X-ray characterisation in high-intensity laser-solid interactions

When a high intensity laser pulse collides with a solid target, the electric fields present are strong enough to ionise the solid atoms, creating a plasma of ions and electrons on the target surface. The acceleration of these plasma electrons in the laser fields produce X-rays via the non-linear Compton scatter (NCS) process. While it is expected that NCS may provide a highly efficient source of X-rays in next generation laser facilities, and may also act as a diagnostic for the electron motion within the laser, we have not yet observed this process in laser-solid interactions at the lower intensities reached by modern lasers. This is due to a background of bremsstrahlung radiation, produced as plasma electrons scatter in the electric fields of the solid target nuclei.

This work attempts to characterise the NCS and bremsstrahlung X-rays produced in laser-solid interactions, and to find NCS signatures which would allow for experimental identification of this process. This will be accomplished by adding the capability to simulate bremsstrahlung radiation to the particle-in-cell code EPOCH. Large scale laser-solid interaction simulations will be run to study the expected X-ray distributions over a variety of laser/solid parameters to identify angular/spectral differences between the two radiation mechanisms.

A single particle model has been developed to analytically describe electron sheets moving through an immobile ion channel. This simple framework will be tested against EPOCH simulations to determine it's applicability, and may be used to describe the expected form of the NCS emission in laser-solid interactions. If successful, further applications of this code could help develop a source of X-ray pulses on the attosecond timescale