Simplified Modeling of Gradient Fragmented Metal Gratings of the Terahertz Range

The results of the investigation of gradient fragmented gratings in the terahertz range are presented. Numerical calculations of the electric field phase are carried out for waves reflected and transmitted by gradient grating. Field phase profiles are obtained for plane polarization cases with different directions of the electric field vector. Rotation of the polarization plane results in distortion of the phase fronts of the reflected and transmitted waves. The effect of the substrate on which the grating is located on the spatial distribution of the field phase is shown. The curvature of the phase front is similar to the schematic with a concave mirrors for reflected waves and a focusing lens for transmitted waves. Therefore a flat gradient structure acquires the functions of a concave or convex mirror and simultaneously a focusing or scattering lens. Such gradient gratings can be used in various devices, and in particular in resonators of terahertz lasers.