We report new experimental results on the spectral, thermal, and orientational characteristics of stoichiometry-dependent mid-IR absorption in AgGaSe(2) crystals. In currently available material, this absorption poses an obstacle to the power scaling of the 2-µm-pumped AgGaSe(2) optical parametric oscillator (OPO). Preliminary experiments have indicated that this absorption could be substantially reduced by optimization of the process parameters during crystal growth and annealing. OPO output powers approaching 10 W may be achievable by using optimized material.

Silver gallium sulfide (AgGaS2), silver gallium selenide (AgGaSe2), and silver gallium indium selenide (AgGaxIn(1 − x)Se2) are unique nonlinear crystals suitable for a wide range of three-wave mixing applications. They combine strong nonlinear coupling with phase matching across a wide (0.5 − 12.5 μm) transmission range. These properties provide the basis for CO2 laser harmonic-generator (HG), visible (VIS), and near-infrared (NIR) pumped opticalparametric-oscillator (OPO) and sumand difference-frequency-generator (SFG/DFG) systems for producing tunable laser radiation from approximately 0.65 to 12 μm. A wide range of pump lasers is now available, including diode lasers capable of direct pumping of AgGaS2 and efficient diode-pumped lasers for pumping any of these crystals. Significant progress in material characteristics and nonlinear optical (NLO) performance has been accomplished. Bulk absorption for production-quality AgGaS2 is ~0.01 − 0.02 cm across the 0.8−9-μm region. Exceptional crystals of AgGaS2 have absorption <0.0005 cm−1 at 1.064 μm, and even at 0.633 μm, absorption is ~0.015 cm−1. Figure 1 illustrates the late 1980s vintage and present transmission of AgGaS2. For AgGaSe2, absorption for production material ranges from 0.010 cm to 0.018 cm−1 from 1 μm to 11 μm. Certain crystals can have 0.007−0.008 cm−1 absorption at 10.6 μm. The NIR transmission curves for AgGaSe2 and AgGaxIn(1 − x)Se2 appear in Figure 2. This combination of optical properties, along with their good physical characteristics, make these two crystals versatile for NLO applications spanning the VIS to the infrared (ir).

The linear and second-order nonlinear optical properties of single-crystal zinc tris(thiourea) sulfate, or ZTS, are determined. The deduced nonlinear coefficients are |d(31)| = 0.31, |d(32)| = 0.35, and |d(33)| = 0.23 pm/V compared with a |d(14)| value of 0.39 pm/V for potassium dihydrogen phosphate. Because it exhibits a low angular sensitivity (deltaDeltak/deltatheta), ZTS may prove useful for type-II second-harmonic generation from 1.06 to 1.027 microm. We present the phase-matching measurement data for ZTS and compare the calculated frequency conversion efficiency for ZTS with that of several other well-characterized materials.

Room-temperature, all-solid-state, broadly tunable laser operation of Cr(2+) -doped CdSe has been demonstrated. Pumping with a Q -switched Tm, Ho:YLF laser running at a 1-kHz repetition rate achieved broadband output of 500 mW at 2.6 microm with 48% absorbed power slope efficiency. With reduced efficiency, as much as 815 mW of power was obtained. With a diffraction grating, the Cr(2+): CdSe laser was tuned from 2.3 to 2.9 microm with 10-nm bandwidth (FWHM) and output power up to 350 mW.

The intrinsic “self-trapped” hole center in KD2PO4 crystals has been identified using electron paramagnetic resonance and electron-nuclear double resonance. These defects, labeled [D2PO4]o centers, can be formed at 77 K by irradiating with either 60 kV x rays or the fourth harmonic (266 nm) of a pulsed Nd:YAG laser. The hole is equally shared by two adjacent oxygen ions, and hyperfine interactions with one phosphorus and two equivalent deuterons are observed. The sample used in this investigation was approximately 80% deuterated, thus both [D2PO4]o and [HDPO4]o centers were detected, with the former being dominant. These intrinsic self-trapped hole centers are of interest because of their potential role in the transient optical absorption produced in KD2PO4 crystals at room temperature by intense 266 nm laser pulses.