Dual-comb photoacoustic and photothermal spectroscopy: A comprehensive review.

Dual-comb spectroscopy is one of the most powerful techniques for multispecies trace-gas sensing, attracting growing attention in both theoretical and experimental research. Firstly demonstrated and usually applied with direct absorption spectroscopy schemes, the dual-comb approach has been successfully combined with techniques like photoacoustic (PA) and photothermal (PT) spectroscopy in recent years. These techniques have been demonstrated to be particularly attractive because of their wavelength-independent and background-free detection, two key features allowing for the achievement of unprecedented dynamic range and flexibility. The integration of these techniques with dual-comb spectroscopy allows a significant enhancement in spectral resolution and bandwidth while preserving the peculiar features of PA and PT spectroscopy. Since the first proof-of-principle demonstration of dual-comb PA spectroscopy, several solutions based on acoustic transducers and optical cavities have been proposed to enhance the final sensitivity and optimize both detection bandwidth and spectral resolution. Starting from the description of the physical principles behind dual-comb PA and PT spectroscopy, this work presents a comprehensive review of the available state-of-the-art, focusing both on the different experimental setups and on a systematic comparison of the achieved results. Finally, the main challenges and prospects will be discussed, offering insights into potential directions for further innovation.