San Diego, California, 17-19 June 2002

Development of a Silicon Based Electron Beam Window For Use In a KrF Laser System

C. A. Gentile¹, H. M. Fan¹, R. J. Hawryluk¹, F. Hegeler², P. Heitzenroeder¹,

C. Jun¹, L. P. Ku¹, P. LaMarche¹, J. J. Parker¹, S. Raftopoulos¹, J. D. Sethian³

1. Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543
2. Commonwealth Technology, Inc., 5875 Barclay Dr., Alexandria, VA. 22315
3. Naval Research Laboratory, 4555 Overlook Ave S.W., Washington D.C. 20375

Abstract - Princeton Plasma Physics Laboratory (PPPL), in collaboration with Naval Research Laboratory (NRL), is currently investigating various novel materials for use as electron beam windows in a KrF laser system. One of these materials is crystalline silicon (Si). The purpose of the window is to isolate the lasing medium from the electron beam source. The window dimensions must provide beam energy transfer of >80% (@ 750keV), while maintaining structural integrity during pressure cycling(DP=2atm, ƒ=5Hz) with heat load of 0.9W/cm². In addition, the window must be chemically/physically resistant to attack by fluorine free-radicals. In accordance with these structural, functional, and operational parameters, a silicon wafer, coated with 500nm silicon nitride (SiN₄), has been etched in a fashion that yields a 22.4mm square window. The window consists of 81 square panes with a thickness of 0.019mm ± 0.001mm. The ribbed sections are 0.065mm in width and 0.600mm in height. The following diagram depicts the window configuration.

Silicon, with a maximum fracture strength of 7000MPa¹, is stronger than steel. Preliminary bench top testing has shown that the silicon window can withstand a pressure gradient of 2atm. The window maintains structural integrity when subjected to multiple pressure cycling (@ 5Hz). Electron beam transmission and cooling is actively being investigated. Assessment of silicon (and silicon nitride) material properties and modeling/analysis of the silicon window design suggest that silicon may be a viable solution for KrF laser system parameters and constraints. This paper will detail the work performed in support of employing this novel material for this developmental task.