Background reduction in FEL-generated γ-ray beam experiments using giant high-peak power pulses

A new method to eliminate beam-uncorrelated background in photonuclear experiments has been developed at the, High Intensity Gamma-Ray Source (HIgammaS). Background suppression of over 3 orders-of-magnitude has been achieved by using a gain modulation technique to generate giant high-peak power (GHPP) pulses in the OK-4/ Duke storage ring FEL. the time structure of these laser pulses was tuned so that their duration was similar to 100 mus,,repeated every 50 ms. The associated FEL photons were backscattered from 780 MeV electrons to produce linearly polarized 40 MeV gamma-rays having the same time structure as the FEL pulses. As an initial test of the technique, a nearly background-free measurement of the analyzing power in the Compton scattering reaction O-16((γ) over right arrow,gamma)O-16 was performed. (C) 2003 Elsevier B.V. All rights reserved.