Observation and characterization of laser driven shock waves in tenuous plasma

The observation and characterization of collisionless shock waves generated in laser plasma interactions is presented. The shock waves are generated by long pulse ~lns, intense (10 ¹⁵Wycm ²) laser irradiation of solid targets and are observed to propagate in a tenuous (10 ¹³ - ¹⁶cm ^-3), non magnetized background plasma. These nonlinear entities are detected and characterized by employing a proton imaging technique, which allows the simultaneous detection of propagation velocity, width of the shock front and electrostatic field associated with the shock, with high spatial and temporal resolution. Ion Acoustic Solitons (IAS) were observed under certain conditions and as inferred from the reconstructed associated electric field profile. The variation of IAS velocity and width as a function of the ambient parameters was characterized. The data show an increase in velocity and decrease in width as the density of the background plasma (generated via photo ionization of controlled, low density gas in a gas cell) is increased. The experimental results are interpreted in the frame work of Korteweg-de Vries nonlinear wave description and in agreement with theoretical predications.