Compact, broadly tunable, mid-IR source for the spectroscopic investigation of molecular reference lines in the 27-to 33-THz range

We report on the improvement of a tunable, high resolution, diode laser-bas ed, difference-frequency spectrometer using an AgGaS2 nonlinear crystal. We use a type-II cut crystal as a part of the improvement compared with a typ e-I cut, which was used in our preliminary setup [1], [2]. The two tunable laser diodes are operating near lambda(3) = 778 nm (pump) and lambda t = 84 2 nm (signal) with a sub-100-kHz linewidth. The high resolution spectromete r is being developed as an alternative to CO2 laser spectrometers in the 9- to 11-mu m range. Using a dual-arm cavity to enhance the two radiation pow ers, and with 35 mW in front of the 778-nm arm and 100 mW in front of the 8 42-nm arm, about 70 nW of the tunable 10-mu m radiation are generated. This power level is enough to investigate the linear absorption spectroscopy of SF6. Doppler-limited spectra over 2 GHz are recorded, showing the wide con tinuous tunability of the spectrometer.