The monochromator operates with a fixed included angle of 160 . To remain in focus at all energies, the exit slits are translated along the optical axis. The length of travel is slightly greater than 100 mm. The monochromatic radiation is focused onto the sample by a toroidal mirror. The resolution terms calculated from the optical path function are shown in the figures below.
Primary coma is the only significant aberration term.
For slit widths greater than 50 m the monochromator is slit width limited over its full range. The resolution of the monochromator, when it is operated with 10 m entrance slits in the high energy range, is shown below. The collection efficiency of such narrow slits is an order of magnitude lower than that of 50 m slits,while the peak resolution improves by a factor of 4. For slit widths greater than 10 m the effect of a 0.2 arc second slope error is not significant. Polarization Polarization is selected by means of a defining aperture, or chopper.