Temporally Resolved Optical Probing of Laser Propagation in Underdense and Near-Critical Density Plasmas on Picosecond Timescales*

Experimentally probing the fast evolving nature of intense, short pulse laser-plasma interactions remains an important challenge that is crucial to understanding interaction dynamics. Transverse optical probe techniques are commonly used to characterise changes to plasma density and ionisation induced in plasma at a single point in time. Building a profile of these characteristics evolving requires many repeat shots over which the probe time is varied. This approach is inherently susceptible to shot-to-shot variations in the drive laser parameters and therefore can fail to provide reliable insight into the evolution of the interaction. Using a new 4-channel optical probe, with picosecond temporal resolution, we demonstrate 2D multi-frame measurements of plasma processes from a single intense laser pulse.

In an experiment using the Vulcan laser system at the Rutherford Appleton Laboratory, we have applied this new approach to investigate intense laser propagation in underdense and near-critical density plasmas. The development of this diagnostic technique will be presented, together with results from an investigation into the dynamics of laser self-focusing and filamentation in an underdense plasma.