Laser focusing limitations from nonlinear beam instabilities

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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.