Photoacoustic spectroscopy and light-induced thermoelastic spectroscopy based on inverted-triangular lithium niobate tuning fork

In this paper, a novel self-designed inverted-triangular lithium niobate tuning fork (LiNTF) was used to construct gas sensing system for the first time. The optimal ratio of the upper and lower boundaries of the inverted-triangular LiNTF is found by scanning through finite element analysis (FEA). The surface charge density and stress value of the inverted-triangular LiNTF are both higher than those of the standard quartz tuning fork (QTF). In the lithium niobate-enhanced photoacoustic spectroscopy (LiNPAS) sensing system, the 2f peak and signal-to-noise ratio (SNR) of the inverted-triangular LiNTF are 7.41 times and 5.89 times those of the standard QTF, respectively. After forming acoustic standing wave field with the acoustic micro-resonator (AmR), the LiNPAS system achieves an SNR 56.16 times higher than without the AmR. Based on Allan variance analysis, the system achieves a minimum detection limit (MDL) of 7.25 ppb with an averaging time of 800 seconds. In the light-induced thermoelastic spectroscopy (LITES) sensing system, the 2f peak and SNR of the inverted-triangular LiNTF are 7.82 times and 6.03 times those of the standard QTF, respectively. When the averaging time reaches 100 s, the MDL of the system is found to be 25.78 ppb.