AgGaGeS 4 (AGGS) is a promising nonlinear crystal for mid-IR laser applications which could fulfill the lack of material able to convert a 1.064 µm pump signal (Nd:YAG laser) into wavelengths higher than 4 µm up to 11 µm. The processing steps of this material are presented in this study. The key issue of AGGS crystal processing is the control of decomposition at high temperature due to the high volatility of GeS 2. This study present the solutions to obtain high quality single crystal. AGGS crystals with 28 mm diameter and 70 mm length were grown by the Bridgman-Stockbarger method. The crystals have good homogeneity and high transparency in the 0.5-11.5 µm spectral range making it suitable for optical experiments. The influence of GeS 2 volatility on melt stoichiometry during the AgGaGeS 4 processing is outlined and solutions to improve the crystals quality are presented.

We demonstrate a nanosecond single-frequency nested cavity optical parametric oscillator (NesCOPO) based on orientation-patterned GaAs (OP-GaAs). Its low threshold energy of 10 μJ enables to pump it with a pulsed single-frequency Tm:YAP microlaser. Stable single-longitudinal-mode emission is obtained owing to Vernier spectral filtering provided by the dual-cavity doubly-resonant NesCOPO scheme. Crystal temperature tuning covers the 10.3-10.9 μm range with a quasi-phase-matching period of 72.6 μm. A first step toward the implementation of this device in a differential absorption lidar is demonstrated by carrying out short-range standoff detection of ammonia vapor around 10.4 μm. Owing to the single-frequency emission, interferences due to absorption by atmospheric water vapor can be discriminated from the analyte signal.

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We demonstrate optical parametric amplification in ZnGeP(2) (ZGP) of the radiation emitted by a single-frequency continuous-wave quantum cascade laser (QCL) in the range 7.8-8.4 μm. The ZGP amplifier is pumped by a single-frequency parametric source at 2210 nm. For a pump energy of 6 mJ, we report an average gain of 50 over this range and a maximum gain of 111 for 7.5 mJ. An exponential trend is observed when changing the pump energy, with very good agreement with theory. These features are of valuable interest for increasing the standoff detection range of hazardous chemicals and explosives by QCL-based backscattering spectroscopy systems.

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