Polarimetry of short-pulse gamma rays produced through inverse compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse [Formula presented] rays based on the fact that [Formula presented] rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original [Formula presented] rays. Polarized, short-pulse [Formula presented] rays of [Formula presented] with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse [Formula presented] rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the [Formula presented]-ray intensity is in good agreement with the simulated value of [Formula presented]. Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be [Formula presented], which is also consistent with the expected value of 1.3%.