System of fibre-optic smoothing of laser radiation on the Luch laser facility

A front end system with spatiotemporal smoothing based on the use of multimode optical fibre has been developed on the Luch laser. The system consists of a broadband master oscillator, a smoothing fibre, preamplifiers, and subsystems for the formation of temporal and spatial radiation profile. The processes of generation of partially coherent radiation, its amplification and conversion into the second harmonic are experimentally investigated. At the amplifying channel output, the pulse energy of the first harmonic reaches up to 1200 J with a pulse duration of 4 ns; the technical coefficient of radiation conversion to the second harmonic is up to 44%, and the beam divergence is 0.2–0.25 mrad. When using smoothed radiation, the speckled structure in the far field is almost completely eliminated: the small-scale inhomogeneity of the target irradiation, integrated over the pulse time, is reduced by 1–2 orders of magnitude compared to unsmoothed radiation.