One of the key requirements for direct-drive laser fusion is a laser whose focal profile is sufficiently smooth and controllable to produce highly symmetric implosions. To achieve this, the NIKE laser will implement the echelon-free ISI technique, in which the desired focal profile is formed at the output of a spatially and temporally incoherent oscillator, then imaged through the laser amplifiers onto the target. Because the amplifiers are located in the quasi far- field of the oscillator, their large scalelength gain and phase nonuniformities will have little effect on the image as long as the light remains highly incoherent. However, small scalelength phase aberrations and nonlinear optical processes must be minimized to maintain good control over the image. After a brief description of the NIKE system, this paper reports on numerical simulations and measurements of profile distortion due to random amplitude and phase nonuniformities, nonlinear refraction, and self-seeded stimulated rotational Raman scattering, and describes the steps being taken to control these effects.