Abstract-Terahertz wavefront manipulating by graphene aperture based metasurface

Pei Ding, Chuang Lv, Li Shao, XiminTian, Yan li. Jinna He


https://www.sciencedirect.com/science/article/pii/S1569441018303377

We propose a kind of gradient metasurface based on graphene apertures for wavefront control of terahertz linear polarized waves. By carefully designing the geometric dimensions of the graphene rectangular apertures, the proposed metasurface can realize arbitrary reflection, carpet cloak and reflective focusing, respectively. The simulation results demonstrate that the cloaking and focusing effects can be actively tuned between ON and OFF state by uniformly tuning the graphene Fermi energy. The metalens based on graphene has high-efficiency, broadband and wide-angle off-axis focusing performance, and the focusing efficiency is significantly dependent on graphene Fermi energy and carrier mobility. When the mobility decreases from 1.0 m2/Vs to 0.1 m2/Vs, the focusing efficiency decreases from more than 70% to about 22% at the operating frequency. The tunable and efficient performance makes the graphene aperture based metasurface have great application potential in ultrathin, lightweight and integrated terahertz devices.

Abstract-Enhancement of THz generation by feedback-optimized wavefront manipulation

J. Hah, W. Jiang, Z-H. He, J. A. Nees, B. Hou, A. G. R. Thomas, and K. Krushelnick

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-15-17271&origin=search

We apply active feedback optimization methods to pyroelectric measurements of a THz signal generated by four wave mixing in air using 1 mJ to 12 mJ, 35 fs laser pulses operating at 12/ kHz$\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\hspace{0.17em}\text{kHz}$repetition rate. A genetic algorithm, using the THz signal as a figure of merit, determines the voltage settings to a deformable mirror and results in up to a 6 fold improvement in the THz signal compared with settings optimized for the best focus. It is possible to optimize for different THz generation processes using this technique.

© 2017 Optical Society of America

Abstract-Terahertz brightness at the extreme: demonstration of 5 GV/m, 17 T low frequency λ3 terahertz bullet

Mostafa Shalaby, Christoph P. Hauri

http://arxiv.org/abs/1407.1656

The brightness of a light source defines its applicability to nonlinear phenomena in science. Bright low frequency terahertz (< 5THz) radiation confined to a diffraction-limited spot size is a present hurdle due to the broad bandwidth and long wavelengths associated with single-cycle terahertz pulses as well as due to the lack of terahertz wavefront correctors. Here, using a present-technology system, we employ a new concept of terahertz wavefront manipulation and focusing optimization. We demonstrate a spatio-temporal confinement of terahertz energy at its physical limits to the least possible 3-dimensional light bullet volume of lambda cubic. This leads to a new regime of extremely bright terahertz radiation reaching 40 PW/m2 intensity. The presented work is focused on the sub-5 THz range using small aperture organic crystals DSTMS and OH1. The obtained peak field of up to 5 GV/m and 17 Tesla is order of magnitude higher than any reported single-cycle field oscillation in the entire THz range from a laser-based system and surpassing large scale accelerator systems. The presented results are foreseen to have a great impact on future nonlinear terahertz applications in different science disciplines.