Distributed-feedback-laser-based NICE-OHMS
in the pressure-broadened regime

Abstract

A compact noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) system based on a narrow linewidth distributed-feedback laser and fiber-coupled acousto-optic and electro-optic modulators has been developed. Measurements of absorption and dispersion signals have been performed at pressures up to 1/3 atmosphere on weak acetylene transitions at 1551 nm. Multiline fitting routines were implemented to obtain transition parameters, i.e., center frequencies, linestrengths, and pressure broadening coefficients. The signal strength was shown to be linear with pressure and concentration, and independent of detection phase. The minimum detectable on-resonance absorption with a cavity with a finesse of 460 was 2 × 10(-10) cm(-1) for 1 minute of integration time.