Back-reflection-enhanced laser-induced breakdown spectroscopy (BRELIBS) on transparent materials: Application on archaeological glass.

A straightforward and simple method has been proposed in the current work to improve the signal-to-noise ratio of the LIBS spectrum of transparent samples. The idea is to benefit from a highly polished metallic reflector in direct contact with the rear surface of the transparent target. Copper and silver metals have been used as reflectors for the focused laser beam and force it to pass through the plasma plume induced initially onto the front surface of the target. The reflected laser beam reheats the plasma plume increasing the intensity of the light emitted from it. In such a case, the obtained LIBS spectrum accomplishes a pronounced increase in the signal-to-noise ratio compared to the spectrum obtained without a reflector. The new amendment of the LIBS technique setup has been exploited for the elemental analysis of colored glass fragments from archaeological Egyptian Synagogue windows. Quantitative analysis of the samples using the calibration-free LIBS (CF-LIBS) approach has been performed. The results depicted three-to four-fold enhancement in the spectral lines' intensity depending on the glass color and thickness. The results have been validated by the quantitative analysis of the same samples via the Energy-Dispersive X-ray spectroscopy (EDX). The CF-BRELIBS results were in pronounced agreement with that of the EDX. The back-reflection-enhanced laser-induced breakdown spectroscopy (BRELIBS) can be applied to analyze numerous transparent target types such as different glass types, gemstone, plastics, polymers, etc.