Long-Term Positioning

High-Precision at 10-7 hPa

The ADvanced RESonant Spectroscopy (ADRESS) beamline at the Swiss Light Source (SLS) is a high-performance soft-X-ray undulator beamline operating in the energy range from 300 eV to 1.6 keV. Its RIXS endstation, for Resonant Inelastic X-ray Scattering, is based on SAXES, a high resolution spectrometer for soft X-rays in the 400 to 1600 eV energy range, jointly developed by the Paul Scherrer Institute and the Politecnico di Milano.

The experimental setup uses a VLS (variable line spacing) grating which can be angularly re-positioned to minimize a deterioration of the spectral linewidth by higher order optical aberrations when operating at more than one energy. For this task, a system was designed to move and position the grating in several degrees of freedom: pitch for changing angle, rolling, vertical positioning, and horizontal transverse movement to allow the use of a second, selectable grating.

For this task of long-term positioning a high accuracy of motion was demanded: Z alignment 32 mm and crystal selection 155 mm with 1 μm resolution each, angular motion over ±5 degrees with a resolution of 20 μrad. Additionally, the whole system needs to be stable over long terms in a vacuum environment of 10-7 hPa.