Demonstration of a miniature all-optical photoacoustic spectrometer based on ferrule-top technology.

We present a miniaturized photoacoustic (PA) spectrometer obtained by carving a micromachined flexural pressure transducer directly at the top of a glass ferrule. The ferrule is equipped with two optical fibers, one for laser excitation of the gas and one for interferometric readout of the transducer. To demonstrate the working principle and assess the sensitivity of the device, we performed a set of measurements of C2H2 traces in an Ar buffer atmosphere. The data acquired show that our ferrule-top scheme allows one to increase the minimum detectable concentration by more than one order of magnitude with respect to the other miniaturized PA spectrometers reported in the literature, while decreasing the integration time by a factor of 10.