Observation of dual-peak signal-to-noise ratios from plasmas produced in typical laser-induced breakdown spectroscopy (LIBS) experiments

Abstract

In this work, emission properties of representative trace and major species in steel plasma plumes produced in typical laser-induced breakdown spectroscopy (LIBS) experiments under standard atmospheric conditions are investigated. The correlation between laser fluence and spatially integrated measurements of emission characteristics of the plasma at a typical delay time of 2 µs from the laser pulse onset is thoroughly explored. Q-switched neodymium-doped yttrium aluminum garnet (Nd: YAG) laser emitting at its fundamental wavelength of 1064 nm was employed to generate the plasmas under investigation. The results showed that the signal-to-noise ratio of all lines investigated exhibit irregular behaviour in which two maxima can be identified at specific laser fluence values. This behaviour is attributed to lower standard deviation of the background intensity indicating stable plasma conditions relevant for spectrochemical analysis. Plasma shielding of the incident laser energy, due to electron-atom inverse bremsstrahlung (IB), becomes more critical beyond laser fluencies larger than about 45 J cm-2.