Micro-Quartz Crystal Tuning Fork-Based Photodetector Array for Trace Gas Detection.

In this paper, a micro-quartz crystal tuning fork (M-QCTF) was first demonstrated for developing a low-cost, highly sensitive quartz tuning fork photodetector array for spectroscopic applications. A gas sensing system based on the M-QCTF photodetector and highly sensitive wavelength modulation spectroscopy was developed. Typically, an atmospheric greenhouse gas methane (CH) molecule was selected as the target analyte for evaluating the M-QCTF and standard commercial QCTF detectivity. The results indicate that the M-QCTF photodetector exhibits ∼3.3 times sensitivity enhancement compared to the standard commercial QCTF. The long-term stability was evaluated by using the Allan deviation analysis method; a minimum detection limit of 1.2 ppm was achieved with an optimal integration time of 85 s, and the corresponding normalized noise equivalent absorption coefficient was calculated to be 4.45 × 10 cm W/√Hz. Finally, a two-M-QCTF array detection scheme was experimentally demonstrated, and a signal-to-noise ratio enhancement factor of more than 1.7 times compared to that achieved using a single M-QCTF photodetector was realized, which proves a great potential for developing ultra-sensitive quartz tuning fork photodetector arrays for various applications.