Multilayer-coated echelle gratings for soft x rays and extreme ultraviolet

Abstract

Mechanically ruled or ion-etched blazed diffraction gratings can be coated with multilayer reflectors to increase their on-blaze efficiency in the soft x-ray and extreme ultraviolet (EUV) spectral regions. The quality of the groove facets produced by these conventional manufacturing techniques precludes their use in high spectral orders to achieve high resolving power, i.e., as echelles. However, coarse gratings fabricated in crystalline silicon by orientation-dependent etching have excellent groove profile and extremely smooth facets, which make them ideal for coating with multilayers for use as echelles at short wavelengths. Such a grating was coated with tungsten-carbon multilayers for use at soft x-ray wavelengths near the carbon K edge. It was evaluated using both a reflectometer based on a laser-produced plasma source and with synchrotron radiation. In the 50–220 Å wavelength region, diffraction orders up to the 61st were observed, allowing the grating performance to be compared with theoretical predictions. Such multilayer-coated echelles offer the possibility of extremely high spectral resolving power in the EUV and soft x-ray region.