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The analysis of geological samples using laser-induced breakdown spectroscopy (LIBS) is strongly affected by matrix effects. To investigate the improvement of matrix effects by the graphite doping method, rock powder was mixed with graphite powder and pressed into pellets. Four groups of samples with the same graphite content were prepared from a mixture of seven different rock powders and four graphite powders (0, 25, 50, and 75 wt.%). To reduce some of the pulse-to-pulse fluctuations, the internal standardization method was adopted. Four sets of calibration curves of Ca and Mg were prepared using pellet samples with the same graphite content. The influence of graphite content on laser-induced plasma temperature and electron density was further investigated. The coefficients of determination (R2) of the calibration curves after doping graphite are larger than those without doping, and the stability of the spectral intensity, plasma temperature, and electron density after doping are also improved. In particular, when the doping percentage is 50%, the matrix effect is significantly improved. The results show that the graphite doping method has great potential for improving the matrix effects of LIBS in the analysis of rock powder samples.

Based on tunable diode laser absorption spectroscopy (TDLAS), two-dimensional (2D) distribution reconstructions of gas concentration and temperature are realized using an algebraic reconstruction technique (ART). The influence of the beam distribution and grid size on combustion field reconstruction is investigated to attain optimal reconstruction results with a limited number of beams. Under limited optical-path numbers, it shows that a better spatial resolution is attainable only when the laser beam paths are vertical and parallel to the symmetry axis of the combustion field. Furthermore, experiments with 16 beam paths using one and two flat flame combustion fields are carried out in different fuel-air equivalence ratios under room temperature. The results are in agreement with the simulation results, and the time resolution is less than 1 s.

Photo-acoustic spectroscopy gas detection technology has the advantages of high sensitivity, good selectivity, small size and real time monitoring and has been widely used in environmental monitoring, industrial production, medical diagnosis, biological technology and monitoring of power facilities. In this paper, a method to improve the sensitivity of photo-acoustic spectroscopy system is presented, which is combined with the technique of Herriott type multiple pass cell. In this experimental apparatus, the design of the experimental device can make the beam pass the cell 18 times. By comparing the signal of one time pass through the photoacoustic cell and the signal of 18 times passes pass through the photoacoustic cell, we can confirm that the signal is increased and this method is feasible.

To monitor the velocity of industrial exhaust gas continuously,a parallel double-path flow velocity measurement system was designed,and the related theories on measuring the velocity of stack gas flow was studied based on the light scintillation.A simple phase-screen technique was used to analyze the light scintillation in a turbulent medium,and the expression of optical scintillation cross-correlation was obtained which is used to measure stack gas flow velocity.The path-weighting function of the mean velocity was given.The numerical simulation carried on path-weighting function indicates that it has axially symmetric distribution as Gaussian line shape,and the central velocity of the stack makes greater contribution.The impact of light source spectrum on path-weighting in principle was analyzed,and the preliminary experiments show that,although because the light source spectrum has a certain bandwidth,the path-weighting function has changed,the distribution is still axially symmetric.Based on the path-weighting function,the space distribution of the gas flow velocity in stack can be calculated.

Tunable diode laser absorption spectroscopy (TDLAS) has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv (parts-per-billion in volume), respectively.