Simulation and Experimental Measurements of Relativistic Transparency in Plasmas with Ultrafast High Intensity Laser Pulses*

A LaserNetUS experiment was conducted at the Scarlet Laser Facility (λ = 800 nm, 35 fs), investigating Relativistic Transparency (RT) in ultrafast high intensity laser plasma interactions. In a strong electric field, electrons oscillate at relativistic speeds which alters the plasma frequency by the Lorentz gamma factor, resulting in an intensity-dependent relativistic critical density; what is classically an overdense plasma is now transparent to the incident laser light.

The targets were 8CB liquid crystal films with thicknesses varied between 20-100 nm and the laser intensity scanned over the range 10^19­-10²¹ W/cm². Transmitted and reflected energy were measured by imaged screens. The results are compared with 2D and 3D particle-in-cell OSIRIS 4.0 simulations to identify experimental preplasma conditions. We present our work showing a clear trend in transmitted light vs target thickness, as well as an asymmetric spatial profile of the transmitted and reflected light. The analysis compares the experimental results to the most recent theory for onset time to RT.