CD12: a new high-flux beamline for ultraviolet and vacuum-ultraviolet circular dichroism on the SRS, Daresbury.

This paper describes the commissioning and characterization of an SRS bending-magnet beamline constructed for the measurement of vacuum-ultraviolet circular dichroism on biological and other materials. The beamline provides photon fluxes of many orders of magnitude greater than commercial instruments or beamlines at other synchrotron radiation facilities. The beamline uses the conventional approach of utilizing the plane polarized light emitted from the bending magnet which is subsequently converted into circularly polarized light using a photoelastic modulator with a switching frequency of 50 kHz. The beamline has a best wavelength resolution of 0.5 nm and stray light levels better than 0.01%. The latter may be predicted to give improved performance over other beamlines at synchrotron radiation sources especially when short-wavelength CD spectra are to be collected. An example spectrum and submillisecond time-resolved CD profile are given and the impact that the new beamline is likely to have is speculated on. The ultimate flux limitations of the technique with regard to the avoidance of the effects of radiation damage are also discussed.