The Raman gap and collisional absorption

Ido Barth*, Pierre Michel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


One of the long-standing puzzles observed in many laser-plasma experiments is the gap in the Raman backscattering spectrum. This gap is characterized by the absence of backscattered light between some critical wavelength and twice the incident laser wavelength. The latter is associated with the absolute Raman instability from the quarter-critical density surface. Supported by particle-in-cell (PIC) simulations, it is suggested that the gap can result from the collisional damping of the backscattered light. A linear analysis of the competition between the Raman growth rate and the damping rate in a non-homogenous plasma predicts the gap's existence and width as a function of the system's parameters. The theory is compared with the PIC simulations and past experiments.

Original languageAmerican English
Article number012109
JournalPhysics of Plasmas
Issue number1
StatePublished - 1 Jan 2024

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