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Title: Coupling of laser energy into plasma channels

Abstract

Diffractive spreading of a laser pulse imposes severe limitations on the acceleration length and maximum electron energy in the laser wake field accelerator (LWFA). Optical guiding of a laser pulse via plasma channels can extend the laser-plasma interaction distance over many Rayleigh lengths. Energy efficient coupling of laser pulses into and through plasma channels is very important for optimal LWFA performance. Results from simulation parameter studies on channel guiding using the particle-in-cell (PIC) code VORPAL [C. Nieter and J. R. Cary, J. Comput. Phys. 196, 448 (2004)] are presented and discussed. The effects that density ramp length and the position of the laser pulse focus have on coupling into channels are considered. Moreover, the effect of laser energy leakage out of the channel domain and the effects of tunneling ionization of a neutral gas on the guided laser pulse are also investigated. Power spectral diagnostics were developed and used to separate pump depletion from energy leakage. The results of these simulations show that increasing the density ramp length decreases the efficiency of coupling a laser pulse to a channel and increases the energy loss when the pulse is vacuum focused at the channel entrance. Then, large spot size oscillations resultmore » in increased energy leakage. To further analyze the coupling, a differential equation is derived for the laser spot size evolution in the plasma density ramp and channel profiles are simulated. From the numerical solution of this equation, the optimal spot size and location for coupling into a plasma channel with a density ramp are determined. This result is confirmed by the PIC simulations. They show that specifying a vacuum focus location of the pulse in front of the top of the density ramp leads to an actual focus at the top of the ramp due to plasma focusing, resulting in reduced spot size oscillations. In this case, the leakage is significantly reduced and is negligibly affected by ramp length, allowing for efficient use of channels with long ramps.« less

Authors:
; ; ; ; ; ; ;  [1];  [2];  [2]
  1. Tech-X Corporation, 5621 Arapahoe Avenue, Suite A, Boulder, Colorado 80303 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20974944
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2721068; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ACCELERATION; DIFFERENTIAL EQUATIONS; ELECTRONS; ENERGY LOSSES; IONIZATION; LASERS; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA SIMULATION; PLASMA WAVES; PULSES; TUNNEL EFFECT; WAKEFIELD ACCELERATORS

Citation Formats

Dimitrov, D. A., Giacone, R. E., Bruhwiler, D. L., Busby, R., Cary, J. R., Geddes, C. G. R., Esarey, E., Leemans, W. P., Tech-X Corporation, 5621 Arapahoe Avenue, Suite A, Boulder, Colorado 80303 and University of Colorado, Boulder, Colorado 80309, and Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720. Coupling of laser energy into plasma channels. United States: N. p., 2007. Web. doi:10.1063/1.2721068.
Dimitrov, D. A., Giacone, R. E., Bruhwiler, D. L., Busby, R., Cary, J. R., Geddes, C. G. R., Esarey, E., Leemans, W. P., Tech-X Corporation, 5621 Arapahoe Avenue, Suite A, Boulder, Colorado 80303 and University of Colorado, Boulder, Colorado 80309, & Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720. Coupling of laser energy into plasma channels. United States. doi:10.1063/1.2721068.
Dimitrov, D. A., Giacone, R. E., Bruhwiler, D. L., Busby, R., Cary, J. R., Geddes, C. G. R., Esarey, E., Leemans, W. P., Tech-X Corporation, 5621 Arapahoe Avenue, Suite A, Boulder, Colorado 80303 and University of Colorado, Boulder, Colorado 80309, and Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720. Sun . "Coupling of laser energy into plasma channels". United States. doi:10.1063/1.2721068.
@article{osti_20974944,
title = {Coupling of laser energy into plasma channels},
author = {Dimitrov, D. A. and Giacone, R. E. and Bruhwiler, D. L. and Busby, R. and Cary, J. R. and Geddes, C. G. R. and Esarey, E. and Leemans, W. P. and Tech-X Corporation, 5621 Arapahoe Avenue, Suite A, Boulder, Colorado 80303 and University of Colorado, Boulder, Colorado 80309 and Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720},
abstractNote = {Diffractive spreading of a laser pulse imposes severe limitations on the acceleration length and maximum electron energy in the laser wake field accelerator (LWFA). Optical guiding of a laser pulse via plasma channels can extend the laser-plasma interaction distance over many Rayleigh lengths. Energy efficient coupling of laser pulses into and through plasma channels is very important for optimal LWFA performance. Results from simulation parameter studies on channel guiding using the particle-in-cell (PIC) code VORPAL [C. Nieter and J. R. Cary, J. Comput. Phys. 196, 448 (2004)] are presented and discussed. The effects that density ramp length and the position of the laser pulse focus have on coupling into channels are considered. Moreover, the effect of laser energy leakage out of the channel domain and the effects of tunneling ionization of a neutral gas on the guided laser pulse are also investigated. Power spectral diagnostics were developed and used to separate pump depletion from energy leakage. The results of these simulations show that increasing the density ramp length decreases the efficiency of coupling a laser pulse to a channel and increases the energy loss when the pulse is vacuum focused at the channel entrance. Then, large spot size oscillations result in increased energy leakage. To further analyze the coupling, a differential equation is derived for the laser spot size evolution in the plasma density ramp and channel profiles are simulated. From the numerical solution of this equation, the optimal spot size and location for coupling into a plasma channel with a density ramp are determined. This result is confirmed by the PIC simulations. They show that specifying a vacuum focus location of the pulse in front of the top of the density ramp leads to an actual focus at the top of the ramp due to plasma focusing, resulting in reduced spot size oscillations. In this case, the leakage is significantly reduced and is negligibly affected by ramp length, allowing for efficient use of channels with long ramps.},
doi = {10.1063/1.2721068},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • No abstract prepared.
  • We report coupling and guiding of pulses of peak power up to 0.3 TW in 1.5-cm-long preformed plasma waveguides, generated in a high repetition rate argon gas jet. Coupling of up to 52{percent} was measured for 50-mJ, {approximately}110-fs pulses injected at times longer than 20 ns, giving guided intensities up to {approximately}5{times}10{sup 16} W/cm{sup 2}. For short delays between waveguide generation and pulse injection, pulse shortening occurred, with this effect reduced either by increasing delay or injecting a prepulse into the waveguide. There is excessive taper at the waveguide ends, which results from reduced heating at the ends of themore » jet by the waveguide generation pulse. {copyright} {ital 1999} {ital The American Physical Society}« less
  • We report coupling and guiding of pulses of peak power up to 0.3 TW in 1.5 cm long preformed plasma waveguides generated in a high repetition rate argon gas jet. Coupling of up to 52{percent} was measured for 50 mJ, {minus}110 fs pulses injected at times longer than 20 ns, giving guided intensities up to {minus}5{times}10{sup 16}&hthinsp;W/cm{sup 2}. It was found that for short delays between waveguide generation and pulse injection, pulse shortening occurred, with this effect reduced as delay was increased. Injection into the waveguide of two consecutive pulses separated by a few nanoseconds resulted in the reduction ofmore » shortening of the second pulse at all delays. Femtosecond time-resolved shadowgrams of the coupling of injected pulses into the waveguide show that there is {approximately}0.5 mm of neutral gas remaining at the waveguide entrance after waveguide generation. {copyright} {ital 1999 American Institute of Physics.}« less
  • The guiding of intense laser pulses in plasma channels is necessary to maximize the energy of electrons accelerated in a laser wakefield accelerator. A significant fraction of the energy in the laser pulse may be lost during and after coupling from vacuum into a channel. For example, imperfect coupling can lead to enhanced leakage of laser energy transversely through the channel walls. We present 2D particle-in-cell (PIC) simulations, using the VORPAL code, of an example problem. We present a numerical diagnostic, based on simultaneous FFT's in space and time, which enables quantitative measurements of forward and backward propagating pulse energymore » and its spectra. Future work will be directed toward VORPAL parameter studies designed to optimize the amount of laser energy that couples into a channel.« less
  • We report coupling and guiding of pulses of peak power up to 0.3 TW in 1.5 cm long preformed plasma waveguides generated in a high repetition rate argon gas jet. Coupling of up to 52% was measured for 50 mJ, -110 fs pulses injected at times longer than 20 ns, giving guided intensities up to -5x10{sup 16} W/cm{sup 2}. It was found that for short delays between waveguide generation and pulse injection, pulse shortening occurred, with this effect reduced as delay was increased. Injection into the waveguide of two consecutive pulses separated by a few nanoseconds resulted in the reductionmore » of shortening of the second pulse at all delays. Femtosecond time-resolved shadowgrams of the coupling of injected pulses into the waveguide show that there is {approx}0.5 mm of neutral gas remaining at the waveguide entrance after waveguide generation.« less