Raman amplification in plasma: thermal effects and damping

J. P. Farmer; B. Ersfeld; G. Raj; D. A. Jaroszynski

doi:10.1117/12.820566

7 May 2009 Raman amplification in plasma: thermal effects and damping

J. P. Farmer, B. Ersfeld, G. Raj, D. A. Jaroszynski

Proceedings Volume 7359, Harnessing Relativistic Plasma Waves as Novel Radiation Sources from Terahertz to X-Rays and Beyond; 73590M (2009) https://doi.org/10.1117/12.820566
Event: SPIE Optics + Optoelectronics, 2009, Prague, Czech Republic

Abstract

The role of thermal effects on Raman amplification are investigated. The direct effects of damping on the process are found to be limited, leading only to a decrease from the peak output intensity predicted by cold plasma models. However, the shift in plasma resonance due to the Bohm-Gross shift can have a much larger influence, changing the required detuning between pump and probe and introducing an effective chirp through heating of the plasma by the pump pulse. This "thermal chirp" can both reduce the efficiency of the interaction and alter the evolution of the amplified probe, avoiding the increase in length observed in the linear regime without significant pump depletion. The influence of this chirp can be reduced by using a smaller ratio of laser frequency to plasma frequency, which simultaneously increases the growth rate of the probe and decreases the shift in plasma resonance. As such, thermal effects only serve to suppress the amplification of noise at low growth rates. The use of a chirped pump pulse can be used to suppress noise for higher growth rates, and has a smaller impact on the peak output intensity for seeded amplification. For the parameter ranges considered, Landau damping was found to be negligible, as Landau damping rates are typically small, and the low collisionality of the plasma causes the process to saturate quickly.

Citation Download Citation

J. P. Farmer, B. Ersfeld, G. Raj, and D. A. Jaroszynski "Raman amplification in plasma: thermal effects and damping", Proc. SPIE 7359, Harnessing Relativistic Plasma Waves as Novel Radiation Sources from Terahertz to X-Rays and Beyond, 73590M (7 May 2009); https://doi.org/10.1117/12.820566

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KEYWORDS

Plasma

Thermal effects

Raman spectroscopy

Thermal modeling

Laser scattering

Photons

Wave propagation

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