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

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 photoacoustic effect of NO2 excited by a 455 nm LED, where a detection sensitivity of approximately 50 ppm was achieved.