A photoacoustic spectroscopy sensor for nitrogen dioxide (NO 2 ) detection was presented based on a high-power broadband blue diode laser emitting at 446 nm. An optical chopper was replaced by a transistor transistor logic modulation signal generated by the signal generator to reduce mechanical noise. The detection limit of NO 2 sensor system reached to 46 ppt by the Allan variance analysis on the benefit of reflectionenhanced. A continuous detection of NO 2 in the atmosphere for 48 h was implemented in collaboration with an adaptive Kalman filter for lessening the noise in the measurement. The experimental results were highly consistent with the data of the China National Environmental Monitoring Center, demonstrating the accuracy and reliability of our NO 2 sensor system. This work provides a promising method for NO 2 and other atmospheric pollution gasses.

A palm-sized laser spectrometer has been developed for detecting trace gases based on tunable diode laser absorption spectroscopy (TDLAS) in combination with a novel double-layer toroidal cell. With the benefit of a home-made electronic system and compact optical design, the physical dimension of the sensor is minimized into 24×15×16 cm 3 . A toroidal absorption cell, with 84 reflections in 2 layers for an effective optical path length of 8.35 m, was used to enhance the absorption signals of gaseous species. A home-made electronic system was designed for implementing distributed feedback (DFB) diode laser controller, analog lock-in amplifier, data acquisition and communication. Calibration-free scanned wavelength modulation spectroscopy was employed to determine the concentration of the gas and reduce the random fluctuations from electronical noise and mechanical vibration. The measurement of CH4 in ambient air was demonstrated using a DFB laser at 1.653 μm. The rise time and fall time for renewing the gas mixture are approximately 16 s and 14 s, respectively. Vibration and temperature tests have been carried out for verifying the performance of the spectrometer, and standard deviations of 0.38 ppm and 0.11 ppm for 20 ppm CH4 at different vibration frequencies and temperatures, respectively, have been determined. According to the Allan deviation analysis, the minimum detection limit for CH4 can reach 22 ppb at an integration time of 57.8 s. Continuous measurement of atmospheric CH4 for two days validated the feasibility and robustness of our laser spectrometer, providing a promising laser spectral sensor for deploying in unmanned aerial vehicles or mobile robots.

We developed a type of toroidal multi-pass cell with multi-layer patterns based on the off-axis model when combined with absorption masks. The effective path-length of the original toroidal multi-pass cell is extended several roundtrips in comparison with the single-layer pattern, since the inner surface of the toroidal multi-pass cell is more efficiently utilized. The light pattern has been achieved by using the simple ring surface that is easy to fabricate. The exact analytical equations for the design of the toroidal multi-pass cell were derived based on analytical vector calculations. A series of numerical ray tracing simulations are presented, and the maximum theoretical optical path length that can be reached is 30 m with a setup of 5 cm column radius. Furthermore, two practical spot patterns are demonstrated with a path length of 8.3 m for 2-layer pattern and 10 m for 3-layer pattern with respective volumes of 71 mL and 110 mL.

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The temperature measurement of Sulfur dioxide (SO2) is a crucial parameter for accurately determining its concentration, particularly in high‐temperature environment. Herein, it is realized by using three different techniques, which are direct absorption spectroscopy, wavelength modulation spectroscopy and non‐calibration wavelength modulation spectroscopy based on the bispectral lines temperature measurement method. The bispectral lines of SO2 locates at 1396.844 and 1396.921 cm−1, respectively. The gas temperature in the absorption cell was also measured with K‐type thermocouple and compared with these three spectral measurements. The linearities corresponding to these three techniques are 99.71%, 99.8%, and 99.88%, respectively. Their average relative error between the spectral measurement results and the linear fitting value of the three techniques is 1.15%, 0.86%, and 0.57%, respectively. It is illustrated the feasibility of the bispectral lines method for high‐temperature measurement. These investigations provide methods for temperature measurement in high‐temperature coal‐fired boilers, potentially for investigating other sulfide gas molecules such as SO3 and H2S.

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Revealing the reaction mechanisms of the H−/D− + HD reaction – an exact quantum dynamics study on two potential energy surfaces.