OPTICAL DESIGN FOR A BENDING-MAGNET BEAMLINE BASED ON A VARIED-LINE-SPACING PLANE GRATING

A vacuum ultraviolet beamline with a grazing-incidence constant-deviat ion-angle monochromator, equipped with varied-line-spacing plane grati ng, has been designed for a bending-magnet light source. This type of monochromator has become very popular because of its high resolution, high throughput, simple scanning mechanism and fixed exit slit. To imp rove the energy resolution for a wide spectral range, Yan & Yagishita [(1995), KEK Report 95-9. KEK, Tsukuba, Ibaraki 305, Japan] proposed e liminating the defocus aberration at two specific energies in the spec tral range, and their monochromator successfully achieved higher energ y resolution by using an undulator light source. The possibility of ap plying this method to a bending-magnet beamline was examined and it wa s found that high performance can be achieved even using a bending-mag net light source with wide emittance. Performance evaluation relating to energy resolution, photon flux and spot size are reported.