Quartz-Enhanced Photoacoustic Detection of Gases in the Sub-Terahertz Range

Abstract

Developing sensitive and selective methods for detecting trace amounts of gases in the sub-terahertz (sub-THz) range is a pressing challenge for spectroscopy and environmental monitoring. Infrared and terahertz implementations of quartz-enhanced photoacoustic spectroscopy (QEPAS) have demonstrated high sensitivity through the use of quartz tuning forks (QTFs) as acoustic transducers. Key advantages of QTFs include their low cost, compact size, high quality factor, and wide spectral response, making the detector virtually wavelength-independent and allowing the use of a single element across widely separated frequency ranges. A promising approach is the development of hybrid configuration combining sub-THz sources based on frequency multiplier chains with focusing optics, which enhances the interaction of the radiation with the gaseous medium in the immediate vicinity of the resonator. In this study, an experimental setup was assembled that included a sub-THz signal generator with a frequency multiplier chain covering the 130–170 GHz range; a PTFE dielectric lens that focuses the beam onto a quartz tuning fork; the quartz resonator itself; and a lock-in amplifier with an ADC for signal collection. Focusing is essential at these wavelengths: the lens increases the power density delivered to the sensitive volume between the tuning fork prongs. A lock-in amplifier extracts a signal at the modulation frequency (or its harmonics) resulting from the photoacoustic effect generated in the gas upon absorption of subterahertz radiation. The developed setup is a prototype of a sensitive gas analyzer operating in the subterahertz range.
The work was performed according to the Government research assignment for TSU, project FSWM-2025-0038

Speaker

Nikolaev Viktor Vladimirovich
Tomsk State University
Russia

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