Improvement of laser induced breakdown spectroscopy signal using gas mixture

Abstract

Laser induced breakdown spectroscopy (LIBS) is a spectral analysis technique characterized by the merits including rapidity, simple sample preparation, and spontaneous multi-element analysis, etc. In LIBS detection, the ambient gas plays an important role in interacting with the fast-expanding laser induced plasma (LIP) and greatly affects the LIBS signal. Therefore, it is important to investigate the effects of the ambient gas, especially the gas properties such as molecular weight, ionization energy, and thermal capacity, etc. on LIBS signals to better understand the interactions between the surrounding gas and the LIP, and improve the signal quality of LIBS. However, it is very hard to change only one property of the ambient gas while keeping the others unchanged because of the unavailability of such gases, thus in this study, a series of gas mixtures composed of He, Ne and Ar were utilized to obtain diverse properties necessary for the investigation, while titanium alloy is used as a sample. Results revealed that for some gas mixtures (such as 40% He, 40% Ne, and 20% Ar gas mixture), signal intensities were enhanced and relative standard deviation (RSD) values were significantly decreased. The plasma temperature T, electron density ne, and total number density ns were also calculated to analyze the mechanism of gas effect on LIBS signals. Results showed that the change of the gas species mainly has influences on the total number density ns, and further leads to the change of signals intensities and RSDs. The relation between some gas properties and LIBS signal was then discussed and the mechanism of some leading properties, such as the molecular weight, ionization energy, thermal conductivity, and viscosity were analyzed to explain how these properties work on LIBS signals.