Flat-field VLS spectrometer for a wavelength range of 50–275 Å

A flat-field VLS spectrograph for a wavelength range ~50 – 275 Å with an average linear dispersion of 0.18 mm Å^-1, which makes use of a grazing-incidence varied line-space (VLS) grating, was calculated and implemented (a spectrograph of Harada class). To fabricate the VLS grating by interference lithography technique, an algorithm was developed for calculating the writing configuration with an auxiliary aberrating mirror (the solution of the inverse problem of interference lithography). The spectrograph was put to a test and line spectra were recorded from the laser-produced plasma of lithium fluoride and teflon targets, which were excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm). A resolving power λ/σ λ = 800 was demonstrated in a wavelength region of 135 Å.