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

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.

Peak Shift of Coherent Edge Radiation Spectrum Depending on Radio Frequency Field Phase of Accelerator

“…As shown in Figure 6, there is a local maximum of the form factor at a frequency that is away from zero. The coefficient b ∆ in Equation ( 6) was negative in the observed CER spectrum, therefore, the function of the electron distribution in the bunch could not be expressed as in Equation (11). However, by using a pseudo-Voigt function with a negative η, it is possible to reproduce a structure similar to the observed CER spectrum.…”

“…Coherent edge radiation (CER) propagates on the conical surface and can be extracted and used simultaneously with other light sources [9,10]. Recently, a phenomenon whereby the CER intensity was amplified on oscillation of a free-electron laser (FEL) was discovered [11]. It is expected that this phenomenon would elucidate the complete picture of the change of the electron bunch shape due to the FEL interaction by observing the CER.…”

Deformation of an electron bunch caused by free-electron lasers

“…It was observed that the CER power increased with an increase in the FEL. The measured CER spectrum suggested that the FEL caused a backward shift of the distribution of the electrons in the bunch and shortened the root-mean-square (RMS) bunch length [13]. However, in the experiments conducted at LEBRA, the extraction efficiency of the FEL was low, and elongation of the electron bunch was not clearly observed even near the perfect synchronism condition between the electron bunch and the FEL pulse.…”

“…It is significant for non-destructively measurement of the temporal evolution of the electron bunch in the amplification process of the cavity-type linac FEL. A coherent edge radiation (CER) source was developed for electron-bunch length measurements at an infrared FEL facility of the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University [12,13]. By using a perforated mirror that was inserted in front of a downstream cavity mirror for the FEL, a CER beam generated by a downstream bending magnet was extracted from the optical cavity without disturbing the FEL, and its characteristics were measured during the FEL oscillation.…”

Disassembly of Amyloid Fibril with Infrared Free Electron Laser

“…Presently, IR-FELs are open at many synchrotron-radiation facilities all over the world since the optical emission was first observed at a laboratory level more than 50 years ago [ 31 ]. Various original experimental studies using IR-FELs are reported as follows: ablation of biological tissues [ 32 , 33 , 34 ], alteration of biological functions [ 35 , 36 ], degradation of protein–metal complexes [ 37 , 38 ], optical and spectroscopic imaging [ 39 , 40 , 41 ], structural dynamics of biomolecules [ 42 , 43 ], chemical reactions in the gas phase [ 44 , 45 , 46 ], decomposition of biopolymers [ 47 , 48 , 49 ], nonlinear-optical physics [ 50 ], and observation of terahertz radiation [ 51 ].…”