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Applied Optics

Applied Optics


  • Vol. 44, Iss. 14 — May. 10, 2005
  • pp: 2805–2817

Near-field nonuniformities in angularly multiplexed KrF fusion lasers with induced spatial incoherence

Robert H. Lehmberg and Yung Chan  »View Author Affiliations

Applied Optics, Vol. 44, Issue 14, pp. 2805-2817 (2005)

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Induced spatial incoherence (ISI) has been proposed for KrF laser drivers to achieve the high degree of spatial beam uniformity required for direct-drive inertial confinement fusion. Although ISI provides ultrasmooth illumination at the far field of the laser, where the target is located, it can still allow the beams in the quasi–near field to develop a time-averaged spatial structure. This speckle, which arises primarily from random-phase aberration, builds up as the laser beams propagate away from the pupil plane located at the final amplifier stage; it is distinct from any structure imposed by gain nonuniformities in the amplifiers. Because of the spatial incoherence, the speckle is significantly smaller than that experienced by coherent beams. Nevertheless, it remains a damage issue, especially for the long beam delay paths required in angularly multiplexed KrF lasers. We develop a novel algorithm for calculating the time-integrated intensities; compare simulations and measurements of the near-field speckle in the Nike KrF laser; and explore options, such as aberration reduction and optical relaying, for controlling the problem in future angularly multiplexed KrF drivers.

© 2005 Optical Society of America

OCIS Codes
(030.6140) Coherence and statistical optics : Speckle
(030.6600) Coherence and statistical optics : Statistical optics
(070.2590) Fourier optics and signal processing : ABCD transforms
(140.2180) Lasers and laser optics : Excimer lasers
(350.2660) Other areas of optics : Fusion
(350.5500) Other areas of optics : Propagation

Original Manuscript: May 13, 2004
Revised Manuscript: November 8, 2004
Manuscript Accepted: November 10, 2004
Published: May 10, 2005

Robert H. Lehmberg and Yung Chan, "Near-field nonuniformities in angularly multiplexed KrF fusion lasers with induced spatial incoherence," Appl. Opt. 44, 2805-2817 (2005)

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