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

Abstract

A trace ammonia (NH 3) 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 NH 3 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.

Fiber-Optic Photoacoustic Gas Sensor with Multiplexed Fabry–Pérot Interferometric Cantilevers

“…The maximum relative error is about −3.0%. By choosing a laser with appropriate wavelength, the sensor can also detect more types of gases, such as methane, ammonia, and hydrofluoric acid. − Due to the narrow line width characteristic of DFB lasers (about 2 MHz), gas absorption interference in general application environments is not large. However, for high-concentration interference backgrounds, the impact of laser absorption spectrum line overlap on the detection accuracy needs to be considered.…”

Optical Fiber Probe Microcantilever Sensor Based on Fabry–Perot Interferometer

“…Moreover, the high SNR and the high stability of the microphone make it suitable for resonance or non-resonance photoacoustic spectroscopy-based trace gas detection. The high sensitivity measurement of the trace acetylene, ammonia, and methane experiment has confirmed the ability of stainless-steel cantilever film with a 10 μm thickness to be an acoustic sensing component in all-optical photoacoustic spectroscopy [ 79 , 80 , 81 , 82 ]. The minimum detection limit of trace acetylene, ammonia, and methane are demonstrated to be 71 ppt, 3.2 ppb, and 15.9 ppb, respectively.…”

Cantilever-enhanced photoacoustic spectroscopy for gas sensing: A comparison of different displacement detection methods

“…Michelson interferometer has high sensitivity and good stability, but the bulky volume and high cost limit its application in some specific fields. CEPAS based on Fabry-Perot interferometer is relatively compact [50] , [51] , [52] , [53] , [54] , [55] , [56] , [57] , [58] , [59] , [60] , [61] , [62] . A Fabry-Perot cavity is formed between the end facet of the fiber and the free end of the cantilever.…”