Nonlinear saturation and efficiency enhancement in a Cherenkov laser using a dielectric grating

With the aid of particle simulation, this paper discusses nonlinear saturation and efficiency enhancement in a single-pass Cherenkov laser using a dielectric grating, taking into account the nonlinear properties of a relativistic electron beam. For the analysis of the problem, a two-dimensional model for the Cherenkov laser is considered which is composed of a planar relativistic electron beam and a parallel plate waveguide, one plate of which is loaded with a dielectric grating. First, the nonlinear characteristics for the growth of the electromagnetic wave are considered for a dielectric grating with constant parameters. The variation of the groove depth or the slot width in a dielectric grating is found to have the same effect on the growth characteristics as the variation of the permittivity of a dielectric sheet with constant thickness. Then, in order to enhance the efficiency in energy transfer from the electron beam to the electromagnetic wave in the Cherenkov laser, one of the grating parameters or the groove depth is adiabatically decreased in accordance with the decrease in the average velocity of the electron beam. The result of numerical simulation shows that sufficient efficiency enhancement in energy transfer is achieved with the use of a dielectric grating with a variable parameter.