Dynamics of ultrafast laser plasma expansion in the presence of an ambient.

We investigated the role of ambient gas pressure on the expansion and the emission features during ultrafast laser ablation of metal target. Plasma plumes were generated using 800 nm, 40 fs laser pulses on a copper target and the ambient air pressure was varied more than seven orders (1 × 10-5 - 760 Torr) of magnitude. Fast-gated images showed a complex interaction between the plume and ambient leading to changes in the plume geometry with pressure as well as time. The ambient pressure levels are found to affect both the line intensities and broadening along with signal to noise (S/N) and signal to background (S/B) ratios. The optimum pressure condition for analytical applications is found to be ∼100 Torr. [ABSTRACT FROM AUTHOR]