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.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
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