D. Kuk

Non-Maxwellian electron distributions resulting from direct laser acceleration in near-critical plasmas

The irradiation of few nm thick targets by a finite-contrast high-intensity short-pulse laser results in a strong pre-expansion of these targets at the arrival time of the main pulse. The targets decompress to near and lower than critical densities plasmas extending over few micrometers, i.e. multiple wavelengths. The interaction of the main pulse with such a highly localized but inhomogeneous target leads to the generation of a short channel and further self-focusing of the laser beam. Experiments at the GHOST laser system at UT Austin using such targets measured non-Maxwellian, peaked electron distribution with large bunch charge and high electron density in the laser propagation direction. These results are reproduced in 2D PIC simulations using the EPOCH code, identifying Direct Laser Acceleration (DLA) as the responsible mechanism. This is the first time that DLA has been observed to produce peaked spectra as opposed to broad, maxwellian spectra observed in earlier experiments. This high-density electrons have potential applications as injector beams for a further wakefield acceleration stage as well as for pump-probe applications.

Full-aperture backscatter diagnostics and applications at the Texas Petawatt Laser facility

In this paper, we present the development and application of a full-aperture backscatter diagnostics system at the Texas Petawatt Laser (TPW) facility. The diagnostic system includes three independent diagnostic stations. With this system, we obtained TPW on-shot focus properties, and high-harmonic spectral emission from solid foils (e.g., Cu and Al) and their Si substrate in an experiment to study laser hole boring, which show the hole-boring mechanism at relativistic intensities. The measured on-target full-power focal spots from ultrathin film targets help determine the optimum target thickness at certain laser contrast parameters for particle acceleration and neutron generation experiment, which is also a relative measurement of shot-toshot intensity fluctuations.

Measurement of the equation of state of solid-density copper heated with laser-accelerated protons

We present equation of state (EOS) measurements of solid-density copper heated to 5-10 eV. A copper sample was heated isochorically by hydrogen ions accelerated from an adjacent foil by a high intensity pulsed laser, and probed optically. The measured temperature and expansion are compared against simulations using the most up-to-date wide range EOS tables available.

Laser generation of ultra-short neutron bursts from high atomic number converters

At the Texas Petawatt laser facility we developed a novel ultra-short pulsed laser-driven neutron source generating an unprecedented output peak flux. Our results show a dramatic onset of high-energy electron generation from petawatt laser-irradiated plastic targets for targets thinner than a few microns. In this regime, the copious amounts of multi-MeV electrons emitted from the target are utilized to generate photo-neutrons from a metal converter. The neutrons are generated with a <50 ps pulse duration and a flux of 1018 n/cm2/s, exceeding any other pulsed or CW neutron source. In this paper, we will report on our measurement of the neutron yields produced from high atomic number converters.

All-reflective Ti:Sa power amplifier for Petawatt laser

An all-reflective Ti:Sa power amplifier capable of extracting up to 60 joules has been designed. The power amplifier consists of four passes through a 100mm Ti:Sa crystal really imaged by off-axis parabolas enclosed in a vacuum chamber.