Direct index of refraction measurement at extreme ultraviolet wavelength region with a novel interferometer

The first direct measurement of the dispersive part of the refractive index is performed at extreme ultraviolet (EUV) wavelengths, where absorption is higher as compared with hard x-ray and visible wavelengths. A novel diffractive optical element, which combines the functions of a grating and a zoneplate, is fabricated following Fourier optical techniques and employed here for the first time at EUV/soft x-ray wavelengths. Both the real and imaginary parts of the complex refractive indices are measured directly by this technique without recourse to Kramers-Kronig transformations. Data for Al and Ni, in the vicinity of their L and M-edges, respectively, are presented as first examples of this technique. c ©2001 Optical Society of America