Nanospectroscopy Beamline Description

The beamline monochromator uses the Variable Line Space (VLS) plane grating architecture. In this way, a large energy range can be covered with a relatively small change in the resolving power. Only two gratings are used to cover the energy range from 50 eV to 1000 eV. This is achieved by coupling the rotation angle of the grating with that of the preceding plain mirror. The first grating has 200 lines/mm and covers the energy range from 50 to 250 eV, while the second grating (400 lines/mm) covers the range from 200 to 1000 eV. The calculated resolving power for the two VLS plane gratings is reported on the left hand panel of the figure. The full line is for the 200 lines/mm grating and the dotted one for the 400 lines/mm grating. The graph shows the measured spectrum of the nitrogen 1s to 1π* absorption from which we deduce a resolving power of 4000 at 400.8 eV, in agreement with the calculations.

The monochromator has been recently upgraded to solve long term stability issues and improve mechanical and optical operation. Our tests demonstrate that the instrument is now extremely stable. A report on the instrument performance is available here.