CONTROLLABLE SPATIAL INCOHERENCE ECHELON FOR LASER

A system for achieving very uniform illumination of a target. A beam of broadband spatially-coherent light is converted to light with a controlled spatial incoherence and focused on the target. An echelon-like grating breaks the beam up into a large number of differently delayed beamlets with delay increments larger than the coherence time of the beam, and a focusing lens overlaps the beamlets to produce at the target a complicated interference pattern modulated by a smooth envelope that characterizes the diffraction of an individual beamlet. On time scales long compared to the coherence time, the interference pattern averages out, leaving only the smooth diffraction envelope.