High-energy 1064-nm pumped optical parametric oscillator for the 6 µm spectral range based on HgGa2S4

Abstract

The defect chalcopyrite crystal HgGa 2 S 4 has been employed in a 1064-nm pumped optical parametric oscillator to generate <7 ns long idler pulses near 6.3 µm with energies as high as 3 mJ, tunable in a broad spectral range from 4.5 to 9 µm.

Progress in 1-μm Pumped Mid-IR Optical Parametric Oscillators Based on Non-Oxide Nonlinear Crystals

“…Nevertheless, the focal fluences that could be achieved with the improved idler beam quality are much higher compared to the results in Fig. 4b [41]. For instance, assuming a collimated idler beam at 6.3 µm with a diameter of 0.5" focused by a 100 mm lens, axial focal fluence of 2 J/cm 2 is calculated both for 2.25 and 5.35 mm pump diameters with the RISTRA output energies.…”

“…For instance, assuming a collimated idler beam at 6.3 µm with a diameter of 0.5" focused by a 100 mm lens, axial focal fluence of 2 J/cm 2 is calculated both for 2.25 and 5.35 mm pump diameters with the RISTRA output energies. This value is only 0.2 J/cm 2 for the large Fresnel number linear cavity in [41] where the output energy reached 3 mJ but M 2~3 0, see Fig. 4b.…”

“…Recently the performance of HGS based OPOs was greatly improved using a diode-pumped laser for pumping at 1064 nm [39,41]. The pump system comprised a Q-switched Nd:YAG laser and amplifier, with a linewidth of 30 GHz (1 cm -1 ) and M 2 factor of ~1.4.…”

“…The pump source was the same as used before with HGS at 10 Hz [41], see Fig. 4b, with 8 ns pulse duration, but to improve the spatial beam profile (eliminate diffraction rings producing hot spots) a vacuum diamond pinhole was installed in the focus of a telescope.…”

HgGa2S4–based RISTRA OPO pumped at 1064 nm

“…Obviously some of the prerequisites, on the first place the absent spatial walk-off in the 90°-phase-matchable CSP, were not satisfied in this experiment. Therefore, we decided to examine the RISTRA concept with the most promising non-oxide mid-IR crystal for 1-µm pumped OPOs, HgGa 2 S 4 (HGS), with which we obtained idler energy of 3 mJ at ~6.3 µm with a linear cavity [4]. Here we compare RISTRA cavity with linear and ring cavities whose parameters are as close as possible and investigate the effect of the spatial walk-off by changing the pump beam diameter.…”