Laser focusing limitations from nonlinear beam instabilities

Abstract

Compression of fusion targets by irradiation with Nd : glass lasers requires precise focusing of large-aperture high-power laser beams. Nonlinear propagation instabilities cause growth of small-scale amplitude perturbations which reduce the focusing properties of such beams. We present temporal measurements of the focus of a high-power glass laser and we show that the integrated nonlinear phase retardation of the beam (or B value) can be used to determine the maximum focusable energy available from an unspatially filtered amplifier chain.