Abstract

Direct-drive inertial Confinement fusion (TCF) requires extremely uniform beams to suppress unwanted hydrodynamic and plasma instabilities. Uniform beams are generated by using random phase plates (RPP)¹ to convert long wavelength inhomogeneities into small scale length speckle and by smoothing out the speckle by rapidly moving it in time using spectral bandwidth and dispersion.² RPPs were developed at the University of Osaka¹ and are now routinely used in many of the ICF facilities worldwide._1,3 We have implemented beam smoothing on one arm of the Nova beam for investigating the growth of Rayleigh-Taylor instabilities in a directly driven target⁵ This consisted of using large aperture, bi-level RPPs for producing a fine-scale speckle pattern, an optical wedge array to further broaden the overall far-field spot, and te1nporally smoothing the speckle pattern using smoothing by spectral dispersion. The phase plates used in these experiments were produced by large scale photolithographic and vapor deposition techniques.⁶

© 1992 Optical Society of America