Expansion dynamics and compression layer in collinear double-pulse laser produced plasmas in a vacuum

Collinear double-pulse (DP) laser-produced plasmas (LPP) of Al in a vacuum under a nanosecond–picosecond configuration were investigated. Combining fast imaging and laser interferometry, expansion profiles and electron density distributions of single pulse (SP) and nanosecond–picosecond collinear DP-LPP with inter-pulse time intervals of 20, 30, and 50 ns were obtained and their evolution characteristics were analyzed. A compression layer was observed during plasma expansion; both its shape and density distribution were controllable by varying the inter-pulse time interval. A special crescent-shaped compression layer was obtained, indicating that a special state of plasma had been prepared by collinear DP-LPP. The results of this study are helpful to a further understanding of expansion and evolution characteristics of collinear DP-LPP and provide an experimental basis for the development of a related theoretical model.