Abstract
Induced spatial incoherence (ISI)1 appears to be a viable technique for achieving the smooth and controllable beam profiles required by direct-drive laser fusion. The spatial incoherence is created by propagating a laser beam of broad spectral bandwidth Δv through a pair of echelon structures that impose a different time delay at each step. If the delay increments Δt are larger than the optical coherence time tc = 1/Δv, the beam is sliced into an array of mutually incoherent square beamlets. Each will focus independently to the same far-field diffraction profile (the sinc2 function) of width f λ/d, provided that its initial width d is small in comparison to the transverse scale length sa of the incident beam aberration. By tilting the alternating eche-ion steps to slightly different aiming angles, one can control the shape of the focal profile, as shown in Fig. 1.
© 1986 Optical Society of America
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