Abstract

Inertial confinement fusion (ICF) of deuterium-tritium filled capsules with the direct-drive approach requires a high degree of laser radiation uniformity to prevent hydrodynamic instabilities in the imploding target and parametric light scattering instabilities in the coronal plasma. High power ICF laser beams at target typically have an irradiance that exhibits ’hot spots’ many times the average intensity with many large-scale features. Spatially-incoherent broadband laser beams have been used to smooth the irradiance by several techniques, including induced spatial incoherence^[1] (ISI) and smoothing by spectral dispersion^[2] (SSD). Multi-mode fiber-optics have also been used to create spatially incoherent beams which are amplified to high power and directed to target.^[3,4] Generally, the rate of smoothing increases with the bandwidth, and the rms intensity ’noise’ decreases with time to a limit inversely proportional to the square-root of the number of independent speckle fields produced by the smoothing scheme.

© 1992 IQEC