Remote sensing of methane gas by differential absorption measurement using a wavelength tunable DFB LD

In the method described a single wavelength tunable distributed-feedback laser diode (DFB LD) in the 1.65- mu m region is used to emit two different wavelengths of equal power which are modulated 180 degrees out of phase with each other at a frequency of 10 kHz. One of the two wavelengths is frequency stabilized via a methane gas cell and a feedback system equipped with a lock-in amplifier. A sensitivity of 4 p.p.m.-m methane in 1-atm nitrogen has been achieved. This light source has greatly simplified the setup for the measurements of this kind.<
>