An Undulator Facility for Precision Optical Testing

The development of reflective optics for projection soft x-ray lithography will require new tools, previously available only at longer wavelengths. Among these is a test facility for large numerical aperture interferometry at short wavelengths. As with visible light interferometry this is most effectively done with coherent radiation. In this paper we discuss the spatial and temporal coherence properties of undulator radiation, wavelength tuning range, design tradeoffs involving harmonic content and thermal loading, and challenges associated with at-wavelength interferometry of complex surfaces. Preliminary plans for such a facility at Berkeley's Advanced Light Source will be discussed. This work is supported by DARPA, AFOSR, and DOE/BES.