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Title: SiC Based Laser Fusion Optics

Authors:
 [1];  [1]
  1. Materials & Electrochemical Research (MER) Corporation, Tucson, AZ (United States)
Publication Date:
Research Org.:
Materials & Electrochemical Research (MER) Corporation, Tucson, AZ (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
903506
Report Number(s):
DOE/ER/83279-F
MER #90822 - DE-FG03-01ER83279
DOE Contract Number:
FG03-01ER83279
Type / Phase:
SBIR
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Internal Fusio; SiC Optics; Laser Damage

Citation Formats

Kowbel, Witold, and Withers, James C. SiC Based Laser Fusion Optics. United States: N. p., 2007. Web.
Kowbel, Witold, & Withers, James C. SiC Based Laser Fusion Optics. United States.
Kowbel, Witold, and Withers, James C. Fri . "SiC Based Laser Fusion Optics". United States. doi:.
@article{osti_903506,
title = {SiC Based Laser Fusion Optics},
author = {Kowbel, Witold and Withers, James C.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 18 00:00:00 EDT 2007},
month = {Fri May 18 00:00:00 EDT 2007}
}

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  • A thin film of liquid metal serves as a grazing incident liquid metal mirror (GILMM) for robust final optics of an inertial fusion energy (IFE) power plant. The amount of laser light the mirror can withstand, called the damage limit, of a sodium film 85{degree} from normal arbitrarily set by surface temperature rise of 200 C to limit liquid ablation is 57 J/cm{sup 2} normal to the beam for a 20 ns pulse and 1.3 J/cm{sup 2} for a 10 ps pulse of 0.35 pm light. Liquid aluminum can handle 106 J/cm{sup 2}. The damage limit actually should be setmore » by avoiding liquid ablation due to the rapid surface heating which is expected to result in even higher temperatures rises than 200 C and even higher power densities. The liquid surface is kept flat to the required accuracy by a combination of polished substrate, adaptive optics, surface tension and low Reynolds number, laminar flow in the film. The film's substrate must be polished to {+-}0.015 m. Then surface tension keeps the surface smooth over short distances (<10 mm) and low Reynolds number laminar flow keeps the surface smooth by keeping the film thickness constant to less than {+-} 0.01 pm over long distance >10 mm. Adaptive (deformable) optics techniques keep the substrate flat to within {+-}0.06 {micro}m over 100 mm distance and {+-}0.6 {micro}m over 1,000 mm distances. The mirror can withstand the x-ray pulse when located 30 m away from the microexplosions of nominal yield of 400 MJ (50 MJ x rays) when Li is used but for higher atomic number liquids like Na and Al there may be too high a temperature rise forcing use of other x-ray attenuation methods such as xenon gas, which may be needed for first wall protecting anyway. The cumulative damage from neutrons causing warpage of the liquid film's substrate can be compensated by adaptive optics techniques giving the mirrors long life, perhaps 30 years. The GILMM should be applicable to both direct and indirect drive and pulse lengths appropriate to slow compression ({approximately}20 ns) or fast ignition ({approximately}10 ps). Experiments are discussed to verify the predicted damage limit and required smoothness.« less
  • This program is an assessment of fusion cast polycrystalline calcium fluoride for optical components of 1.064 micrometer pulsed laser fusion systems. Task areas include casting of essentially stress-free 33 centimeter diameter, 5 centimeter thick ingots, developing surface finishing techniques for optically figured plane and spherical surfaces, and evaluate state-of-the-art antireflection coatings deposited onto the specimens of the cast material. During the first quarter, a new casting furnace was installed in the laboratory and put into operation. Two complete casting runs were made. Temperature profiles taken during the first run demonstrated the existence of unacceptably large radial gradients in the furnacemore » and led to the design and installation of new heating elements prior to the second casting effort. Redesigned heating elements and other furnace modifications decreased the radial gradients by more than a factor of three during the second run, but the ingot was still badly strained. Furnace modifications made before a third run, which is now in progress, appear to have further reduced the gradients. Although the upper portion of the ingot from that second run contained growth defects, there is enough sound material to supply substrates for the antireflection coating task. Casting and post-casting annealing treatment studies are continuing.« less
  • This program is an assessment of fusion cast polycrystalline calcium fluoride for optical components of 1.064 micrometer pulsed laser fusion systems. Task areas include casting of essentially stress-free 33 centimeter diameter, 5 centimeter thick ingots, developing surface finishing techniques for optically figured plane and spherical surfaces, and evaluating state-of-the-art antireflection coatings deposited onto specimens of the cast material. During the third quarter, three casting runs were completed in the large casting furnace, none of which was wholly successful. A decision to limit the remainder of the casting effort to six-inch (15-centimeter) diameter pieces was made. Two chemically homogeneous castings ofmore » CaF/sub 2//Nd were made in a second furnace. Diamond abrasive polishing techniques were used successfully to fabricate a 15-centimeter radius convex spherical surface on one polycrystalline casting and a quarter wave plane surface on a second. Both surfaces were free of grain boundary relief which is commonly produced by standard techniques. Antireflection coatings obtained from two vendors were found to be physically durable and optically uniform. The components of these coatings are those also used by the vendors for their laser damage resistant coatings on glass, so it is reasonable to anticipate that they will be damage resistant on the fluoride as well. Damage testing will be carried out during the final quarter of the program.« less