Fiber-based quartz enhanced photoacoustic spectroscopy (QEPAS) is a method for trace gas sensing with excellent properties such as high sensitivity and strong applicability. It has received extensive attention and become particularly attractive in recent years. Therefore, this invited paper analyzed and summarized the principle of its sensing as well as its technical characteristics. The latest research results, combed with the application mechanism and application fields of different types of QEPAS system, were introduced. Finally, its development trend was forecasted.

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MgTiO 3 ceramic sample was synthesized and its Raman spectra were recorded. The Raman-active vibrational modes of MgTiO3 were calculated using first-principle calculations (density functional theory). Based on experimental data and calculation results, the Raman peaks were assigned as 225 cm−1 (Ag), 306 cm−1 (Ag), 398 cm−1 (Ag), 500 cm−1 (Ag), 715 cm−1 (Ag) and 281 cm−1 (Eg), 328 cm−1 (Eg), 353 cm−1 (Eg), 486 cm−1 (Eg), 641 cm−1 (Eg). The assignment was supported by the polarized Raman spectrum. Meanwhile, the symmetry coordinates of MgTiO3 primitive cell were analyzed and employed to expand the Raman-active modes.

In this paper, a hollow-core anti-resonant fiber (HC-ARF) based light-induced thermoelastic spectroscopy (LITES) sensor is reported. A custom-made silica-based HC-ARF with length of 75 cm was used as light medium and gas cell. Compared to a traditional multi-pass cell (MPC), the using of HC-ARF is advantageous for reducing the sensor size and easing the optical alignment. A quartz tuning fork (QTF) with a resonant frequency of 32766.20 Hz and quality factor of 12364.20 was adopted as the thermoelastic detector. Acetylene (C2H2) and carbon monoxide (CO) with absorption lines located at 6534.37 cm−1 (1530.37 nm) and 6380.30 cm−1 (1567.32 nm) were chosen as the target gas to verify such HC-ARF based LITES sensor performance. It was found that this HC-ARF based LITES sensor exhibits excellent linearity response to the analyte concentrations. The minimum detection limit (MDL) for C2H2 and CO detections were measured as 4.75 ppm and 1704 ppm, respectively. The MDL for such HC-ARF based LITES sensor can be further improved by using a HC-ARF with long length or choosing an absorption line with strong strength.