A ZnGeP>(2) (ZGP) optical parametric oscillator (OPO) with wide mid-IR tunability has been demonstrated. The singly resonant angle-tuned ZGP OPO was pumped by 100-ns erbium laser pulses at lambda =2.93mum and yielded output that was continuously tunable from 3.8 to 12.4 mum (type I phase matching) and from 4 to 10 mum (type II phase matching). An OPO pump threshold was less than 1 mJ in the whole 4-12 mum range of the output, and the quantum conversion efficiency reached 35%. An OPO linewidth was typically a few wave numbers; however, with a single intracavity etalon (uncoated Si plate) in a type II OPO it was narrowed to <0.5cm(-1). We demonstrate the sensitive detection of N(2)O gas with the narrow-linewidth OPO.

This is the experimental realization of a silver gallium sulfide (AgGaS2) optical parametric oscillator (OPO) with a wide mid-IR tuning range. The singly resonant angle-tuned AgGaS2 type-II OPO was pumped by 1.06 μm pulses from a nanosecond Nd:YAG laser and yielded idler wave continuously tunable from 3.9 to 11.3 μm with a linewidth of 1 cm−1. The OPO threshold was 0.03 J/cm2 corresponding to sub-MW/cm2 pump intensity and sub-100 μJ pump energy. The slope and absolute quantum conversion efficiencies reached 41% and 22%, respectively.

We have demonstrated optical parametric generation (OPG) in CGA crystal known for its extremely high secondorder nonlinearity (236 pm/V). A single-pass OPG was pumped by 10 lJ, 600 fs pulses at k ¼ 5 lm and the output was tunable in the 7-18 lm range. Efficient second harmonic generation of 9-11 lm radiation with an internal conversion efficiency of 62% has also been demonstrated. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 42.65.Yj; 42.79.Nv CdGeAs 2 (CGA) crystal is known for its highest second-order nonlinearity ðd eff ¼ 236 pm=VÞ among any crystals in practical use (for example, its nonlinear-optical figure of merit, d eff =n 3 , is 42 times larger than that of periodically poled lithium niobate). It transmits light between 2.4 and 18 lm and is a perfect candidate for second-harmonic generation (SHG) and nonlinear-optical frequency conversion via optical parametric oscillation (OPO), specifically into the second atmospheric window (8-12 lm). In the past, the linear absorption of as-grown CGA crystals was high ($1 cm À1 ) which precluded its wide use in nonlinear optics.Lately, it became possible, owing to the advancements in the crystal growth and after-growth processing, to produce large size CGA crystals with improved transmission [1][2][3]. As a result, highly efficient frequency doubling of CO 2 laser radiation (conversion efficiency 28% at room temperature and 50% at 77 K) [1] and difference frequency generation (at room temperature) with photon conversion efficiency >20% in the 7-20 lm spectral range [3] have been reported in CGA. Despite the fact that pulsed thresholds as low as 30 lJ are expected in a singly resonant CGA OPO, the great potential of this crystal as an OPO/OPG material has not been materialized so far. In this paper, we report the first demonstration of optical parametric generation (OPG) in CGA (which we regard as a logical step to achieving an OPO in this crystal), as well as efficient SHG operation.

The effects of 10 MeV fast electron irradiation on conductivity type, resistivity, and optical absorption of CdGeAs2 single crystals were studied. Irradiation of as-grown p-type crystals with a fluence of 1×1017 cm−2 caused compensation of the semiconductor and a marked improvement in the optical transmission. A level of absorption below 0.1 cm−1 at 5⩽λ⩽11 μm was registered. Increase in the fluence to 2×1017 cm−2 led to conversion to n-type, a drop in the resistivity and deterioration of the transmission. Analysis of the absorption in p-type crystals showed that transitions from the V2 and V3 split-off bands to the V1 valence band represent the major absorption mechanism. Splitting energies ΔE2−1=0.15 eV and ΔE3−1=0.35 eV have been calculated. Absorption in n-type crystals increased as λ2.4 indicating absorption by free electrons and their scattering by optical phonons. The effect of irradiation on the optical absorption of CdGeAs2 is assigned to the radiation-induced changes in the compensation level.