Abstract
A highly sensitive Fabry–Perot based transduction method is proposed as an all-optical alternative for the detection of trace gas by the photoacoustic spectroscopy technique. A lumped element model is firstly devised to help design the whole system and is successfully compared to finite element method simulations. The fabricated Fabry–Perot microphone consists in a hinged cantilever based diaphragm, processed by laser cutting, and directly assembled at the tip of an optical fiber. We find a high acoustic sensitivity of 630 mV/Pa and a state-of-the-art noise equivalent pressure, as low as at resonance. For photoacoustic trace gas detection, the Fabry–Perot microphone is further embedded in a cylindrical multipass cell and shows an ultimate detection limit of 15 ppb of NO in nitrogen. The proposed optical trace gas sensor offers the advantages of high sensitivity and easy assembling, as well as the possibility of remote detection.
Highlights
The photoacoustic (PA) effect consists in the generation of an acoustic wave originating from the specific absorption of laser radiation by the medium of interest
For photoacoustic trace gas detection, the Fabry–Perot microphone is further embedded in a cylindrical multipass cell and shows an ultimate detection limit of 15 ppb of NO in nitrogen
The proposed optical trace gas sensor offers the advantages of high sensitivity and easy assembling, as well as the possibility of remote detection
Summary
The photoacoustic (PA) effect consists in the generation of an acoustic wave originating from the specific absorption of laser radiation by the medium of interest. Based on this phenomenon, the photoacoustic spectroscopy technique enables high sensitivity probing [1,2] and sensing [3,4]. The modulation of the optical power or wavelength creates a variation of the heat produced, acting as a harmonic source for the photoacoustic pressure wave, whose amplitude indicates the targeted molecules concentration. A generic trace gas photoacoustic sensor can be composed of a laser, a closed volume, called the cell, where the acoustic wave is generated, and a transducer for the detection of the pressure variation The mid-infrared range, often called the molecule fingerprint region, is a very interesting zone for photoacoustic spectroscopy, where most molecules of interest (polluting or toxic gases, biomarkers, etc.) have a specific spectral signature.
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