Investigation of the early-stage dynamics of laser-produced plasma using collective Thomson scattering

Plasma temperature, density and flow velocity are the critical physical properties of Laser produced plasmas (LPP) to reveal the ablation mechanism, energy transport and hydrodynamic evolution. In the time window during and just after the ablation irradiation, experimental data are very scarce so that many theoretical models remain untested. In this study, we give a concise evolution history of LPP expansion within 0 to 14 ns after the ablation peak. Electron density (n_e) , temperature (T_e) and drift velocity (V_d) in LPPs are measured using ion feature of collective Thomson scattering (CTS).

Spatial-resolved results show LPP is nearly isothermal during the ablation pulse. Investigations on velocity reveal LPP expands predominantly perpendicular to the surface, in which direction the drift velocity increase linearly with distance. Importantly, LPP has a considerable initial velocity at the target surface, approximately the sound speed derived from the local T_e. Our results suggest the self-similar isothermal model can better describe the LPP behavior in this initial time than the adiabatic ones. In this scenario, a structure that transport thermal energy by electron conduction should exist, between the cutoff density and ablation front.