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.

Etching of 4H-SiC wafers in molten KOH as a method for micropipe and dislocation density analysis was investigated. The obtained results were correlated with those of the synchrotron white beam x-ray topography. Heavily nitrogen-doped SiC shows a significantly different etching behavior in comparison with the low-doped material. This complicates identification of different types of threading defects. In particular, it is difficult to separate Threading Screw Dislocations (TSD) from Threading Edge Dislocations (TED). Depending on the level of doping and thermal history of the crystal, some of the etch pits emerging due to the 1c screw dislocations can be as large as those due to the micropipes.