Applying of the flat circular metal gratings as spherical output mirrors of terahertz lasers

Using of the flat circular metal gratings as the concave and convex output mirrors in the resonators of terahertz lasers is proposed. These mirrors allow to obtain a predetermined configuration of the phase wave front upon reflection from a flat circular metal gratings. The phase shift of the reflected wave depends on the grating parameters, in particular such as the width of the bands and the distance between them.