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Journal Article

Dual-frequency modulation quartz crystal tuning fork-enhanced laser spectroscopy


Fischer,  Horst
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Xu, L., Liu, N., Zhou, S., Zhang, L., Yu, B., Fischer, H., et al. (2020). Dual-frequency modulation quartz crystal tuning fork-enhanced laser spectroscopy. Optics Express, 28(4), 5648-5657. doi:10.1364/OE.386205.

Cite as: http://hdl.handle.net/21.11116/0000-0007-4B62-7
An innovative trace gas-sensing technique utilizing a single quartz crystal tuning fork (QCTF) based on a photoelectric detector and dual-frequency modulation technique was demonstrated for the first time for simultaneous multi-species detection. Instead of traditional semiconductor detectors and lock-in amplifier, we utilized the piezoelectric effect and resonant effect of the QCTF to measure the light intensity. A fast signal analysis method based on fast Fourier transform (FFT) algorithm is proposed for overlapping signal extraction. To explore the capabilities of this technique, a gas-sensing system based on two lasers having center emission wavelength of 1.653 µm (a DFB laser diode in the near-IR) and 7.66 µm (an EC QCL in the mid-IR) is successfully demonstrated for simultaneous CH4 spectroscopy measurements. The results indicate a normalized noise equivalent absorption (NNEA) coefficients of 1.33×10−9 cm−1W·Hz−1/2 at 1.653 µm and 2.20×10−10 cm−1W·Hz−1/2 at 7.66 µm, were achieved. This proposed sensor architecture has the advantages of easier optical alignment, lower cost, and a compactness compared to the design of a conventional TDLAS sensor using multiple semiconductor detectors for laser signal collection. The proposed technique can also be expanded to common QEPAS technique with multi-frequency modulation for multiple species detection simultaneously.