Nowadays, both the scientific effort and the technological progress have been pushing the development of more compact and high-performing trace-gas sensors for a variety of daily life applications. Starting with environmental monitoring, including air, water and soil quality control, their high versatility allows them to be applied in sectors such as breath analysis for non-invasive disease diagnosis like diabetes, renal failure, asthma, and hypercholesterolemia.
A particular type of sensor is represented by Photo-Acoustic sensors (PAS), whose physical principle lays its basis on the non-radiative de-excitation of a selected molecule following its interaction with a modulated (in amplitude or in frequency) laser beam and the generation of sound waves in the gas sample. The PASs can provide several unique advantages if compared to direct absorption techniques. First, thanks to the indirect detection schemes, in a PAS setup, no photodetectors are needed to measure the photo-acoustic signal, thus allowing a highly flexible selection of the working wavelength (and so of the selected trace molecule). Furthermore, it is worth mentioning the absence of background in the absence of a photo-acoustic signal and the high versatility and scalability of the entire setup, which make PASs particularly suitable for far- and in-field applications.
During the last two decades, scientific effort has been focused on the development of photo-acoustic-based techniques able to guarantee increasingly lower trace-gas detection sensitivities. Among them, the most commonly used are Quartz-Enhanced PAS (QEPAS) [1] and Cantilever-Enhanced PAS (CEPAS) [2], whose combinations with innovative architectures for great sound wave amplification [3] and with high-finesse optical cavities for optimal radiant power enhancement [4,5] have been crucial for reaching world-record performances.
In this framework, our research group is engaging with the realization of photo-acoustic based sensors able to achieve detection sensitivities down to the part-per-trillion (ppt) or even below. Starting from the fabrication and characterization of novel silicon-based Micro-Electro-Mechanical Systems (MEMSs) as acoustic-to-voltage transducers [6], the development of an all-optical sensitive interferometric readout [7], the exploitation of high-finesse optical for great signal enhancement [8], and the characterization of shot-noise limited mid-IR radiation for photo-acoustic effect generation [9], our goal is to simultaneously optimize all the key parts of the entire system.
[1] Anatoliy A Kosterev, et asl. “Quartz-enhanced photoacoustic spectroscopy”. Optics letters, 27(21):1902–1904, 2002.
[2] Koskinen, V., et al. ”Progress in cantilever enhanced photoacoustic spectroscopy.” Vibrational spectroscopy 48.1 (2008): 16-21.
[3] Dello Russo, Stefano, et al. “Acoustic coupling between resonator tubes in quartz-enhanced photoacoustic spectrophones employing a large prong spacing tuning fork.” Sensors 19.19 (2019): 4109.
[4] Borri, S., et al. “Intracavity quartz-enhanced photoacoustic sensor.” Applied Physics Letters 104.9 (2014).
[5] Wang, Zhen, et al. “Doubly resonant sub-ppt photoacoustic gas detection with eight decades dynamic range.” Photoacoustics 27 (2022): 100387.
[6] Pelini, Jacopo, et al. “New silicon-based micro-electro-mechanical systems for photo-acoustic trace-gas detection.” Photoacoustics (2024): 100619.
[7] M. Siciliani De Cumis, Simone Borri, Mariaconcetta Canino, Pablo Cancio Pastor, Paolo De Natale, Inaki Lopez Garcia, Alberto Roncaglia, Patent No. WO2023126455A1(2023). https://patents.google.com/patent/WO2023126455A1/
[8] Pelini, Jacopo, et al. “High-performance cavity-enhanced photoacoustic trace-gas sensing.” Quantum Sensing and Nano Electronics and Photonics XX. Vol. 12895. SPIE, 2024.
[9] Marschick, Georg, et al. “Mid-infrared Ring Interband Cascade Laser: Operation at the Standard Quantum Limit.” ACS photonics (2024).
