Optical probing of high intensity laser propagation through plasma
This thesis studies the propagation of high intensity lasers through underdense plasmas and the subsequent channel formation. This comprises experimental studies of hole boring mechanism in laser plasma interactions, as well as simulations relevant to these experiments. The experiments described were conducted at the Rutherford Appleton Laboratory (January- April 2009) utilising the Vulcan laser facility. A chapter is dedicated to the characterisation of gas jets used for the channelling experiments. This chapter gives a study of gas flows using different supersonic nozzles and theoretical background that is applicable to laser plasma experiments described later. The major experimental chapter presents, the production of relativistic electron with the interaction of high intensity lasers (1 ps) with under dense plasmas. The experimental results and simulations show that the ponderomotive force of the laser pulse produces an ion channel due to the expulsion of electrons. The interaction of the laser field with the focusing force of the channel leads to significant electron acceleration with energies up to 200 MeV. The final experimental chapter investigates channel creation in deuterium gas jets at varying plasma densities ( 1018 cm−3 - 1020 cm−3), using laser pulses with parameters for the hole-boring phase of the Fast Ignitor scheme of inertial confinment fusion ( τ ~ 30 ps,I = 1018 Wcm−2). The ponderomotive force and relativistic effects cause the laser pulse to self-focus. These effects can guide the laser pulse through the plasma over many Rayleigh lengths. The generation of energetic electrons (~ MeV) was also observed, but with relatively little dependence on density. The experimental data has been also illustrated by simulations, which exhibit good agreement with experimental results for the channel formation.