Membraneless optical microphone based photoacoustic spectroscopy for trace gas detection

We present an advanced membraneless optical microphone (MeoM)-based photoacoustic spectroscopy (PAS) system for trace gas detection. The MeoM-PAS combines Michelson interferometry with photoacoustic resonance to achieve all-optical detection by sensing minute refractive index variations between the two interferometer arms induced by photoacoustic pressure fluctuations. The all-optical design enhances stability and reduces both acoustic and electromagnetic interference. This configuration also allows the optical components to remain physically isolated from the target gas, enabling non-contact measurement. A resonant gas cell was designed to match the interferometric configuration, and an experimental platform was established to evaluate the MeoM-PAS performance with NO₂. Experimental results showed that the system achieved a minimum detection limit of 4.1 ppb, further improved to 2.5 ppb at an averaging time of 107 s, as determined by Allan deviation analysis. These results demonstrate the feasibility of the MeoM-PAS approach for trace gas monitoring in atmospheric and industrial applications.