Measurement of the Ponderomotive Filamentation Instability Growth Rate in Short-Pulse Laser Beams

In ponderomotive filamentation instability, the ponderomotive ejection of electrons from the high-intensity regions of a laser beam causes modulations to the plasma density and refractive index, which lead to self-focusing and filamentation. We present an experiment that utilizes the joint operation of the OMEGA 60 and OMEGA EP Laser Systems at the University of Rochester’s Laboratory for Laser Energetics to investigate the growth rate of the ponderomotive filamentation instability. In our experiment, a 1w short-pulse (100-ps) laser beam from OMEGA EP is coupled into a preheated plasma on the OMEGA 60 laser–plasma interaction platform. The beam spray of the filamented short-pulse beam is recorded as a time-integrated 2-D image and a time-resolved 1-D image utilizing a specially made infrared transmitted beam diagnostic and coupled streak camera. The measured radial-growth rate is then compared with theoretical predictions and scaling with incident beam intensity and plasma temperature. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856 and the Office of Fusion Energy under Award Numbers DE-SC0016253 and DE-SC00215057.