Tunable fiber laser and fiber amplifier based photoacoustic spectrometer for trace gas detection.

A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and an erbium doped fiber amplifier (EDFA) is first developed for trace gas detection. This sensor has been applied to the detection of ammonia using a first longitudinal resonant photoacoustic cell with double absorption optical path (L=20cm) and lock-in harmonic detection technique. The minimum detectable limit of 3 parts-per-billion volume (signal-to-noise ratio=1) and response time of approximately 1min is achieved at room temperature and atmospheric pressure with 100ms time constant and 500mW optical power at the 1531.7nm transition line.