RECENT PROGRESS IN TUNABLE NONLINEAR-OPTICAL DEVICES FOR INFRARED-SPECTROSCOPY

A laser source based on difference-frequency generation (DFG) in AgGaS 2 has been developed for high resolution IR kinetic spectroscopy (IRKS ) of free radicals. Continuously tunable radiation has been generated between 4 and 9 mu m (2500-1100 cm(-1)) by mixing two cw single-mode d ye/Ti:Al2O3 lasers in a 90 degrees type I phasematching configuration. Spectra of the free radicals HOCO, DOCO and HCCN were obtained by usi ng this source. Concurrently, the suitability of III-V single-mode cw diode lasers for DFG of tunable IR radiation has been explored by mixi ng two laser diodes (808 and 690 nm) in AgGaS2 (IR power generated app roximate to 3 nW). Techniques to increase the IR DFG power level such as the use of high-power optical semiconductor amplifiers or an extern al build-up cavity for the nonlinear crystal have been investigated. A s much as 50 mu W of cw IR radiation, tunable near 4.3 mu m have been generated by mixing a high-power tapered semiconductor amplifier at 85 8 nm and a Ti:Al2O3 laser in AgGaS2. Recent progress in generating cw IR radiation near 3.2 mu m by mixing an extended-cavity diode laser ne ar 795 nm and a compact diode-pumped Nd:YAG laser in AgGaS2 with an ex ternal enhancement cavity is also described.