Experimental measurements of relativistically induced transparency at BELLA iP2*

Petawatt laser systems provide researchers access to the relativistic transparency regime for solid density targets. Ongoing work in particle acceleration and laser energy absorption shows that the relativistically induced transparency regime is important to the future of laser-plasma physics. Analytical theory provides an approximation for the onset-time to relativistic transparency in thin foils, but there is a lack of experimental data that supports the model. At the BELLA Center’s iP2 beamline, we developed a suite of optical diagnostics to characterize the transmitted and reflected light from a high intensity (>10²¹ W/cm²) laser plasma interaction on silicon nitride membranes and near-critical density foams. A frequency resolved optical gating (FROG) device measured the temporal and spectral profiles of the reflected light, while the transmitted light was measured by a GRENOUILLE device and spectrometer. Additional diagnostics were used to verify the high intensity laser pulse interacted with an overdense plasma. We present preliminary experimental data showing the temporal and spectral changes to the laser pulse as it relativistically interacts with the various targets, and how it compares to the most recent theoretical predictions.