Time-resolved studies of colliding laser-produced plasmas

This thesis presents work done on investigating colliding laser-produced plasmas with time-resolved, UV-visible spectroscopy and time-resolved visible imaging. A nanosecond Nd:YAG laser pulse was split with a wedge prism and the two laser pulses created were focused onto the target surface, with power densities of ϕ = 1:6 x 10^12 W/cm2. The separation between the two plasmas was 2.6 mm and in between them a stagnation layer was formed. Plasmas of silicon (Si, Z=14), tin (Sn, Z=50) and lead (Pb, Z=82) were investigated. Time-resolved spectroscopy was used to determine the expansion velocities for different ion stages of Si and Pb, for both single plasmas as well as in the case where two plasmas collided to yield stagnation layers. Time-resolved visible imaging was used to obtain the expansion velocities of both seed plasmas and stagnation layers plasma-plume front. Colliding plasmas of different elements, Pb and Si, were studied and expansion velocities of different ion stages were compared with those obtained for colliding two identical plasmas. Acceleration of ions due to an electric potential difference is observed in the stagnation layer. Obtaining information about expansion velocities of different ion species provides great insight into the dynamics of laser-produced plasma expansion. Charge and time resolved dynamics have not been used before to study stagnation layers.