BeamLine description

GasPhase Photoemission is a high resolution (resolving power 10000 or better) and high flux versatile beam line which covers a wide energy range (13-900 eV) with a stable and almost circular spot size (around 200micron) at the target.

The line is fed by an undulator (U12.5 at exit U6.2, tab. 1), which delivers light in the range from 13.5 eV to well above 900 eV. The monochromator is a Variable Angle Spherical Grating Monochromator, with fixed positions of the slits. The optical design was developed by Sincrotrone Trieste, including a toroidal prefocusing and two refocusing mirrors (spherical and plane-elliptical). The monochromator was commissioned and not only met its specifications (E/ΔE >= 10000) over all the planned working range (13-900 eV) but even exceeded them considerably. A resolving power of 60000 has been measured at 48 eV. It remains higher than 10000 at 540 eV and a value of 8000 is obtained at 860 eV. This resolving power is the highest among the monochromators at ELETTRA. The use of two refocusing mirrors provides a roughly circular spot at the sample (diameter »350micron for a 20 micron exit slit, decreasing to less than 150micron as the photon energy increases above 200 eV). The beamline is connected to the experimental station through a differential pumping section (5 orders of magnitude difference in pressure), to decouple the UHV section of the mirror chambers from the high vacuumin the experimental region.