Description
The Fourth-generation Laser for Ultrabroadband eXperiments (FLUX) was recently activated at the Laboratory for Laser Energetics to study the effects of laser bandwidth on laser-plasma instabilities. FLUX delivers a spectrally incoherent beam with 5 nm of bandwidth centered around 351 nm to the target chamber of the Omega Laser Facility. FLUX was initially used was used to demonstrate a novel plasma diagnostic that can measure spatially localized plasma conditions. By crossing the FLUX beam with a narrow 351-nm beam in a nitrogen/hydrogen plasma, a broadband electromagnetic beat wave excited ion-acoustic waves in a ~0.004 mm^3 volume was created. The response of the ion-acoustic waves to this beat wave was imprinted on the spectrum of the transmitted FLUX beam. The ion-acoustic resonances transfer energy between the FLUX beam and the narrow band beam (i.e., cross-beam energy transfer (CBET) moves energy between the two beams). The locations and width of the resonant peaks in the output spectrum provide a measure of the electron and ion temperature, respectively, and the magnitude of transfer was used to determine the plasma density. This technique provides an alternative to Thomson scattering and can have powerful advantages in many situations. It also greatly accelerates our ability to validate CBET models, because the entire CBET gain curve is now captured in a single shot. FLUX is poised to deliver data on laser-plasma instability suppression paving the way for next generation ICF designs. This work is supported by the Department of Energy under contract numbers: DE-NA-0004144 and DE-SC0024863.