4GLS—the UK’s fourth generation light source at Daresbury: new prospects in biologicalsurface science

Abstract

4GLS is a suite of accelerator-based light sources planned to provide state-of-the-artradiation 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 toXUV), undulators and bending magnets. The 4GLS undulators will be optimized togenerate spontaneous high flux, high brightness radiation, of variable polarization, from 3to 100 eV. The ERL technology of 4GLS will allow shorter bunches and higherpeak photon fluxes than possible on storage ring sources. It also provides pulsestructure flexibility and an effectively infinite beam lifetime. The XUV and VUV freeelectron lasers will be used to generate short (femtosecond regime) pulses of extremeultraviolet light that is broadly tunable and more than a million times more intensethan the equivalent spontaneous undulator radiation. A strong feature of thescientific programme planned for 4GLS is dynamics experiments in a wide range offields. Pump–probe experiments will allow the study of chemical reactions andshort-lived intermediates on the timescale of bond breaking and bond making,even from very dilute species. The high intensity of the FEL radiation will allowvery high resolution in imaging applications, using near-field approaches. Forexample, in the IR regime, resolution of the order of 30–50 nm should becomepossible, allowing the sub-cellular structure of live cells to be examined. Thecombination of high brilliance with short pulse lengths from multiple sources willallow development of techniques that probe the nature of biomolecule interactionswith surfaces. These include methods for probing conformational changes onbinding such as time-resolved sum-frequency spectroscopy and reflection anisotropyspectroscopy.