Abstract-Efficient manipulations of circularly polarized terahertz waves with transmissive metasurfaces

Min Jia, Zhuo Wang, Heting Li, Xinke Wang, Weijie Luo, Shulin Sun, Yan Zhang, Qiong He, Lei Zhou,

Fig. 1: Working principle of the high-efficiency photonic spin Hall effect (PSHE) and background-free Bessel beam (BB) generation for circularly polarized (CP) waves in a transmission geometry.

https://www.nature.com/articles/s41377-019-0127-0

The unrestricted control of circularly polarized (CP) terahertz (THz) waves is important in science and applications, but conventional THz devices suffer from issues of bulky size and low efficiency. Although Pancharatnam–Berry (PB) metasurfaces have shown strong capabilities to control CP waves, transmission-mode PB devices realized in the THz regime are less efficient, limiting their applications in practice. Here, based on Jones matrix analysis, we design a tri-layer structure (thickness of ~λ/5) and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom (relative efficiency of ~90%) to build PB metadevices for manipulating CP THz waves. Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system. The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%, whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam. All the experimental results are in excellent agreement with full-wave simulations. Our results pave the way to freely manipulate CP THz beams, laying a solid basis for future applications such as biomolecular control and THz signal transportation.

Abstract-Design of a Pre-Bunched THz Free Electron Laser

Ruixuan Huang, Weiwei Li,  Zhouyu Zhao, Heting Li, Jigang Wang, Tian Ma, Qiuping Huang, Zhigang He, Qika Jia, Lin Wang, Yalin Lu

https://www.mdpi.com/2571-712X/1/1/21/htm

Terahertz (THz) radiation has attracted much attention in new scientific and industrial applications. There has been significant recent progress in generating THz with accelerators. To investigate the collective behavior of electron dynamics, we have proposed a new high throughput material characterization system, which supplies a multiple light source. The system includes a pre-bunched THz free electron laser (FEL), which is a high-power narrow-band THz source with a wide tuning range of frequency. The physical design with the main components of the facility is introduced, and the simulation results are illustrated. Radiation of 0.5–3.0 THz is obtained by the fundamental wave of the pre-bunched beam, and radiation covering 3.0–5.0 THz is realized by second harmonic generation. As the simulation shows, intense THz radiation could be achieved in a frequency from 0.5–5.0 THz, with a peak power of several megawatts (MWs) and a bandwidth of a few percent.

Abstract-Vector measurement and performance tuning of a terahertz bottle beam

Heting Li, Xinke Wang, Sen Wang, Wenfeng Sun, Jiasheng Ye, Peng Han, Shengfei Feng, Yue Yu,  Yan Zhang,

https://www.nature.com/articles/s41598-018-31250-7

A terahertz (THz) bottle beam is realized by adopting the combination of a Teflon axicon and a silicon lens. By using a THz imaging system with a focal-plane array, the vector characteristics of the THz bottle beam are coherently measured and detailedly analyzed, including the transverse (Ex) and longitudinal (Ez) components. The experimental phenomena vividly reveal the distribution characteristics and the formation origin of the THz optical barrier. A vectorial diffraction integral algorithm of a focusing optical system are utilized to exactly simulate the measured results. Besides, the features of the THz bottle beam are effectively tuned by varying the parameters of the Teflon axicon and the silicon lens. This work gives a full view to understand the evolution characteristics of the THz bottle beam and provide a solid experimental foundation for guiding the future applications of this type of THz beam.