Laser-driven beams of fast ions, relativistic electrons and coherent x-ray photons

Abstract: This thesis presents experimental results on the development and optimization of novel and highly compact sources of beams of fast ions, relativistic electrons and coherent x-rays, driven by intense laser-plasma interactions.

The rapid development of high-power, short-pulse laser systems have made available peak powers reaching the petawatt regime and focused intensities reaching 10^21 W/cm2. When interacting with matter, the extreme energy density (several GJ/cm3) associated with the focused laser pulses can create exceptionally high quasi-stationary electric fields, beyond several teravolt-per-meter (TV/m). By careful selection of the interaction conditions, electrons, protons or heavy ions can be accelerated to the multi-MeV kinetic energy level in distances ranging from a only a few micrometers up to several centimeters.

The thesis addresses three important topics and summarizes results obtained using the multi-terawatt laser at the Lund Laser Centre in Sweden and the Vulcan Petawatt laser at the Rutherford-Appleton Laboratory in the United Kingdom.

The thesis discusses laser-plasma acceleration of protons and heavy ions from thin foil metallic targets. The ion energy scalings with laser pulse and target parameters are investigated, and protons have been accelerated up to 55 MeV. Ultrathin targets, with thicknesses below 100 nm, and ultrahigh contrast laser pulses are shown to substantially enhance the proton maximum energy and laser-to-particle beam conversion efficiency. Shock waves, launched by the intrinsic laser prepulse, are shown to significantly influence the acceleration mechanisms. Novel schemes, involving multiple laser pulses, for active control of the spatial energy distribution of the accelerated ion beams are also presented.

Results regarding the generation and optimization of quasi-monoenergetic electron beams are presented. Acceleration occurs in a plasma wave that is excited in the wake of an intense laser pulse in a tenuous plasma. Electrons are accelerated up to 200 MeV in less than 2 mm acceleration length. It is shown that, in the quasi-monoenergetic regime, electrons originate from the first plasma wave period. Current challenges such as electron beam stability are also specifically addressed.

The thesis also reports the implementation of a laser in the soft x-ray regime. By using a grazing incidence pumping scheme, picosecond x-ray laser pulses with energies up to 3 uJ at a wavelength of 18.9 nm are produced at 10 Hz repetition rate, using Ni-like molybdenum ions as amplifying medium.