First observation of the $\gamma$-ray beam production by the backward Compton scattering of extreme ultraviolet light emitted from an undulator

TL;DR

This paper reports the first experimental observation of gamma-ray beam production via backward Compton scattering of extreme ultraviolet light from an undulator at a 1 GeV storage ring, demonstrating a novel high-energy gamma-ray source.

Contribution

The study introduces an innovative method using EUV light reflected back into a storage ring to produce gamma rays, achieving higher energies than conventional laser-based methods.

Findings

Gamma-ray beam observed at 0.543 GeV maximum energy.

Production rate of 1.4 kcps above 0.160 GeV.

Theoretical calculations accurately reproduce the measured spectrum.

Abstract

Compton scattering of photons off high-energy electrons is a fundamental quantum mechanical process widely utilized to produce a $\gamma$-ray beam for scientific research. Instead of injecting laser light into a storage ring as a conventional way, we have developed an innovative method to achieve drastically higher energies approaching the ring energy by the backward Compton scattering of extreme ultraviolet light. In this method, $92$ $\mathrm{eV}$ photons obtained from an undulator in a storage ring were reflected back to the original ring using a Mo/Si multilayer mirror. Consequently, $\gamma$-ray beam production through the extreme ultraviolet light Compton scattering was observed for the first time in a demonstration experiment at the $1$ $\mathrm{GeV}$ ring, NewSUBARU. The measured energy spectrum was well reproduced by a theoretical calculation with the maximum energy of $0.543$ $\mathrm{GeV}$. The production rate was $1.4 \pm 0.1$ kcps for the energies above $0.160$ $\mathrm{GeV}$. This rate was quantitatively explained by the luminosity and the scattering cross section. The present work paved the way to create a new $\gamma$-ray beam source for future applications such as hadron photoproduction experiments.