Ultrashort PW laser pulse interaction with target and ion acceleration

TL;DR

This paper reports experimental findings on ion acceleration using petawatt femtosecond laser interactions with aluminum targets, revealing how laser intensity and focal spot size influence ion energy and flux directions, with implications for applications.

Contribution

It provides new experimental data on ion acceleration at high laser intensities, exploring the effects of laser parameters on ion energy scaling and flux distribution in laser-solid interactions.

Findings

Ion energy scales as I^0.8 along the rear surface and I^0.6 along the front surface.

Proton energy depends more on laser energy than focal spot size.

Backward proton flux increases with laser intensity, approaching parity with forward flux.

Abstract

We present the experimental results on ion acceleration by petawatt femtosecond laser solid interaction and explore strategies to enhance ion energy. The irradiation of micrometer thick (0.2 - 6.0 micron) Al foils with a virtually unexplored intensity regime (8x10^19 W/cm^2 - 1x10^21 W/cm^2) resulting in ion acceleration along the rear and the front surface target normal direction is investigated. The maximum energy of protons and carbon ions, obtained at optimised laser intensity condition (by varying laser energy or focal spot size), exhibit a rapid intensity scaling as I^0.8 along the rear surface target normal direction and I^0.6 along the front surface target normal direction. It was found that proton energy scales much faster with laser energy rather than the laser focal spot size. Additionally, the ratio of maximum ion energy along the both directions is found to be constant for the broad range of target thickness and laser intensities. A proton flux is strongly dominated in the forward direction at relatively low laser intensities. Increasing the laser intensity results in the gradual increase in the backward proton flux and leads to almost equalisation of ion flux in both directions in the entire energy range. These experimental findings may open new perspectives for applications.