Critical Wavelength in the Metal Waveguide Partially Filled with Nonlinear Crystal

The bandwidth in the system of the nonlinear optical crystal partially filling the cross-section of a rectangular metal waveguide is investigated. Partial filling of a metal waveguide with a nonlinear optical crystal is used to ensure the phase matching for an effective generation of THz radiation in a nonlinear crystal when it is illuminated with the femtosecond optical laser pulse. The critical wavelengths of a metal waveguide with a central symmetric arrangement of crystal plates in the waveguide are numerically calculated depending on the degree of partial filling and the dielectric permittivity of the crystal. It is shown that partial filling of the waveguide with crystal results in an expansion of the bandwidth of the fundamental mode of the odd type Н₁₀, without improving the propagation conditions for the nearest higher even mode Н₂₀, but on the contrary, at a certain degree of filling with the crystal excludes its occurrence.