Design of a High Flux Vacuum-Ultraviolet Beamline for Circular Dichroism Experiments

Abstract

A vacuum‐ultraviolet bending‐magnet beamline for circular dichroism (CD) experiments has been designed. To maximize the photon flux and minimize the focused beam size, a cylindrical mirror and a cylindrical grating with independent optical functions are utilized. The beamline can collect a 30 mrad horizontal by 7 mrad vertical solid angle of synchrotron radiation. By using a 600 grooves/mm grating, the calculated photon flux is greater than 1×1013 photons/sec and the focused beam size is 0.4 mm×0.65 mm for the spectral range from 130 nm to 330 nm with the energy resolving power set at 1000. The linear polarization degree is better than 75% and can be increased to 90% by reducing the vertical acceptance angle down to 2 mrad. In addition to the high flux mode described above, this beamline can also be operated in a high resolution mode. By using a 1200 grooves/mm grating, a resolving power greater than 10,000 can be achieved for the spectral range from 180 to 330 nm. This beamline can provide photon flux as high as the best synchrotron CD beamlines in the world while offers simultaneously a smaller focused beam size.