In situ rapid classification of rock lithology is crucial in various fields, including geological exploration and petroleum logging. Laser-induced breakdown spectroscopy (LIBS) is particularly well-suited for in situ online analysis due to its rapid response time and minimal sample preparation requirements. To facilitate in situ raw rock discrimination analysis, a portable LIBS device was developed specifically for outdoor use. This device built upon a previous multi-directional optimization scheme and integrated machine learning to classify seven types of original rock samples: mudstone, basalt, dolomite, sandstone, conglomerate, gypsolyte, and shale from oil logging sites. Initially, spectral data were collected from random areas of each rock sample, and a series of pre-processing steps and data dimensionality reduction were performed to enhance the accuracy and efficiency of the LIBS device. Subsequently, four classification algorithms—linear discriminant analysis (LDA), K-nearest neighbor (KNN), support vector machine (SVM), and extreme gradient boosting (XGBoost)—were employed for classification discrimination. The results were evaluated using a confusion matrix. The final average classification accuracies achieved were 95.71%, 93.57%, 92.14%, and 98.57%, respectively. This work not only demonstrates the effectiveness of the portable LIBS device in classifying various original rock types, but it also highlights the potential of the XGBoost algorithm in improving LIBS analytical performance in field scenarios and geological applications, such as oil logging sites.

The development of a fast in situ optical sensor based on a continuous-wave (cw) quantum cascade laser (QCL) operating at 8 μm for measurement of environmental gaseous nitrous acid (HONO) is reported. A strong absorption line at 1252.2109 cm $^{-1}$ is found to be free of interferences and used for the first time for ambient HONO detection. Loss of HONO on the wall of the gas sample absorption cell is evaluated. The resulting 1-s detection limit for HONO is 110 pptv with a folded path length of 172 m. Continuous monitoring of HONO and NO2 mixing ratios variations along with the basic meteorological parameters were performed during a field campaign of several days. Typical photochemical reactions of HONO have been observed on sunny and snowy days. Atmospheric HONO mixing ratios observed in this study indicate that direct emission from traffic exhausts and local heterogeneous reactions are potentially important sources of HONO.

In order to achieve the accurate measurement of gas stable isotope, according to the structure of gas cavity and the characteristics of optical elements, a constant temperature and pressure gas isotope measurement experimental system based on tunable diode laser absorption spectroscopy (TDLAS) technology is designed, which can achieve high-precision and stable control of temperature and pressure in the box. The hardware circuit system including high-precision constant-current source, two-channel temperature sampling module, conditioning circuit and pressure control circuit is designed in the system. The corresponding system closed-loop control software is developed to ensure the stability of the temperature and pressure of the optical cavity. Through the experimental verification, the temperature is controlled at 35ºC and the pressure is controlled at 150 mbar in the present work. The measurement results verified the stability of the temperature and pressure system, as follows: the optimal temperature fluctuation control is ±0.005ºC and the pressure stability is ±0.1 mbar. Then, in our experiment, the CH4 standard gas is introduced to measure carbon isotope (12CH4 and 13CH4). The results clearly show that the control system is sufficiently stable to be used and the δ13C value can reach 0.52‰ according to the Allan variance.

In this study, a method for double-beam quantum cascade laser absorption spectroscopy (DB-QCLAS) was developed. Two mid-infrared distributed feedback quantum cascade laser beams were coupled in an optical cavity for the monitoring of NO and NO₂ (NO at 5.26 μm; NO₂ at 6.13 μm). Appropriate lines in the absorption spectra were selected, and the influence of common gases in the atmosphere, such as H₂O and CO₂, was avoided. By analyzing the spectral lines under different pressure conditions, the appropriate measurement pressure of 111 mbar was selected. Under this pressure, the interference between adjacent spectral lines could be effectively distinguished. The experimental results show that the standard deviations for NO and NO₂ were 1.57 ppm and 2.67 ppm, respectively. Moreover, in order to improve the feasibility of this technology for detecting chemical reactions between NO and O₂, the standard gases of NO and O₂ were used to fill the cavity. A chemical reaction instantaneously began, and the concentrations of the two gases were immediately changed. Through this experiment, we hope to develop new ideas for the accurate and rapid analysis of the process of NOx conversion and to lay a foundation for a deeper understanding of the chemical changes in atmospheric environments.

At present, gas monitoring technology based on optical principle has been widely used in atmospheric environment, industrial emissions, smart city and other monitoring fields. For the requirement of high precision and high stability control of temperature and pressure of laser absorption spectroscopy measuring instrument, the temperature and pressure control scheme of the system is studied. The temperature and pressure control system is identified and the simulation model is established. The consistency of temperature and pressure models is 99.35% and 95.55% by using Process Models module to debug continuously. The simulation compares the output response curves of different control methods with the same step signal input, and the Fuzzy Adaptive PID parameter control algorithm achieves the design requirements in response time, overshoot and other aspects.

Due to the fact of global warming, air quality deterioration and health concern over the past few decades, great demands and tremendous efforts for new technology to detect hazard gases such as CH4, CO2, CO, H2S, and HONO have been performed. Tunable diode laser absorption spectroscopy (TDLAS) is a kind of technology with advantages of high sensitivity, high selectivity, and fast responsivity. It has been widely used in the applications of greenhouse gas measurements, industrial process control, combustion gas measurements, medicine, and so on. In this chapter, we will briefly summarize the most recent progress on TDLAS technology and present several kinds of gas sensors developed mainly by our group for various field applications. These could expand from energy, environment, and public safety to medical science.