First demonstration of coherent resonant backward diffraction radiation for a quasi-monochromatic terahertz-light source

Norihiro Sei,Toshiharu Takahashi

doi:10.1038/s41598-020-64426-1

Abstract

We proposed coherent resonant backward diffraction radiation (CRBDR), which generates wavelength-tunable quasi-monochromatic lights using a compact diffractor assembly in an accelerator facility of high-energy electron beams, as a unique intense terahertz (THz) light source. Superimposing the coherent backward diffracted radiation emitted by periodically arranged hollow diffractors, it is possible to amplify the frequency components satisfying a resonant condition, and make the radiation monochromatic. We demonstrated the CRBDR using the L-band linac at the Institute for Integrated Radiation and Nuclear Science at Kyoto University. It was observed that the coherent backward diffraction radiation was amplified more than three times at a frequency which was the fundamental resonant frequency in the CRBDR theory. Moreover, the number of diffractors at the saturation of the radiation power was consistent with the number estimated from the electron distribution in a bunch. The experimental results show that the CRBDR is useful as a quasi-monochromatic light source in the THz band.

Highlights

We proposed coherent resonant backward diffraction radiation (CRBDR), which generates wavelengthtunable quasi-monochromatic lights using a compact diffractor assembly in an accelerator facility of high-energy electron beams, as a unique intense terahertz (THz) light source
We provided a basic theory for this coherent resonant backward diffraction radiation (CRBDR), and report the results of the demonstration experiments conducted at the Institute for Integrated Radiation and Nuclear Science at Kyoto University (KURNS-LINAC)
When the intensity of the coherent backward diffraction radiation (CBDR) is low in the attenuation phase, the intensity of the multiple CBDR becomes lower in the attenuation phase and it is difficult to accurately evaluate the amplification factor

Summary

Introduction

We proposed coherent resonant backward diffraction radiation (CRBDR), which generates wavelengthtunable quasi-monochromatic lights using a compact diffractor assembly in an accelerator facility of high-energy electron beams, as a unique intense terahertz (THz) light source. To facilitate simultaneous usage of THz lights with other accelerator-based quantum sources, the development of a tunable high-power light source in the THz band, by inserting a small device into the existing electron beam trajectory, is desired. Smith-Purcell backward wave oscillator using a metal diffraction grating has been developed as a powerful monochromatic light source in the THz band[17,18]. A high-power quasi-monochromatic beam in the THz band can be expected by superimposing multiple coherent diffraction radiations.

Methods

Results

Conclusion