Observation of terahertz coherent edge radiation amplified by infrared free-electron laser oscillations

Norihiro Sei,Yoske Sumitomo,Takeshi Sakai,Yasushi Hayakawa,Ken Hayakawa,Toshinari Tanaka,Kyoko Nogami

doi:10.1038/s41598-021-82898-7

Norihiro Sei, Yoske Sumitomo + Show 5 more

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https://doi.org/10.1038/s41598-021-82898-7

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Abstract

A coupling device, which can extract coherent edge radiation (CER) from an optical cavity for a free-electron laser (FEL) without damaging the FEL due to diffraction loss, was developed at Nihon University. We successfully observed the CER beam with a power of 1 mW or more in the terahertz range during FEL oscillation. It is revealed that the CER power changed with the detuning of the optical cavity and the dependence of the CER power on the detuning length differs from that of the FEL power. The measured CER spectra indicate that the longitudinal electron distribution in a bunch is modulated by the FEL oscillation with a period corresponding to the FEL slippage length. We herein report the characteristics of the CER with FEL oscillation in detail. These results demonstrate that the CER is excellent tool to reveal the overall effect of FEL interaction on electron distribution in a bunch.

Highlights

A coupling device, which can extract coherent edge radiation (CER) from an optical cavity for a free-electron laser (FEL) without damaging the Free-electron lasers (FELs) due to diffraction loss, was developed at Nihon University
We developed a system for observing the CER generated by an electron beam immediately after an FEL interaction at the Laboratory for Electron Beam Research and Application (LEBRA)
By arranging a hollow mirror in the optical cavity, a CER beam with a total power of 30% or more can be extracted during the FEL oscillation without causing a diffraction loss in the FEL

Summary

Introduction

A coupling device, which can extract coherent edge radiation (CER) from an optical cavity for a free-electron laser (FEL) without damaging the FEL due to diffraction loss, was developed at Nihon University. We report the characteristics of the CER with FEL oscillation in detail These results demonstrate that the CER is excellent tool to reveal the overall effect of FEL interaction on electron distribution in a bunch. A technique for observing the bunch length during FEL oscillations is desired to reveal the FEL interaction and to control lasing stably. We observed the coherent edge radiation (CER) emitted in an FEL straight section and measured the bunch shape of the electron beam immediately after an FEL interaction at the infrared FEL facility of the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon U niversity[8]. The experimental results for the change in the CER caused by FEL oscillations are reported for the first time

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