Modelling of output mirrors based on circular gradient structures for THz lasers

We substantiate the use of gradient periodic structures placed on a plane substrate and consisting of concentric metal rings with parameters varying in radial direction, as output mirrors for THz lasers. Using computer simulation, it is shown that, with a certain change in parameters, such a structure has the properties of a concave mirror and a focusing lens, which is of importance for output mirrors of THz lasers.