Propagation of Hermite cosh Gaussian laser beam in free electron laser device under upward plasma density ramp

Abstract This paper analyses the propagation of a Hermite cosh Gaussian laser beam into the free electron laser (FEL) device inside a plasma with an upward density ramp. The dispersion relation is derived using linear fluid theory. A detailed analysis of its characteristics, such as changes in growth rate attributing to both Compton and Raman regimes and the energy exchange efficiency has been investigated. Further, the growth rate characteristics have been observed for varying decentered parameter and mode index values. The result analysis shows, enhanced energy transfer at high plasma densities and an increase in frequency of radiation emission in the Raman regime, attributable to increased scattering and interaction facilitated by the upward plasma density ramp. The increase in normalized energy gain with beam voltage highlights the improved energy transfer efficiency in the FEL, emphasizing the value of higher voltages for maximum energy gain. This paves way to efficient interaction and improved tunability, enabling the operation of FELs at increased beam voltages, resulting in the generation of high-frequency radiation.