Single-Element Broadband VLS Grating Monochromator

Abstract

The concept of a new monochromator based on a plane VLS grating with an exponential dependence of the line frequency on the coordinate, in which the deflection angle is constant, and the slits, source, and radiation detector are fixed, is proposed. Wavelength scanning is carried out using a linear translation of the grating along its surface, while the diffracted radiation remains focused on the exit slit, and aberrations do not increase. The scheme of the device for use on a synchrotron source in the spectral range 125–4200 Å is calculated. The distance from the source to the grating is 28.55 m, the distance from the grating to the exit slit is 650 mm, the constant grazing angle of incidence onto the grating is 7°, and the constant deflection angle is 19.5°. The resolving power is 6000 with an exit slit width of 8 µm. The line frequency varies from ~1300 to ~35 mm^–1. Several interchangeable gratings are expected to cover the full bandwidth. A similar approach turned out to be applicable to the design of a compact (in particular, shorter than one meter) high-resolution monochromator with equal distances from the entrance slit to the VLS grating and the VLS grating to the exit slit. Such a monochromator can be used, for example, in combination with a repetitively pulsed laser-plasma radiation source in the vacuum region of the spectrum.