Trace Ammonia Detection Based on Near-Infrared Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy

摘要

A trace ammonia(NH3)detection system based on the near-infrared fiber-optic cantilever-enhanced photoacoustic spectroscopy(CEPAS)is proposed.A fiber-optic extrinsic Fabry-Perot interferometer(EFPI)based cantilever microphone has been designed to detect the photoacoustic pressure signal.The microphone has many advantages,such as small size and high sensitivity.A near-infrared tunable erbium-doped fiber laser(EDFL)amplified by an erbium-doped fiber amplifier(EDFA)is used as a photoacoustic excitation light source.To improve the sensitivity,the photoacoustic signal is enhanced by a photoacoustic cell with a resonant frequency of 1624 Hz.When the wavelength modulation spectroscopy(WMS)technique is applied,the weak photoacoustic signal is detected by the second-harmonic detection technique.Trace NH3 measurement experiments demonstrate that the designed fiber-optic CEPAS system has a linear response to concentrations in the range of 0 ppm‒20 ppm at the wavelength of 1522.448 nm.Moreover,the detection limit is estimated to be 3.2 ppb for a lock-in integration time of 30 s.