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-based, difference-frequency spectrometer using an AgGaS/sub 2/ nonlinear crystal. We use a type-II cut crystal as a part of the improvement compared with a type-I cut, which was used in our preliminary setup. The two tunable laser-diodes are operating near /spl lambda//sub 3/=778 nm (pump) and /spl lambda//sub 2/=842 nm (signal) with a sub-100-kHz linewidth. The high resolution spectrometer is being developed as an alternative to CO/sub 2/ laser spectrometers in the 9- to Il-/spl mu/m range. Using a dual-arm cavity to enhance the two radiation powers, and with 35 mW in front of the 778-nm arm and 100 mW in front of the 842 nm arm, about 70 nW of the tunable 10-/spl mu/m radiation are generated. This power level is enough to investigate the linear absorption spectroscopy of SF/sub 6/. Doppler-limited spectra over 2 GHz, are recorded, showing the wide continuous tunability of the spectrometer.