Abstract-Efficient generation of a high-field terahertz pulse train in bulk lithium niobate crystals by optical rectification

Qili Tian, Hanxun Xu, Yi Wang, Yifan Liang, Yuemei Tan, Xiaonan Ning, Lixin Yan, Yingchao Du, Renkai Li, Jianfei Hua, Wenhui Huang,  Chuanxiang Tang, 

(a) Experimental setup for high-field THz pulse train generation from congruent lithium niobate with TPF technique and EO sampling detection. TFP: thin-film polarizer; BS: beam splitter (50:50); HWP: Half-wave plate; cL: cylindrical lens; cLN: congruent lithium niobate; OAP: off-axis parabolic mirror; BPD: balanced photodiode. (b) The pump laser beam profile in the cLN.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-6-9624&id=449159

 We demonstrate a highly efficient method for the generation of a high-field terahertz (THz) pulse train via optical rectification (OR) in congruent lithium niobate (LN) crystals driven by temporally shaped laser pulses. A narrowband THz pulse has been successfully achieved with sub-percent level conversion efficiency and multi MV/cm peak field at 0.26 THz. For the single-cycle THz generation, we achieved a THz pulse with 373-μJ energy in a LN crystal excited by a 100-mJ laser pulse at room temperature. The conversion efficiency is further improved to 0.77 % pumped by a 20-mJ laser pulse with a smaller pump beam size (6 mm in horizontal and 15 mm in vertical). This method holds great potential for generating mJ-level narrow-band THz pulse trains, which may have a major impact in mJ-scale applications like terahertz-based accelerators and light sources.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Experimental results on the tunable superradiate THz radiation from the undulator in Tsinghua University beamline

Chuanxiang Tang, Wenhui Huang, Xiaolu Su,  Dan Wang, Qili Tian, Yifan Liang,  Lujia Niu, Lixin Yan, Yingchao Du,
http://ieeexplore.ieee.org/document/8067241/

We report the first operation of a widely-tunable 8-period undulator at terahertz (THz) frequencies in the Tsinghua University beamline. We observed the coherent undulator radiation from sub-picosecond electron bunches of 30MeV. The measured radiation curve shows clearly that the radiation energy is proportional to the charge square, and the THz frequency can be changed from 0.4 THz to 10 THz with narrow-band spectrums. Our results demonstrate a high power and tunable coherent THz source, which could be useful for many applications in the future.

Abstract-Phase control with two-beam interferometry method in a terahertz dielectric wakefield accelerator

 Dan Wang, Xiaolu Su, Lixin Yan,   YingChao Du, Qili Tian, Yifan Liang, Lujia Niu,   Wenhui Huang, Wei Gai, Chuanxiang Tang, Sergey Antipov,

http://aip.scitation.org/doi/abs/10.1063/1.4999959

High-gradient, beam-driven wakefield acceleration in THz structures is a promising technology for future free electron lasers and colliders. In this scheme, the main beam is accelerated by the wakefield of the high current drive beam. The time separation between the main and drive beams has to be chosen carefully to ensure that the main beam is in an accelerating phase of the drive's wakefield. THz accelerating structures provide high gradient acceleration due to their small apertures, but their phase control is difficult due to the picosecond-scale period. Here, we report on a wakefield acceleration experiment in a 460 GHz dielectric wakefield accelerator (DWA). The optimum phase of the main beam during the experiment is determined with a two-beam wakefield interferometry (TBI) measurement. This is performed without the measurement of the main and drive beam bunch lengths or their separation. In TBI, the interference of the wakefields produced by the drive and main beams is measured with an integrating THz detector. The TBI signal, as a function of separation between the drive and main beams, exhibits a minimum due to destructive interference of these wakefields, which corresponds to maximum acceleration of the main beam as is confirmed by the energy spectrometer measurement. The maximum energy gain of 0.8 MeV and maximum energy loss of 1.2 MeV for the main beam have been measured, which agrees well with theoretical predictions.

Abstract-Monitoring of electron bunch length by using Terahertz coherent transition radiation

• Xiaolu Su, 
• Lixin Yan, 
• Yingchao Du, 
• Zhen Zhang, 
• Zheng Zhou, 
• Dong Wang, 
• Lianmin Zheng, 
• Qili Tian, 
• Wenhui Huang, 
• Chuanxiang Tang

• Department of Engineering Physics, Tsinghua University, Beijing, China
• Key Laboratory of Particle and Radiation Imaging (Tsinghua University), Ministry of Education, Beijing, China
• 
  

http://www.sciencedirect.com/science/article/pii/S0168583X17302550

In this paper, ultrashort bunch length monitoring was demonstrated based on Terahertz (THz) coherent transition radiation (CTR) in Tsinghua Thomson scattering X-ray (TTX) source. The radiation produced by electron bunch is split into three paths: one of them is used to detect the total energy, while the other two paths are filtered with different THz band-pass filters before detection. The bunch length variation can be obtained by calculating the ratio between the filtered energy and the total energy. The bunch is compressed by a chicane and via changing the current of chicane, the ratio of filtered energy and total energy changed correspondingly. It is a simple supplemental approach to monitor the bunch length during beam conditioning and facility operation. Bunch arrival-time jitter and nonlinear effects in chicane are observed in the experiment during the measurement of filtered energy and total energy.