Polymer-coated quartz tuning fork for enhancing the sensitivity of laser-induced thermoelastic spectroscopy

Abstract

A novel laser-induced thermoelastic spectroscopy (LITES) sensor based on a polymer-coated quartz tuning fork (QTF) is reported. Two types of polymer films with different thicknesses are deposited on commercially available QTF to improve the conversion efficiency of laser energy deposition into vibration. CO2 was selected as the target analyte for validation measurements. The experimental results indicate that by introducing a polymer coating, a maximum gain factor of 3.46 and 3.21 is attained for the signal amplitude and signal-to-noise ratio (SNR), respectively, when compared to traditional LITES that using only a bare QTF. A minimum detectable concentration of 0.181% can be obtained, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.74×10−11 cm−1·W·Hz−1/2, and the measurement precision is approximately 0.06% with an averaging time of 200 s. Here, we show what we believe is the first demonstration of polymer coated QTF for LITES sensing, compared with custom QTF, the design has the virtues of lower cost, simple and easy-to-operate, is a promising new strategy for sensitive trace gas analysis.

Ultra-highly sensitive HCl-LITES sensor based on a low-frequency quartz tuning fork and a fiber-coupled multi-pass cell

“…If the laser intensity is modulated, the QTF will suffer mechanical vibration at the modulation frequency and these vibrations are enhanced when the QTF operates in resonance conditions. LITES is a non-contact technique in which there is no need to place the QTF into the detected gases [32] , [33] , [34] , [35] . Therefore, this technique not only keeps the merits of QEPAS but also can be employed for detection of acid and corrosive gases.…”

Methane leakage monitoring system based on light-induced thermoelastic spectroscopy

“…In recent years, LITES gas detection technology has developed rapidly under the efforts of domestic and foreign researchers. It has been mainly studied from the aspects of theoretical simulation [11], structural improvement [12,13], signal demodulation [14] and signal enhancement [15][16][17], and achieved good results. To evaluate the accuracy of the methane leakage monitoring system, the minimum detection limit was evaluated.…”

Highly sensitive light-induced thermoelastic spectroscopy oxygen sensor with co-coupling photoelectric and thermoelastic effect of quartz tuning fork

“…The thermoelastic signal’s amplitude is proportional to the light absorption of the QTF, and the deposition of highly absorbing material on the QTF surface can improve the sensitivity [34] , [35] . In addition, to improve the photothermal conversion efficiency, polymeric materials with high thermal expansion coefficient were coated on QTF prongs [36] , [37] . But the surface coating method has its own shortcomings, such as too thick coating will reduce the quality factor (Q) and the detection sensitivity of the QTF sensor.…”