To the best of our knowledge, 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 that combines the functions of a grating and a zone plate is fabricated with Fourier optical techniques and employed here for the first time at EUV/soft-x-ray wavelengths. Both the real and the 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.
© 2002 Optical Society of America
Chang Chang, Erik Anderson, Patrick Naulleau, Eric Gullikson, Kenneth Goldberg, and David Attwood, "Direct measurement of index of refraction in the extreme-ultraviolet wavelength region with a novel interferometer," Opt. Lett. 27, 1028-1030 (2002)