Time-resolved absorption spectroscopic characterization of ultrafast laser-produced plasmas under varying background pressures

Time-resolved tunable laser absorption spectroscopy is used to characterize the physical properties of ultrafast laser-produced plasmas. The plasmas were produced from an Inconel target, with $\ensuremath{\le}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{wt}\phantom{\rule{0.16em}{0ex}}%$ Al, using $\ensuremath{\sim}35\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$, $\ensuremath{\sim}800\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}$ laser pulses at varying Ar background pressures from 1 to 100 Torr. The absorption spectrum of atomic Al is measured with high spectral and temporal resolution when the probe laser is stepped across the selected Al transition at 394.4 nm. Spectral fitting is used to infer linewidths, kinetic temperature, Al column density, and pressure broadening coefficient. The late time physical properties of plasmas are compared for various pressure levels. Our studies highlight that a significant lower state population exists even at early times of ultrafast laser-produced plasma evolution, and lower state population persistence decreases with increasing ambient pressure. We also show that the fundamental optical properties, such as pressure broadening, can be measured using ultrafast laser-produced plasmas combined with laser absorption spectroscopy.