A.M.Zabelin.

Using of the invention falls into power laser optics and can be applied in devices of laser beam focusing. Substance: for reducing of aberrations in reflecting focusing lens the reflecting mirror is made from material, transmittant on laser beam wave length with a high index of refraction, while the reflecting coat is applied to back, cooled surface of mirror, and the forward surface of mirror is clarified. The mirror is executed as a cotter between forward flat and back spherical surface with a corner a = q / 2 n. At normal beam incidence on the mirror the cotter is received for 0, and curvature radiuses of forward and back surfaces of mirrors have ratio R1/R2=n.