Spectro-temporal comparisons of optical emission, absorption, and laser-induced fluorescence for characterizing ns and fs laser-produced plasmas

We performed simultaneous measurement of absorption, emission, and laser-induced fluorescence spectroscopic signatures for determining nanosecond and femtosecond laser-produced plasma's (LPP) physical properties throughout its lifecycle. Plasmas are produced by focusing either similar to 6 ns, 1064 nm pulses from an Nd:YAG or similar to 35 fs, similar to 800 nm pulses from a Ti:sapphire laser on an Inconel target that contains Al as a minor alloying addition. A continuous-wave narrowband tunable laser was used for performing absorption and fluorescence spectroscopy while a fast-gated detection system was used for emission spectroscopy. The temporal evolution of emission, fluorescence, and absorbance of Al transitions are compared for both ns and fs LPPs. Time-resolved absorbance was also used for evaluating linewidth, lineshape, temperature, and column-averaged atomic number density at late times of ns and fs plasma evolution. Our results demonstrate that lower and excited-state populations of fs LPPs are short-lived in comparison to those in ns plasmas. The lower state population is observed to reach a maximum value earlier in time for the fs plasma versus the ns plasma, while the kinetic temperature for the ns plasma was higher than for the fs plasma at most times of the plasma evolution.

Automated summary

In this study, simultaneous measurement of absorption, emission, and laser-induced fluorescence spectroscopic signatures was performed to determine the physical properties of nanosecond and femtosecond laser-produced plasma throughout its lifecycle. The results show that lower and excited-state populations in femtosecond laser-produced plasma are short-lived compared to those in nanosecond plasmas. Additionally, the kinetic temperature for nanosecond plasma was higher than for femtosecond plasma at most times of the plasma evolution.