Quartz-enhanced photoacoustic spectroscopy sensing using trapezoidal- and round-head quartz tuning forks.

In this Letter, two novel, to the best of our knowledge, quartz tuning forks (QTFs) with trapezoidal-head and round-head were designed and adopted for quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing. Based on finite element analysis, a theoretical simulation model was established to optimize the design of QTF. For performance comparison, a reported T-head QTF and a commercial QTF were also investigated. The designed QTFs have decreased resonant frequency (f0) and increased gap between the two prongs of QTF. The experimentally determined f0 of the T-head QTF, trapezoidal-head QTF, and round-head QTF were 8690.69 Hz, 9471.67 Hz, and 9499.28 Hz, respectively. The corresponding quality (Q) factors were measured as 11,142, 11,411, and 11,874. Compared to the commercial QTF, the resonance frequencies of these QTFs have reduced by 73.45%, 71.07%, and 70.99% while maintaining a comparable Q factor to the commercially mature QTF. Methane (CH4) was chosen as the analyte to verify the QTFs' performance. Compared with the commercial QTF, the signal-to-noise ratio (SNR) of the CH4-QEPAS system based on the T-head QTF, trapezoidal-head QTF, and round-head QTF has been improved by 1.75 times, 2.96 times, and 3.26 times, respectively. The performance of the CH4-QEPAS sensor based on the QTF with the best performance of the round-head QTF was investigated in detail. The results indicated that the CH4-QEPAS sensor based on the round-head QTF exhibited an excellent linear concentration response. Furthermore, a minimum detection limit (MDL) of 0.87 ppm can be achieved when the system's average time was 1200 s.

Diode-pumped acousto-optical cavity-dumped Tm:YAP laser at 1989 nm.

In this paper, we demonstrated a diode-pumped acousto-optical cavity-dumped Tm:YAP laser for the first time. The pulses were coupled out of the lateral surface of the cavity when radio frequency signal was loaded on the acousto-optical modulator. A maximum output power of 1.28 W was obtained with pump power of 40.3 W at a repetition rate of 200 kHz, corresponding to a slope efficiency of 4.7%. The output pulse width of the cavity-dumped Tm:YAP laser was constant at 43 ns, and the wavelength was 1989.8 nm.

Cr:ZnS saturable absorber passively Q-switched Tm,Ho:GdVO4 laser.

A passively Q-switched Tm,Ho:GdVO4 laser operating at cryogenic temperature with a Cr(2+):ZnS saturable absorber pumped with continuous wave LDs was demonstrated. The performance of the laser was investigated through changing the distance between Cr(2+):ZnS and output coupler. The maximum pulse energy of 70.5 µJ was obtained at 10 W input power. The maximum average output power of PQS laser was up to 3.2 W at the pump power of 22.8 W, corresponding to CW output power of 7.4 W, pulse repetition frequency of 52 kHz, and a pulse width of 389 ns. The M(2) factor measured by the traveling knife-edge method was ~1.1 in x and y directions with near-diffraction limited beam quality.