Optical cavities are essential for enhancing the sensitivity of molecular absorption spectroscopy, which finds widespread high-sensitivity gas sensing applications. However, the use of high-finesse cavities confines the wavelength range of operation and prevents broader applications. Here, we take a different approach to ultrasensitive molecular spectroscopy, namely dual-comb optomechanical spectroscopy (DCOS), by integrating the high-resolution multiplexing capabilities of dual-comb spectroscopy with cavity optomechanics through photoacoustic coupling. By exciting the molecules photoacoustically with dual-frequency combs and sensing the molecular-vibration-induced ultrasound waves with a cavity-coupled mechanical resonator, we obtain high-resolution broadband (>2 THz) overtone spectra for acetylene gas. The detection limit down to 15 parts per trillion is achieved without the restriction on the comb wavelengths. Our innovative approach not only enriches the practical applications of the emerging cavity optomechanics technology but also offers intriguing possibilities for multi-species trace gas detection.
The study of non-linear interactions in semiconductor photo-electronic devices to achieve effective and fast photon identification is an ongoing and important task. We investigated the specific contribution of degenerate and non-degenerate two-photon absorption (D-TPA and ND-TPA) response in silicon avalanche photodiode (Si-APD) for infrared photon detection at room temperature. We experimentally demonstrated that when the two laser pulses overlapped, the average D-TPA quantum detection efficiencies at 1800 nm, and that at 1550 nm were measured as 3.3×10 -16 counts•pulse/photon 2 , 4.3×10 -15 counts•pulse/photon 2 , respectively. And the ND-TPA quantum detection efficiency of 1800 nm and 1550 nm was measured to be 7.9×10 -16 counts•pulse/photon 2 . This study provides a solution for the practical infrared photon detection devices based on TPA effect in Si-APDs.
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