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Development of a Silicon-Based Electron Beam Transmission Window for Use in a KrF Excimer Laser System

C. A. Gentile, H. M. Fan, J. W. Hartfield, R. J. Hawryluk, F. Hegeler, P. J. Heitzenroeder, C. H. Jun, L. P. Ku, P. H. LaMarche, M. C. Myers, J. J. Parker, R. F. Parsells, M. Payen, S. Raftopoulos, J. D. Sethian

Fusion Science and Technology / Volume 43 / Number 3 / May 2003 / Pages 414-419

Technical Paper / Lasers and Heavy-Ion Drivers

Princeton Plasma Physics Laboratory, in collaboration with the Naval Research Laboratory, is currently investigating various novel materials (single-crystal silicon, <100>, <110>, and <111>) for use as electron beam transmission windows in a krypton fluoride (KrF) excimer laser system. The primary function of the window is to isolate the active medium (excimer gas) from the excitation mechanism (field-emission diodes). The chosen window geometry must accommodate electron energy transfer >80% (750 keV) while maintaining the structural integrity during the mechanical load (1.3- to 2.0-atm base pressure differential, ~0.5-atm cyclic pressure amplitude, 5-Hz repetition rate) and the thermal load across the entire hibachi area (~0.9 Wcm-2). In addition, the window must be chemically resistant to attack by fluorine free radicals (hydrofluoric acid, secondary). In accordance with these structural, functional, and operational parameters, a 22.4-mm square silicon prototype window, coated with 500-nm thin-film silicon nitride (Si3N4), has been fabricated. The window consists of 81 square panes 0.019 ± 0.001 mm thick. The stiffened (orthogonal) sections are 0.065 mm wide and 0.500 mm thick (approximate). Assessment of silicon (and silicon nitride) material properties and computer-aided design modeling/analysis of the window design suggest that silicon may be a viable solution to inherent parameters and constraints.

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