CH_4 monitoring in ambient air by communication band laser diode based difference frequency generation in a quasi-phase-matched LiNbO_3 waveguide

摘要

Methane in ambient air is detected by difference frequency generation in a direct-bonded quasi-phase-matched LiNbO_3 ridge waveguide using near infrared communication band laser diodes as pump and signal sources. Absorption lines for the Q branch in the 3.3 μm v_3 band are measured by using a Hanst configuration multipass cell with a 107 m path length. The authors detect 35 ppb CH_4 in 2 kPa ambient air with a single wavelength scan of a signal external cavity laser diode by suppressing various spectroscopic fringes and stabilizing the pump laser diode oscillation mode with a fiber Bragg grating.