Performance characteristics of narrow linewidth fiber laser pumped mid-IR difference frequency mixing light source for methane detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of similar to2.3muW at 3.3mum with a slope efficiency of 0.85mW/W-2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm(-1) (3.2911 mum) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (similar to1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10m was also demonstrated.