{"id":2039,"date":"2010-07-14T11:04:09","date_gmt":"2010-07-14T15:04:09","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=2039"},"modified":"2010-07-14T11:04:09","modified_gmt":"2010-07-14T15:04:09","slug":"microscale-photoacoustic-sensing","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/microscale-photoacoustic-sensing\/","title":{"rendered":"Microscale Photoacoustic Sensing"},"content":{"rendered":"

Photoacoustic spectroscopy [1<\/a>]<\/sup> is an optical absorption spectroscopy whereby the absorbed optical power is detected indirectly by sensing the thermal excitation and expansion of the sample using microphones or other mechanical displacement sensors.\u00a0 For trace-gas-sensing, specificity is achieved by tuning the optical excitation source to the narrow band absorption lines of the gas of interest.\u00a0 The accessibility of photoacoustic spectroscopy has improved due to the availability of inexpensive tunable diode-laser sources developed for telecommunications applications and continued innovation in semiconductor active materials [2<\/a>]<\/sup> [3<\/a>]<\/sup> is opening new spectral windows for detecting a wider variety of gasses.\u00a0 Photoacoustic detection of optical absorption has favorable scaling properties for miniaturization [4<\/a>]<\/sup> and miniature photoacoustic cells have been investigated [5<\/a>]<\/sup> along with compact resonant quartz tuning fork detectors [6<\/a>]<\/sup>.<\/p>\n

We are developing a photoacoustic spectroscopy system to perform distributed gas sensing using fiber optics and quartz tuning fork detectors.\u00a0 A schematic of the system is shown in Figure 1, where multiple photoacoustic detectors share one or more laser sources through a fiber optic switch.\u00a0 For each detector, the distal end of the optical fiber is aligned to terminate in between the tuning fork tines.\u00a0 Photoacoustic excitation of the tuning fork occurs when the target gas periodically absorbs energy from the wavelength modulated laser as the wavelength sweeps across the gas absorption line.\u00a0 Absorption spectra can be measured by tuning the center wavelength of the laser as shown in Figure 2.
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