Speaker
Description
In gamma-ray astronomy, detectors with high sensitivity in the MeV region, which have not yet been explored, are expected to be flown in space in the future [1]. In UVSOR synchrotron facility at Institute for Molecular Science, a MeV gamma-ray pulse source has been developed for user applications such as positron annihilation spectroscopy [2] and gamma-ray detector evaluation. Gamma rays with a maximum energy of 6.6 MeV are generated by 90-degree inverse Compton scattering (ICS) between a 750 MeV electron beam and a Ti:Sa laser with a wavelength of 800 nm [3]. The calculated pulse width of the gamma rays is 5 ps, with a repetition rate of 1 kHz and an estimated intensity of 300 photons/pulse. The gamma-ray energy can be varied down to 3 MeV by selecting the gamma-ray scattering angle as it varies with the position of the beam cross section. The gamma rays possess other characteristics such as quasi-monochromatic (dE/E = a few %), highly polarized (~100%), and low divergence angle (<1 mrad). Linearly polarized gamma rays are generated by scattering of a linearly polarized laser and electron beam, and their polarization axis can be tuned to any angle by changing the angle of a half waveplate. Moreover, circularly polarized gamma rays can be generated using a circularly polarized laser, and their helicity can be easily inverted. The highly polarized and energy tunable gamma-ray sources are ideal as a light source for measurements of directional sensitivity, polarization, and energy for astronomical gamma-ray detectors. ICS gamma rays are available at UVSOR as well as at SSRF in Shanghai, Duke University, and NewSUBARU.
In this conference, details of the UVSOR’s gamma-ray source, including energy tunability, energy spread, and polarization characteristics, will be presented. The most basic polarization property of ICS gamma rays is that the polarization of linearly and circularly polarized gamma rays varies with the position of the beam cross section. The results of polarization measurements using a Compton polarimeter are described [4]. In addition, the spatial intensity distribution [5] and polarization characteristics of gamma rays generated by lasers with axially symmetric polarization states such as radial and azimuthal polarization, which have not been investigated theoretically or experimentally, will also be presented.
[1] C. Ilie, Pub. Astro. Soc. Pac., 131 (2019) 111001.
[2] Y. Taira et al., Rev. Sci. Instr., 93 (2022) 113304.
[3] Y. Taira et al., Nucl. Instr. Meth. A, 652 (2011) 696.
[4] Y. Taira et al., Phys. Rev. A, 107 (2023) 063503.
[5] Y. Taira, Phys. Rev. A, 110 (2024) 043525.
