RADIO PHYSICS AND RADIO ASTRONOMY

PACS number: 42.60.By

Purpose: The improvement and development of terahertz radiation sources is required for the further development of the terahertz frequency range. Submillimeter lasers are one of the few sources of terahertz radiation. Metal periodic structures are often used as output mirrors of these lasers. The periodic structure advantage is that by selection of its parameters it is possible to provide the optimal transmittance of the output mirror and the required polarization of laser radiation. The use of concave mirrors in a laser cavity is often required to reduce the diffraction loss and to reduce the output laser beam divergence. However, such mirrors are much more expensive and more complicated in manufacture than the flat ones. The periodic structure with a non-flat substrate is particularly difficult to manufacture. The aim of this work is to study the flat gradient metal gratings that possess the properties of spherical mirrors and lenses simultaneously.

Design/methodology/approach: Flat gradient metal gratings in the form of concentric rings with varying parameters in the radial direction are proposed for solving the focusing problem. The technique for modeling the phase characteristics of such annular gradient gratings is given. Simulation of the properties of a ring grating in which the distance between the rings decreases in the direction from the center to the edges is carried out.

Findings: The image of the change in the wave phase front which occurs when an electromagnetic field interacts with a gradient grating is obtained as a result of numerical simulation. The grating considered has the properties of a concave mirror and a focusing lens simultaneously. Such combination of gradient gratings properties allows to use them as output mirrors of terahertz lasers. This allows us to improve the energy and spatialangular characteristics of the output radiation of terahertz lasers. Сonclusions: Using the circular gradient gratings as output mirrors of terahertz lasers makes it possible to reduce the diffraction losses and divergence of the laser beam that allows to increase the efficiency of terahertz lasers.

Key words: terahertz range, laser, output mirror of a laser cavity, gradient gratings

Manuscript submitted  21.08.2018

Radio phys. radio astron. 2018, 23(4): 302–312

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