Demonstration of a highly sensitive photoacoustic spectrometer based on a miniaturized all-optical detecting sensor

We report on the development of a highly sensitive photoacoustic (PA) spectrometer based on a miniaturized all-optical detecting sensor. The sensor has a cell volume of less than 6 μL and relies on a cantilever-based acoustic transducer, which is equipped with an optical fiber interferometric readout. The spectrometer reaches a noise equivalent concentration of 15 ppb (300 ms time constant) for acetylene detection using a 23 mW excitation laser source, which corresponds to a normalized noise equivalent absorption coefficient of 7.7 × 10^-10 W cm^-1 Hz^-1/2. The performance offered by this PA spectrometer is thus comparable to those reported for bulkier PA analyzers. Furthermore, because both the excitation and detection signals are brought to the PA cell via optical fibers, our spectrometer can be used in harsh environments, where electronic devices are prone to failure, and it is specially suitable for multiplexed remote detection applications. We believe that our study paves the way for the development of PA spectrometers that allow in-situ gas detection in space-limited circumstances.