ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
Laser fusion requirements for ignition of thermonuclear fuel include high levels of irradiation uniformity on target. The quality of each beam's focal spot is a major source of the dominant modes of nonuniformity. The problem is proportionately more difficult at the shorter wavelengths required for high energy-to-target coupling efficiency. Phase conversion is a focusing strategy that incorporates several wave-front modulation techniques which, when operating together, cause a reduction in the spatial coherence of the laser and thus an increase in focal uniformity. Phase masks are central to phase conversion by providing a reproducible source of multibeamlet superposition. A second type of wave-front modulation involves the addition of time-dependent phase to the laser beam, thus producing a time-dependent spectrum. Further manipulation of the beam with a diffraction grating creates color cycling over the elements of the phase mask. Another technique of interest utilizes a static, spatially distributed differential phase. This effectively doubles the number of incoherent beams that are available to overlap and better averages the various intensity nonuniformities. These three techniques have been implemented on the OMEGA laser system producing the highest quality short wavelength ICF laser. Various diagnostics are required to ensure that spatial coherence is rapidly reduced. Focal plane measurements of the spatially integrated spectrum, the spatially resolved irradiation pattern and of the one-dimensional, spatially resolved pulse shape are successfully used to understand the time resolved and time integrated uniformity levels for the OMEGA laser. This work was supported by the U.S. Department of Energy Office of Inertial Fusion under agreement No. DE-FC03-85DP40200 and by the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1141622
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