Employment of gradient metal-film output mirrors in terahertz discharge lasers - M. I. Dziubenko; S. O. Masalov; Yu. Yu. Kameniev; I. V. Kolienov; V. P. Radionov; M. F. Dakhov; A. I. Puzak; O. I. Dmytruk (Radiophysics and Electronics, 2021)