Quartz crystal tuning fork based 2f/1f wavelength modulation spectroscopy

Abstract A compact gas sensing system based on the quartz crystal tuning fork (QCTF) and 2f/1f wavelength modulation spectroscopy (2f/1f-WMS) technique was reported for the first time. An ingenious laser modulation strategy and frequency division multiplexing demodulation algorithm were developed for realizing a single QCTF to detect the first harmonic and second harmonic signals simultaneously. The influence of laser power change and excitation position the QCTF based 2f/1f-WMS technique was first investigated in detail. The results show that, compared with the traditional QCTF-2f method, the reported QCTF based 2f/1f technique has better immunity. To further evaluate this sensing technique, real-time monitoring of ambient water vapor (H2O) was made, the results show that the developed QCTF based 2f/1f-WMS technique can effectively improve the long-term stability and has super anti-interference ability to various environmental disturbance factors, such as light beam jitter, airflow fluctuation, and mechanical vibration, which proves it has great potential in practical field applications, especially for harsh environment.