Development and applications of soft X-ray multilayer gratings in the keV region

Koike, Masato; Imazono, Takashi; Kawazoe, Tadashi*; Otsu, Motoichi*; Sano, Kazuo*

A Mo/SiO multilayer laminar-type holographic grating having an average groove density of 2400 lines/mm is designed and fabricated for use with a soft X-ray flat field spectrograph. A varied-line-spaced grooves pattern is generated by the use of an aspheric wavefront recording system and laminar-type grooves are formed by a reactive ion-etching method. The measured first-order diffraction efficiency is 1820%. The flat field spectrograph equipped with the grating indicates a spectral line width of 814 eV for the emission spectra generated from electron-impact X-ray sources. A Mo/SiO multilayer grating having a groove density of 7600 lines/mm fabricated by use of a new lithography machine based on optical near field technologies showed first-order diffraction efficiency of 3%. It is over one order magnitude higher than that of the other orders.