Ma Weiguang

Theoretical analysis of cavity saturation spectroscopy of weak molecular absorbance

A theoretical analysis of sub-Doppler molecular saturation spectroscopy by use of a confocal Fabry–Perot (CFP) cavity is presented. The effects of gas pressure, cavity length and mirror reflectivity on the saturation dip amplitude are analysed. Such a treatment can provide the optimum conditions and a guidance for the experiment of saturating the weak molecular absorption lines.

Quantitative CF-LIBS analysis of alloys via comprehensive calibration of plasma temperature and spectral intensity

The chemical composition of alloys directly determines their mechanical behaviors and application fields. Accurate and rapid analysis of each element in alloys plays a key role in metallurgy quality control and material classification processes. A quantitative calibration-free laser-induced breakdown spectroscopy (CF-LIBS) analysis method, which carries out comprehensive calibration of plasma temperature and spectral intensity by using a second-order iterative algorithm and a similar matrix standard sample, is proposed to compare the standard errors that correspond to various plasma temperatures and calibration coefficients. Once the minimal standard error is found, we can optimize both the plasma temperature and the calibration coefficient of the minor element emission line, and establish the quantitative analysis model to realize accurate elemental composition measurements. In our experiments, the ZBY910 copper-lead alloy is selected to be the standard sample. Here, 6 Cu I lines and 5 Pb I lines are utilized to draw the Boltzmann plots, and the plasma temperature is predicted to be in the range of 5000–10000 K. Experimental results show that, the optimal plasma temperature and correction coefficient are found to be 7710 K and 0.61, respectively, as the standard error reaches its minimum of 0.06. Compared to conventional CF-LIBS analysis, the relative errors for major elements Cu and Zn and minor element Pb in the samples have been reduced from 13%, 20%, and 74% to 4.4%, 6.2%, and 17.7%, respectively, which are much superior to those of the conventional CF-LIBS method. This new method has greatly improved the quantitative analysis accuracy of CF-LIBS and realized more accurate measurement of both major and minor elements in alloy samples. It is expected to promote the application of CF-LIBS technology in fields such as metallurgical quality monitoring, material identification, classification, etc.

Investigation and performance evaluation of optically thin laser-induced breakdown spectroscopy without self-absorption

In order to avoid the self-absorption effects presented in the laser-induced breakdown spectroscopy (LIBS) for industrial application, a novel optically thin LIBS (OT-LIBS) technique has been developed, investigated and evaluated. By comparing the elemental doublet lines intensity ratios with the theoretical one, we can reset the delay time of exposure of the intensified CCD (ICCD) and obtain the non-self-absorption emission line directly. In this experiment, once the delay time is set to 500 ns, the traditional LIBS experimental setup has been converted to the OT-LIBS one. The experimental parameters that corresponded to OT-LIBS were optimized, and the optically thin condition of the induced plasma was validated. The linear correlation coefficients of the Boltzmann plot is larger than 0.99, as well as the SA coefficient reaches its maximum, which verify that the plasmas generated by OT-LIBS are indeed in optically thin condition. Univariate quantitative analysis results performed on several self-made pallets show that, compared to the traditional LIBS, OT-LIBS has improved the linear correlation coefficient R 2 of calibration line for aluminium from 0.86 to 0.98, and reduced the mean absolute measurement error from 1.2% to 0.13%. The measurement accuracy has been improved by nearly an order of magnitude, but the measurement repeatability has not been improved. In addition, also the boundary conditions, applicability and limitation of OT-LIBS are also investigated. It is certified that the limitations of concentration and pulsed laser energy are 0–20.8% and larger than 16.9 mJ, while the applicable concentration and pulsed laser energy are 0–15.9% and larger than 33.1 mJ. This OT-LIBS technique is expected to promote the practical processes of LIBS in industrial application.

The Hansch-Couillaud frequency locking mechanism of dual-wavelength external cavity resonance system based on diffusion bonded KTP crystal

Dual-wavelength external cavity resonance is achieved by Hansch-Couillaud(HC) frequency locking technology based on diffusion bonded KTP crystal. The HC frequency locking scheme based on diffusion bonded KTP crystal is analyzed theoretically and experimentally. The results show that the laser frequency can be locked to the resonance peak of e 1 -light or e 2 -light, compared with the results of a single KTP crystal. The longitude mode frequency of bow-tie cavity is locked at the frequency of 938nm laser firstly, and then the longitude mode frequency of bow-tie cavity is locked at the frequency of 1583 nm laser. The phase correlated locking of three components is realized.