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Title: Backward-propagating MeV electrons from 10{sup 18} W/cm{sup 2} laser interactions with water

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, 10{sup 18} W/cm{sup 2} 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.
Authors:
 [1] ;  [2] ;  [3] ; ;  [4] ; ;  [2] ;  [3] ;  [5] ;  [3] ;  [2] ;  [6]
  1. Fellow, National Research Council, Washington, District of Columbia 20001 (United States)
  2. Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)
  3. (United States)
  4. Innovative Scientific Solutions, Inc., Dayton Ohio 45459 (United States)
  5. Center for Ultra-fast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)
  6. Air Force Research Laboratory, Dayton, Ohio 45433 (United States)
Publication Date:
OSTI Identifier:
22408338
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 4; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; COMPUTERIZED SIMULATION; ELECTRON TRANSFER; ELECTRONS; FARADAY CUPS; INTERACTIONS; KEV RANGE; LASER RADIATION; MEV RANGE; PHOTON EMISSION; PONDEROMOTIVE FORCE; PULSES; RELATIVISTIC RANGE; TWO-DIMENSIONAL CALCULATIONS; WATER; X-RAY SPECTRA