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.