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Title: Beam cleaning of an incoherent laser via plasma Raman amplification

Abstract

We show that backward Raman amplification in plasma can efficiently compress a temporally incoherent pump laser into an intense coherent amplified seed pulse, provided that the correlation time of the pump is longer than the inverse plasma frequency. One analytical theory for Raman amplification using pump beams with different correlation functions is developed and compared to numerical calculations and particle-in-cell simulations. Since incoherence on scales shorter than the instability growth time suppresses spontaneous noise amplification, we point out a broad regime where quasi-coherent sources may be used as efficient low-noise Raman amplification pumps. As the amplified seed is coherent, Raman amplification provides an additional a beam-cleaning mechanism for removing incoherence. At near-infrared wavelengths, finite coherence times as short as 50 fs allow amplification with only minor losses in efficiency.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [2]
  1. Princeton Univ., NJ (United States). Dept. of Mechanical and Aerospace Engineering
  2. Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1395338
Grant/Contract Number:
1506372; FA9550-15-1-0391; NA0002948
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 10; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Edwards, Matthew R., Qu, Kenan, Mikhailova, Julia M., and Fisch, Nathaniel J. Beam cleaning of an incoherent laser via plasma Raman amplification. United States: N. p., 2017. Web. doi:10.1063/1.4997246.
Edwards, Matthew R., Qu, Kenan, Mikhailova, Julia M., & Fisch, Nathaniel J. Beam cleaning of an incoherent laser via plasma Raman amplification. United States. doi:10.1063/1.4997246.
Edwards, Matthew R., Qu, Kenan, Mikhailova, Julia M., and Fisch, Nathaniel J. 2017. "Beam cleaning of an incoherent laser via plasma Raman amplification". United States. doi:10.1063/1.4997246.
@article{osti_1395338,
title = {Beam cleaning of an incoherent laser via plasma Raman amplification},
author = {Edwards, Matthew R. and Qu, Kenan and Mikhailova, Julia M. and Fisch, Nathaniel J.},
abstractNote = {We show that backward Raman amplification in plasma can efficiently compress a temporally incoherent pump laser into an intense coherent amplified seed pulse, provided that the correlation time of the pump is longer than the inverse plasma frequency. One analytical theory for Raman amplification using pump beams with different correlation functions is developed and compared to numerical calculations and particle-in-cell simulations. Since incoherence on scales shorter than the instability growth time suppresses spontaneous noise amplification, we point out a broad regime where quasi-coherent sources may be used as efficient low-noise Raman amplification pumps. As the amplified seed is coherent, Raman amplification provides an additional a beam-cleaning mechanism for removing incoherence. At near-infrared wavelengths, finite coherence times as short as 50 fs allow amplification with only minor losses in efficiency.},
doi = {10.1063/1.4997246},
journal = {Physics of Plasmas},
number = 10,
volume = 24,
place = {United States},
year = 2017,
month = 9
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on September 25, 2018
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  • A statistical model for forward stimulated-Brillouin scattering is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. The threshold above which the laser beam spatial incoherence cannot prevent the coherent growth of forward stimulated-Brillouin scattering is computed. It is found to be well below the threshold for self-focusing. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of propagation through a plasma of a spatially incoherent laser beam.
  • No abstract prepared.
  • Experiments are described in which a 1mJ, 1ps, 1200 nm seed laser beam is amplified by interaction with an intersecting 350 J, 1ns, 1054 nm pump beam in a low density (1 x 10{sup 19}/cm{sup 3}) plasma. The transmission of the seed beam is observed to be enhanced by > {approx} 25 x when the plasma is near the resonant density for stimulated Raman scattering (SRS), compared to measured transmissions at wavelengths just below the resonant value. The amplification is observed to increase rapidly with increases in both pump intensity and plasma density.
  • Experiments are described in which a 1mJ, 1ps, 1200 nm probe laser beam is amplified by interaction with an intersecting 350 J, 1ns, 1054 nm pump beam in a low density ({approx} 9 x 10{sup 24}/m{sup 3}) plasma. The transmission of the probe beam is observed to be enhanced by >{approx} 25 x when the plasma is near the resonant density for stimulated Raman scattering (SRS), as compared with measured transmissions at wavelengths just above the resonant value. The amplification is observed to increase rapidly with increases in both pump intensity and plasma density.
  • The recently proposed scheme of so-called ''fast compression'' of laser pulses in plasma can increase peak laser intensities by 10{sup 5} [Phys. Rev. Lett. 82, 4448 (1999)]. The compression mechanism is the transient stimulated Raman backscattering, which outruns the fastest filamentation instabilities of the pumped pulse even at highly overcritical powers. This Letter proposes a novel nonlinear filtering effect that suppresses premature backscattering of the pump in a noisy plasma layer, while the desired amplification of a sufficiently intense seed persists with a high efficiency. The effect is of basic interest and also makes it robust to noise the simplestmore » technologically fast compression scheme. (c) 2000 The American Physical Society.« less