Optical parametric generation in CGA crystal

Abstract

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.