Patent ID: 8594507

Claim:
A photoacoustic sensor comprising: a gas cell having an opening; a light source positioned outside the gas cell to generate radiation to radiate sample gas within the gas cell; a first membrane that is aligned with the opening of the gas cell to permit the sample gas to enter the gas cell; and an optical microphone to detect the sample gas within the gas cell and to generate output electrical voltage signals in response to acoustic signals generated by pressure fluctuations of the radiated sample gas caused by the radiation, the optical microphone including a semiconducting laser that has a p-n junction within a cavity, the optical microphone further including a second membrane different from said first membrane, said second membrane comprising a pressure-sensitive membrane that receives coherent light emitted from the semiconducting laser and directs reflected light back toward the cavity, the phase of the reflected light being dependent upon a distance of the pressure-sensitive membrane from the cavity; and wherein the second membrane of the optical microphone collects pressure fluctuations within the ambient environment when the light source that is positioned outside the gas cell is not producing radiation to determine spectral content of the pressure fluctuations within the ambient environment, and the photoacoustic sensor further comprises: a control that receives the output electrical voltage signals from the optical microphone that represent the spectral content of the pressure fluctuations within the ambient environment, the control selects a frequency of the radiation produced by the light source that is positioned outside the gas cell so that the spectral content of the pressure fluctuations produced within the gas cell when subjected to the radiation conflict less with the spectral content of the pressure fluctuations within the ambient environment.