Double-pulse femtosecond laser ablation of the surface of stainless steel with variable interpulse delays

Spectral studies of optical emission from plumes produced via ablation of the surface of stainless steel in the phase explosion regime at different incident fluences by a pair of collinear degenerate femtosecond laser pulses, separated by variable delay time of 0.01–1.5 ns, demonstrate a drastic decrease in atomic emission intensities in a subnanosecond range. This effect was related to “bulk” absorption of the second pump pulse in ablative plumes with near-critical density, achieved during their hydrodynamic expansion on a subnanosecond timescale.