ABSTRACT
The basic irradiation uniformity requirements and practical ways of achieving the requirements are both discussed in this chapter, along with two beam-smoothing techniques: induced spatial incoherence and smoothing by spectral dispersion. Because X-ray imaging, and the electron density profile provide indirect measurements of the heat flux, they can be affected by factors other than the rate of heat transport into the ablation region, such as irradiation nonuniformities, radiation transport, or, in the case of neutron yield, Rayleigh-Taylor instabilities. The objective of inertial confinement fusion is to achieve a high gain in the laboratory, of the order of 100 or greater. The stringent requirements for irradiation uniformity demand attention to achieving smooth individual laser beam profiles together with a suitable geometric disposition of a moderate number of beams. Techniques such as static phase correction, adaptive optics, or phase conjugation are either excessively expensive, difficult to implement, or not available at the large apertures and high peak powers required for fusion lasers.
