The long straight section I05 of the Diamond storage ring can accommodate a long period undulator with a sufficient number of periods to give a flux of more than 1015 ph/sec/0.1%BW/100 mA. The undulator is of Apple II type, delivering linear horizontal and vertical and circularly polarised radiation over the full energy range of 18 – 240 eV.
The collimated plane grating monochromator (cPGM) consists of a first, vertically collimating mirror (M1 toroidal), a plane mirror and a plane diffraction grating. One of two cylindrical mirrors (M3 and M6) will focus the beam onto a precision exit slit in either the HR-ARPES or the Nano-branch. The cPGM of I05 has an entrance leg of 26 m (source to M1), two choices of gratings (400 l/mm and 800 l/mm) and an exit leg of 11 m (focusing mirror to exit slit; 6 m for the nano-branch). It can achieve an energy resolving power of up to E/ΔE > 20,000 resulting in an energy resolution of better than 2 meV in the core range of 18 – 80 eV in the HR-ARPES branch. In the nano branch a relaxed energy resolution down to E/ΔE = 3000 is used in the photon energy range of 50 – 200 eV to benefit from the higher transmission.
The first mirror (M1 toroidal) forms an intermediate horizontal image of the source 6 m after the focusing mirror (M3 cylindrical). A vertical intermediate image is formed on the exit slit 11 m after the focussing mirror. These intermediate images are re-focused onto the sample resulting in a beam spot of about 50x50 μm2.
The nano-focussing system is seen in the drawing above. A Fresnel zone plate with order sorting aperture forms a highly de-magnified image of the exit slit on the sample. The beam is deflected by a plane mirror M7. In the same position as the plane mirror, a toroidal mirror M8 can be inserted and the zone plate removed to form a larger beam spot on the sample for characterisation studies prior to small spot microscopy.
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