising:
i) a laser source generating the pump radiation;
ii) a nonlinear optical element for frequency-conversion of the pump radiation, said nonlinear optical element including a nonlinear birefringent crystal shaped as a thin plate, said thin plate having a thickness and having a front-surface and a back-surface with a size in all directions being larger than said thickness, said nonlinear optical element generating at least one frequency-converted beam as compared to a frequency of the pump radiation, and all involved beams propagating fulfilling phase matching or quasi-phase matching conditions in said nonlinear optical element;
iii) said nonlinear optical element including a partial reflective coating at said front-surface and a high-reflective coating at said back-surface of said nonlinear crystal yielding to resonant intensity enhancement of the laser pump radiation and at least one of the frequency-converted beams, said high-reflective coating being configured to reflect all involved wavelengths and to conserve or adjust a relative phase delay between the at least one frequency-converted beam and the pump radiation upon an internal reflection for maintaining the relative phase delays between various beams yielding optimal frequency-conversion;
iv) a heat sink in thermal contact with said nonlinear optical element, said heat sink having a controllable temperature enabling efficient cooling of said nonlinear crystal and generating a temperature gradient in said nonlinear crystal substantially orthogonal to said back-surface and approximatively in a direction of propagation of laser beams, and reducing a temperature inhomogeneity in said nonlinear crystal, for decreasing phase matching inhomogeneity between the various beams.
2. The system according to claim 1 , wherein said back-surface of said high-reflective coating of said nonlinear optical element is in thermal contact with said heat sink, and the temperature inhomogeneity in said nonlinear crystal is reduced in the transverse direction relative to the direction of propagation of the laser beams, for decreasing phase matching inhomogeneity between the various beams in the transverse direction.
3. The system according to claim 1 , wherein:
said nonlinear optical element provides frequency-doubling (second-harmonic generation SHG) of the laser pump radiation; and
said partial reflective coating is configured to conserve or adjust a relative phase delay between the frequency-doubled and the pump radiation upon an internal reflection within said nonlinear optical element for obtaining intensity enhancement for both the pump radiation and the frequency-doubled radiation while maintaining a relative phase delay between the pump radiation and the frequency-doubled radiation, for increasing frequency conversion.
4. The system according to claim 1 , wherein said nonlinear optical element is a mirror in an active laser resonator for a circulating pump beam.
5. The system according to claim 1 , wherein said nonlinear optical element is a mirror in a passive enhancement cavity for the laser pump beam.
6. The system according to claim 1 , wherein said nonlinear optical element is a mirror in a single-reflection configuration providing frequency-conversion for laser pulses or ns laser pulses.
7. The system according to claim 1 , wherein:
said nonlinear optical element provides frequency-halving of a pump radiation (half harmonic generation (HHG)); and
said partial reflective coating is configured to conserve or change a relative phase delay between the frequency-halved and the laser pump radiation upon an internal reflection within said nonlinear optical element, for obtaining intensity enhancement for both the pump and the frequency-halved radiation while maintaining a relative phase delay between the pump radiation and the frequency-halved radiation, for increasing frequency conversion.
8. The system according to claim 7 , wherein said nonlinear optical element is a mirror in an active laser resonator for the laser pump radiation, circulating a generated half-harmonic radiation to improve longitudinal and transverse mode selection of the half-harmonic radiation.
9. The system according to claim 7 , wherein said nonlinear optical element is a mirror in a passive enhancement cavity for the laser pump radiation, circulating the half-harmonic radiation to improve longitudinal and transverse mode selection of the half-harmonic beam.
10. The system according to claim 7 , wherein said nonlinear optical element is a mirror for a laser pump radiation in a single-reflection configuration for laser pulses or ns laser pulses, circulating the half-harmonic radiation to increase longitudinal and transverse mode selection of the half-harmonic radiation.
11. The system according to claim 7 , wherein said nonlinear optical element is a mirror in an active laser resonator for the laser pump radiation with both of said partial reflective coating and said high-reflective coating yielding a reflectivity and dispersion to generate mode-locked frequency-halved radiation.
12. The system according to claim 11 , wherein the mode-locked frequency-halved radiation has repetition rates in a 100 GHz range.
13. The system according to claim 7 , wherein said nonlinear optical element is a mirror in a passive enhancement cavity for the laser pump radiation with both of said partial reflective coating and said high-reflective coating yielding a reflectivity and dispersion to generate mode-locked frequency-halved radiation.
14. The system according to claim 13 , wherein the mode-locked frequency-halved radiation has repetition rates in a 100 GHz range.
15. The system according to claim 1 , wherein said nonlinear optical element is an optical parametric oscillator converting the laser pump radiation to a signal beam and an idler beam with both of said partial reflective coating and said high-reflective coating yielding a double-resonant intensity enhancement for the pump radiation and the idler beam.
16. The system according to claim 15 , wherein said nonlinear optical element is a mirror in an active laser resonator for the pump radiation, circulating the signal radiation to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the signal beam and indirectly for the idler beam.
17. The system according to claim 15 , wherein said nonlinear optical element is a mirror in a passive enhancement cavity for the pump radiation, and said nonlinear optical element also is a mirror in a resonator circulating the signal beam to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the signal beam and indirectly for the idler beam.
18. The system according to claim 15 , wherein said nonlinear optical element is a mirror for the laser pump beam in a single-reflection configuration, for laser pulses and ns laser pulses, and said nonlinear optical element also is a mirror within a resonator circulating the signal beam to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the signal beam and indirectly for the idler beam.
19. The system according to claim 1 , wherein said nonlinear optical element is an optical parametric oscillator converting the laser pump radiation to a signal beam and an idler beam with said partial reflective coating and said high-reflective coating yielding an intensity enhancement for both the pump beam and the signal beam.
20. The system according to claim 19 , wherein said nonlinear optical element is a mirror in an active laser resonator for the pump radiation, circulating the idler radiation to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the idler beam and indirectly for the signal beam.
21. The system according to claim 19 , wherein said nonlinear optical element is a mirror in a passive enhancement cavity for the pump radiation, circulating the idler radiation to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the idler beam and indirectly for the signal beam.
22. The system according to claim 19 , wherein said nonlinear optical element is a mirror for the laser pump radiation in single-reflection configuration, for laser pulses and ns laser pulses, circulating the idler radiation to increase a conversion efficiency and improve a longitudinal and a transverse mode selection for the idler beam and indirectly for the signal beam.