基于相对论超短电子束的THz源

THz source based on the relativistic ultrashort electron beams

THz波的产生有多种途径,清华大学加速器实验室正致力于发展基于相对论电子束的高峰值功率的THz辐射源。本文分别从高峰值流强的单束团与基于激光整形的多脉冲束团序列出发,介绍实验室在宽谱高电场梯度和准单频可调谐THz辐射等方面的研究进展。高亮度电子束团由新一代光阴极电子枪产生,经3 m行波加速管加速,能量可达~50 MeV,采用速度压缩机制可使束团长度达到百飞秒量级。该超短相对论束团可通过多种机制产生高峰值功率的THz辐射,目前,实验室已通过相干渡越辐射(CTR)获得单脉冲能量18μJ的THz辐射输出。同时,提出了一种结合欠压缩工作模式和漂移压缩方法的新束团压缩方案,可进一步将束团压缩至几十飞秒,有望获得频率范围为0.1 THz^30 THz的超宽谱THz辐射。本文同时介绍了多脉冲超短电子束序列的束团测量实验结果,通过模拟研究验证了基于该束团序列CTR产生高功率、可调谐准单频THz辐射的可行性,并进行了相应的实验方案设计。

THz radiation can be generated in many ways. Tsinghua University Accelerator Laboratory is committed to the development of high peak power THz radiation sources based on the relativistic electron bunches. This paper introduces the broadband THz radiation with high-gradient electric field based on single electron bunch of high peak current, and the tunable single-frequency THz radiation based on bunch train. The electron bunches are generated from the photocathode RF gun, and are accelerated to -50 MeV after a 3 m SLAC type TW accelerating tube. Bunches are compressed to sub-picosecond by velocity bunching scheme and then used to generate intense THz pulses through Coherent Transition Radiation （CTR）. Recently, experimental results have shown that the energy of CTR THz is up to 18 μJ per pulse. Besides, a new velocity bunching scheme is proposed by combining under-compression mode and drift compression, which is a promising way to further compress the electron bunch to tens of femtoseconds and to obtain ultra-broadband THz radiation ranging from 0.1 THz to 30 THz. The experimental results of electron bunch train are also introduced. Simulation results have verified the feasibility of generating tunable narrow-band THz radiation with short bunch train, and the related experiments are designed.