Recent advances in continuously tunable 8-12 mu m radiation using optical parametric oscillators

Advances in the development of crystals with good nonlinear properties have made optical parametric oscillators (OPOs) strong candidates for generation of coherent radiation. These technological advancements have renewed research in the development of solid state 8 - 12 mu m coherent OPO LIDAR sources for remote chemical sensing applications, if millijoule pulse energies are adequate and short (ns) pulses are beneficial. We present recent advances in OPO technology that have generated tunable, 3 - 5 mu m and 8 - 12 mu m radiation. Specific pump source technologies to be addressed are CO2, Nd:YAG, Er and Ho:host materials. The paper will examine nonlinear materials such as ZnGeP2, AgGaSe2, AgGaS2, and CdSe and their relevant parameters. The authors will discuss their results to obtain millijoule/pulse OPO energies with two different pump sources. Using a 25 mi, 50 ns, 2.79 mu m Cr,Er:YSGG laser to pump CdSe and ZnGeP2 OPOs, signal wavelengths from 3.6 - 4.7 mu m and idler wavelengths from 6.9 - 12.7 mu m were generated. A CdSe OPO yielded a 59% slope efficiency (eta) and 1.2 - 2.4 mi idler output between 8.5 and 12.3 mu M. A ZnGeP2 OPO operated with a lower threshold, eta = 29%, and 0.7 - 2.4 mi idler output from 6.9 to 9.9 mu M. Secondly, a non-critically phase-matched KTP OPO, at the fixed wavelength of 1.57 mu m, was used to pump a type I AgGaSe2 OPO. A 6.5 mm x 6.5 mm x 35.3 mn long, AgGaSe2 crystal yielded output, tunable from 6 to 14 mu m, with energies of up to 1.2 ml/pulse and a bandwidth of similar to 5 cm(-1) (FWHM).