Studies of optical loss in ZGP OPO devices for near- to mid-infrared conversion

Abstract

Zinc germanium phosphide (ZGP) is well suited to use in optical parametric oscillators (OPOs) for conversion of near-infrared laser output into the mid-infrared waveband (3 to 5 µm). Typical OPO applications seek to exploit pump wavelengths close to 2 µm so that both the output wavelengths fall within the mid-infrared waveband. However, the material typically suffers optical loss arising from growth defects that becomes significant at wavelengths below about 2.5 µm. We report the results of calorimetric studies that show that the loss can comprise both absorptive and scattering components. We have assessed the affect of loss at the pump wavelength on the conversion efficiency of a high pulse repetition frequency, doubly-resonant, ZGP OPO pumped with 2.094 µm radiation generated by a wavelength doubled Nd:YLF laser. The OPO used crystals having loss coefficients in the range 0.03 cm -1 to 0.3 cm -1 . The reduction in slope efficiency for the conversion process was evaluated over a range of pump beam diameters (1/e 2 intensity) from 0.12 mm to 0.30 mm. For the largest beam diameter a slope efficiency of 57 % was measured for a ZGP OPO crystal having a loss coefficient of 0.03 cm -1 . The slope efficiency reduced to about 30 % when the loss coefficient was increased to 0.3 cm -1 .

Optical parametric amplification of mid-infrared radiation using multi-layer glass-bonded QPM GaAs crystals

“…To demonstrate optical parametric amplification within the GBGaAs stacks a 2 µm pumped doubly-resonant Type I ZGP OPO was configured for mid-IR generation at 3.8 and 4.7 µm [7] . The 2.094 µm pump beam was generated in a walk-off compensated Type II degenerate KTP OPO, which was itself pumped by a high repetition-rate (10 kHz) Qswitched diode-pumped Nd:YLF laser operating at 1.047 µm.…”