Measurement of the spatial polarization distribution of circularly polarized gamma rays produced by inverse Compton scattering
Y. Taira, Shunsuke Endo, Shiori Kawamura, T. Nambu, M. Okuizumi, T. Shizuma, Mohamed Omer, Heishun Zen, Yasuaki Okano, Masaaki Kitaguchi
Abstract
Inverse Compton scattering of polarized laser photons by energetic electrons is an excellent method to generate polarized gamma rays. A 100% polarized laser can generate 100% polarized gamma rays, but polarization varies depending on the scattering angle of the gamma rays. In this study, we experimentally measure the spatial polarization distribution of circularly polarized gamma rays using a magnetized iron that can measure the circular polarization of MeV gamma rays. Measurements of the asymmetry of gamma-ray transmission relative to the magnetized iron at each scattering angle clearly show that gamma rays are circularly polarized near the central axis, and they change from circular to linear polarization as the scattering angle increases. A simple way to obtain highly polarized gamma rays is to use a collimator that transmits only the central axis of the gamma rays with such polarization characteristics. Polarized gamma rays are, indeed, generated by ${90}^{\ensuremath{\circ}}$ collisional inverse Compton scattering between an electron beam and a circularly polarized laser.