Photoacoustic spectroscopy | EPFL Graph Search

Photoacoustic spectroscopy is the measurement of the effect of absorbed electromagnetic energy (particularly of light) on matter by means of acoustic detection. The discovery of the photoacoustic effect dates to 1880 when Alexander Graham Bell showed that thin discs emitted sound when exposed to a beam of sunlight that was rapidly interrupted with a rotating slotted disk. The absorbed energy from the light causes local heating, generating a thermal expansion which creates a pressure wave or sound. Later Bell showed that materials exposed to the non-visible portions of the solar spectrum (i.e., the infrared and the ultraviolet) can also produce sounds. A photoacoustic spectrum of a sample can be recorded by measuring the sound at different wavelengths of the light. This spectrum can be used to identify the absorbing components of the sample. The photoacoustic effect can be used to study solids, liquids and gases. Uses and techniques Photoacoustic spectroscopy has become a po

Gas traces measurement by photoacoustic spectroscopy using Helmholtz resonator-based sensors

Mario Mattiello

Photoacoustic spectroscopy is a well-established gas traces optical detection technique, which consists in the generation of an acoustic wave in the investigated gas compound excited by a modulated laser beam, and in the detection of this sound wave with a sensitive microphone. The sensitivity of this technique can be greatly enhanced through the use of acoustic resonators. A wide range of resonant configurations has been developed and reported in the literature in the last decades. Among these, Helmholtz resonators are known for their simplicity of implementation, though with a reduced efficiency. The main goal of this work is to demonstrate that Helmholtz resonators can be successfully applied to photoacoustic spectroscopy, delivering sensitivities in the same order of magnitude as other more common configurations, as well as offering a powerful tool to perform differential measurements. Two Helmholtz-based sensors are presented within this thesis. The first sensor has been developed for ammonia sensing, taking benefit from the properties of antimonide-based lasers; the final design has been the result of a carefully optimised compromise between high sensitivity, noise reduction, technical constraints, compact size and straightforward use. After several implemented improvements, an ultimate sub-ppm concentration detection limit has been achieved. The second sensor exploits the intrinsic phase shift existing between the two volumes of a Helmholtz resonator to perform differential measurements. Each of the two volumes of the resonator is filled with a different concentration of the same gas, whereas the exciting laser beam is split in two arms that separately illuminate the volumes, the resulting photoacoustic signal being proportional to the difference between the respective concentrations of the probed gas in the volumes. A particular detection scheme has been implemented to guarantee a linear measurement. The achieved sensitivity is not as high as obtained with the first sensor; nonetheless, the developed sensor offers the possibility to perform measurements that would otherwise require two different sensing devices, resulting in a clear gain in terms of cost and of detection complexity.

EPFL2008

Individually ventilated cages microclimate monitoring using photoacoustic spectroscopy

Jean-Philippe Besson, Marcel Gyger, Luc Thévenaz

A multi-gas photoacoustic sensor was developed In order to monitor microclimatic parameters at ppm level from the atmosphere of Individually ventilated cages housing mice. Ammonia, water vapour and carbon dioxide were measured on-line and in real-time during two weeks and 24 hours a day. The quality of bedding and the ventilation rate inside the cages has been monitored. The circadian activity level of these animals has then been observed.

VDI Verlag GMBH2004

Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

Jean-Philippe Besson, Luc Thévenaz

Multi-hydrogenated compounds detection based on photoacoustic (PA) spectroscopy is reported. Three near-infrared semiconductor lasers are used with a resonant PA cell operated in its first longitudinal mode to monitor methane, water vapour and hydrogen chloride in the parts per million range. The design of our cell results from simulations performed in order to optimise its performances. Influence of the buffer gas on the PA signal has also been analysed, both theoretically and experimentally. A reduction of the PA signal of almost one order of magnitude has been observed between N2 and He, which demonstrates the importance of the buffer gas in PA spectroscopy. Finally, detection limits of 0.5 ppm of CH4 and 3 ppm of HCl has been achieved experimentally in nitrogen and an H2O sensitivity of 0.2 ppm has been estimated. © 2004 Elsevier B.V. All rights reserved.

Elsevier2004

Gas traces measurement by photoacoustic spectroscopy using Helmholtz resonator-based sensors

Mario Mattiello

EPFL2008