Portable fiber-coupled diode-laser-based sensor for multiple trace gas detection

Tunable narrowband mid-infrared radiation from 3.25 to 4.4 mu m is generated by a compact fiber-coupled, difference-frequency-based spectrosopic source. A 20-mW external cavity-diode laser (with a tuning range from 814 to 870 nm) and a 50-mW distributed-Bragg-reflector diode-laser-seeded ytterbium-doped fiber amplifier operating at 1083 nm are difference-frequency mixed in a multi-grating, temperature-controlled periodically poled LiNbO3 crystal. A conversion efficiency of 0.44 mW/(W(2)cm) (corresponding to a power of approximate to 3 mu W at 3.3 mu m) represents the highest conversion efficiency reported for a portable device. Performance characteristics of such a sensor and its application to spectroscopic detection of CO2, N2O, H2CO, HCl, NO2, and CH4 will be reported in this work.