4GLS-the UK's fourth generation light source at Daresbury: new prospects in biological surface science

4GLS is a suite of accelerator-based light sources planned to provide state-of-the-art radiation in the low energy photon regime. Superconducting energy recovery linac (ERL) technology will be utilized in combination with a variety of free electron lasers (IR to XUV), undulators and bending magnets. The 4GLS undulators will be optimized to generate spontaneous high flux, high brightness radiation, of variable polarization, from 3 to 100 eV. The ERL technology of 4GLS will allow shorter bunches and higher peak photon fluxes than possible on storage ring sources. It also provides pulse structure flexibility and an effectively infinite beam lifetime. The XUV and VUV free electron lasers will be used to generate short (femtosecond regime) pulses of extreme ultraviolet light that is broadly tunable and more than a million times more intense than the equivalent spontaneous undulator radiation. A strong feature of the scientific programme planned for 4GLS is dynamics experiments in a wide range of fields. Pump-probe experiments will allow the study of chemical reactions and short-lived intermediates on the timescale of bond breaking and bond making, even from very dilute species. The high intensity of the FEL radiation will allow very high resolution in imaging applications, using near-field approaches. For example, in the IR regime, resolution of the order of 30-50 nm should become possible, allowing the sub-cellular structure of live cells to be examined. The combination of high brilliance with short pulse lengths from multiple sources will allow development of techniques that probe the nature of biomolecule interactions with surfaces. These include methods for probing conformational changes on binding such as time-resolved sum-frequency spectroscopy and reflection anisotropy spectroscopy.