No abstract

We have designed and built a wavelength-tunable optical source for standoff detection of gaseous chemicals by differential absorption spectrometry in the long-wave infrared. It is based on a nanosecond 2 µm single-frequency optical parametric oscillator, whose idler wave is amplified in large aperture Rb:PPKTP crystals. The signal and idler waves are mixed in Z n G e P 2 crystals to produce single-frequency tunable radiation in the 7.5–10.5 µm range. The source was integrated into a direct detection lidar to measure sarin and sulfur mustard inside a closed chamber, in an integrated path configuration with a noncooperative target.

We report on single-longitudinal-mode (SLM) operation of a low-threshold optical parametric oscillator, with a 17 nm tunability near 2 µm. The oscillator uses a MgO:PPLN crystal in Type 0 quasi-phase-matching configuration, pumped by a 1.064 µm SLM laser. Despite the huge acceptance bandwidth near-degeneracy of MgO:PPLN, spectral selection down to a SLM is achieved by combining a volume Bragg reflector and Vernier filtering in nested signal and idler cavities. Tunability over 17 nm is demonstrated owing to a transverse chirp of the grating period of the Bragg reflector.