High Energy Gamma Ray Beams from Compton Backscattered Laser Light

Collisions of light photons with relativistic electrons have previously been used to produce polarized γ-ray beams with modest (~10%) resolution, but relatively low intensity. In contrast, the LEGS project (Laser+Electron Gamma Source) at Brookhaven will produce a very high flux (>2×10⁷ s^-1) of background-free polarized γ rays whose energy will be determined to a high accuracy (ΔE =2.3 MeV). Initially, 300(420) MeV γ rays will be produced by backscattering UV light from the new 2.5(3.0) GeV X-ray storage ring of the National Synchrotron Light Source (NSLS). The LEGS facility will operate as one of many passive users of the NSLS. In a later stage of the project, a Free Electron Laser is expected to extend the γ-ray energy up to 700 MeV.