Development of a Doppler-broadened NICE-OHMS system for trace gas detection based on a single sideband phase modulator

To expand the applicability of noise-immune cavity-enhanced optical heterodyne molecular spectrometer (NICE-OHMS), a universal system incorporating fiber-coupled single-sideband modulator (f-SSM) for control laser frequency has been developed. A homemade PID servo mainly composed two integrators designed, resulting in locking bandwidth 170 kHz and continuous tuning range 2.2 GHz. The exhibits noise-equivalent Doppler-broadened absorption limit 8.0×10 −14 cm −1 an integration time 64 s. Since f-SSM is sole external actuator, this opens up NICE-OHMS based on multitude systems.