High peak power THz source for ultrafast electron diffraction

Shengguang Liu

doi:10.1063/1.5013317

Abstract

Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a device setup to carry out ultrafast fundamental research. A photocathode RF gun generates electron bunches with ∼MeV energy, ∼ps bunch width and about 25pC charge. The electron bunches inject the designed wiggler, the coherent radiation at THz spectrum emits from these bunches and increases rapidly until the saturation at ∼MW within a short wiggler. THz pulses can be used as pump to stimulate an ultra-short excitation in some kind of sample. Those electron bunches out of wiggler can be handled into bunches with ∼1pC change, small beam spot and energy spread to be probe. Because the pump and probe comes from the same electron source, synchronization between pump and probe is inherent. The whole facility can be compacted on a tabletop.

Highlights

Terahertz radiation is electromagnetic wave in the frequency interval from 0.1 THz to 10 THz, which once was an electromagnetic spectrum “gap” between radiofrequency wave and optical wave due to the lack of radiation sources
We focus our attentions on accelerator-based sources of THz radiation
The photocathode RF gun driven by the ultrafast laser pulses can generate electron bunches with high peak current and much short than THz wavelength

Summary

INTRODUCTION

Terahertz radiation is electromagnetic wave in the frequency interval from 0.1 THz to 10 THz, which once was an electromagnetic spectrum “gap” between radiofrequency wave and optical wave due to the lack of radiation sources. THz radiation base Free Electron Laser mechanism (THz-FEL) is a good pump tool for fundamental science, with favorable properties, high peak power, short pulse, and tunable wavelength. The electron bunch is much shorter than the radiation wavelength, we can get significant FEL radiation peak power, Ne is at 108 levels in general case. Some successful applications of intense THz radiation have been done to control materials properties by high THz-fields Such as insulator–metal transitions,[13] orbital order,[14] superconductivity[15] or spin waves[16] can be controlled by the transient electric or magnetic field. THz pulses with high peak power pump some kind of sample to generate resonant excitation and electron bunch probe the sample after an adjustable time delay, and electron diffraction pattern is recorded. The temporal resolution is fundamentally limited by the pulse duration of pump and probe pulses

FACILITY SETUP

THz FEL GENERATION

ULTRAFAST ELECTRON DIFFRACTION WITH PUMP-PROBE TECHNOLOGY

CONCLUSIONS