| AVS 54th International Symposium | |
| Vacuum Technology | Thursday Sessions |
| Session VT2-ThA |
| Session: | Large Vacuum Systems |
| Presenter: | B. Ashe, University of Rochester |
| Authors: | B. Ashe, University of Rochester K.L. Marshall, University of Rochester D. Mastrosimone, University of Rochester C. McAtee, University of Rochester |
| Correspondent: | Click to Email |
The University of Rochester's Laboratory for Laser Energetics is in the final stages of constructing the OMEGA EP short-pulse, petawatt laser system. A critical component for OMEGA EP is the grating compressor chamber (GCC). This large (12,375-ft3) vacuum chamber contains critical optics where laser-pulse compression is performed at the output of the system on two 40-cm-square-aperture, IR (1054-nm) laser beams. Critical to this compression, within the GCC, are four sets of tiled multilayer-dielectric (MLD) diffraction gratings that provide the capability for producing 2.6-kJ output IR energy per beam at 10 ps. The primary requirements for these large-aperture (43-cm x 47-cm) gratings are high diffraction efficiency greater than 95%, peak-to-valley wavefront quality of less than @lamda@/10 waves, and high laser-induced-damage threshold greater than 2.7 J/cm2 at 10-ps measured beam normal. Degradation of the grating laser-damage threshold due to adsorption of contaminants must be prevented to maintain system performance. The presence of extrinsic contaminants (either particulate or molecular) in the vacuum system puts the MLD gratings at risk with respect to lowered damage threshold. A number of protocols have been developed and implemented at LLE to minimize MLD grating contamination and characterize the performance of the GCC vacuum chamber. In this paper, we describe the GCC vacuum chamber and component cleaning procedures, the qualification, testing methods, and studies undertaken for materials intended for use within the chamber, the use of absorptive getters to protect the gratings from molecular contamination, and the protocols necessary for the integration and operation of the MLD gratings. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article. Key words: laser-pulse compression, vacuum chamber, cleaning, particulate contamination, molecular contamination.