All-optical detection of acoustic pressure waves with applications in photoacoustic spectroscopy

Abstract

An all-optical detection method for the detection of acoustic pressure waves is demonstrated. The detection system is based on a stripped (bare) single-mode fiber. The fiber vibrates as a standard cantilever and the optical output from the fiber is imaged to a displacement-sensitive optical detector. The absence of a conventional microphone makes the demonstrated system less susceptible to the effects that a hazardous environment might have on the sensor. The sensor is also useful for measurements in high temperature (above 200• C) environments where conventional microphones will not operate. The proof-of-concept of the all-optical detection method is demonstrated by detecting sound waves generated by the photo-acoustic effect of NO2 excited by a 455 nm LED, where a detection sensitivity of approximately 50 ppm was achieved.

Direct Absorption and Photoacoustic Spectroscopy for Gas Sensing and Analysis: A Critical Review

“…Erbium‐doped ring lasers, [ 139 ] DFB, [ 140,141 ] $${\rm{C}}{{\rm{O}}_2}$$ lasers, [ 142 ] visible LEDs, [ 143 ] IR LEDs, [ 144 ] and THz diodes [ 145,146 ] are among the sources used with PA cells equipped with cantilevers. Lasers are more common than LEDs due to their higher optical power.…”

“…The detection of the PA signal was conducted using a bare single mode fiber SM acting as a cantilever. The output light from the fiber was imaged on a displacement detector [ 143 ] as shown in Figure a. It is easy to control the fiber's resonance frequency by adjusting its length before use since the resonance frequency is inversely proportional to the square of the fiber length.…”

“…The fiber was excited with a laser and the output light from the other side of the fiber was imaged on a displacement detector. [ 143 ] b) Cantilever with a rib waveguide on its top. By coupling light into the rib waveguide from one side and detecting the transmitted power from the other side, any deflection of the cantilever will affect the measured power, which is directly related to the deflection value.…”

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

“…Westergaard et al reported a CEPAS based on a stripped single-mode fiber [63] . The fiber itself was used as a cantilever and the emergent light of the fiber was detected by a split detector.…”

Quartz-Enhanced Photoacoustic Spectroscopy Assisted by Partial Least-Squares Regression for Multi-Gas Measurements

“…Of the many optical spectroscopic methods developed during the past century, photoacoustic spectroscopy (PAS) [ 17 , 18 , 19 , 20 , 21 ] has attracted considerable interest due to its powerful, yet simple, trace gas detection method and capability to detect multiple gasses with a single device. The PAS method is different from other optical absorption-based methods, where the absorbed energy translates into kinetic energy, which forms an acoustic wave that can be detected with a simple pressure transducer [ 17 , 22 , 23 ]. A variant of PAS is quartz-enhanced photoacoustic spectroscopy (QEPAS), which was introduced in 2002 [ 23 ] and is today an established spectroscopic technique [ 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”