Development and application of soft X-ray multilayer VLS spherical gratings for a flat-field spectrograph

A multilayer laminar-type holographic grating having an average groove density of 2400 lines/mm was designed and fabricated for use with a soft X-ray flat field spectrograph covering the 0.70-0.75 nm region. The varied-line-spaced grooves pattern was generated by use of an aspheric wavefront recording system and the laminar-type grooves were formed by a reactive ion-etching method. Mo/SiO2 multilayers sets of three optimized for the emission bands of hafnium M, silicon K, and tungsten M were deposited on the three sub areas on the grating surface. At the centers of the sub-areas the first-order diffraction efficiencies were 18 - 20% at the respective photon energies. The flat field spectrograph equipped with the grating indicated a spectral line width of 8 - 14 eV for the emission spectra generated by use an electron-impact x-ray source. (author)