Undulator
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 will be of Apple II type, delivering linear horizontal and vertical and circularly polarised radiation over the full energy range of 18 – 240 eV.
Monochromator
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 M5) will focus the beam onto a precision exit slit in either the HR-ARPES or the Nano branch. The cPGM of I05 will have 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 9 m (focusing mirror to exit slit; 6 m for the nano-branch). It can achieve an energy resolving power of up to ΔE/E = 40,000 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 ΔE/E = 2000 is used in the photon energy range of 50 – 100 eV to benefit from the higher transmission.
HR-ARPES branch
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.
Nano-branch - conceptual design to be finalised by end 2011
One option of the nano-focussing system is seen in the drawing above. The intermediate image on the exit slit is re-focused onto an intermediate image pin-hole using a micro-focusing mirror with a 1:20 de-magnification. This intermediate image is then de-magnified onto the sample using a nano-focusing element with a 1:50 de-magnification. The choice of nano-focusing elements includes a Fresnel zone-plate, Schwartzschild objectives or K-B mirrors.