Backward-propagating MeV electrons from 1018 W/cm2 laser interactions with water
Abstract
We present an experimental study of the generation of ∼MeV electrons opposite to the direction of laser propagation following the relativistic interaction at normal incidence of a ∼3 mJ, 1018 W/cm2 short pulse laser with a flowing 30 μm diameter water column target. Faraday cup measurements record hundreds of pC charge accelerated to energies exceeding 120 keV, and energy-resolved measurements of secondary x-ray emissions reveal an x-ray spectrum peaking above 800 keV, which is significantly higher energy than previous studies with similar experimental conditions and more than five times the ∼110 keV ponderomotive energy scale for the laser. We show that the energetic x-rays generated in the experiment result from backward-going, high-energy electrons interacting with the focusing optic, and vacuum chamber walls with only a small component of x-ray emission emerging from the target itself. We also demonstrate that the high energy radiation can be suppressed through the attenuation of the nanosecond-scale pre-pulse. These results are supported by 2D particle-in-cell simulations of the laser-plasma interaction, which exhibit beam-like backward-propagating MeV electrons.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2015
- Source ID
- 10.1063/1.4916493
Entities
People
- Chris Orban
- Enam Chowdhury
- J. T. Morrison
- John Nees
- Kyle Frische
- R. R. Freeman
- Scott Feister
- V. M. Ovchinnikov
- W. M. Roquemore
Organizations
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- National Academies of Sciences, Engineering, and Medicine
- Ohio State University
- University of Michigan