Abstract-Gate-controlled terahertz focusing based on graphene-loaded metasurface

Naeem Ullah, Weiguang Liu, Guocui Wang, Zongyuan Wang, Ata Ur Rahman Khalid, Bin Hu, Juan Liu, and Yan Zhang

 (a) Schematic of the designed graphene-loaded metalens. A gate voltage Vg is applied to tune the chemical potential of graphene. (b) One unit-cell of the structure under the illumination of a linearly x-polarized THz wave. The transmitted y-polarized wave is dependent on both the C-shaped aperture and the graphene chemical potential. (c) 2-D illustration of a basic unit-cell, where P = 100µm, w = 10µm. The symmetric axis has an angle of β=45° to the x-axis.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-3-2789

Metasurfaces have proven their great application potentials in terahertz (THz) wave modulations. However, realizing an active metasurface retaining lensing functionality in the THz frequency regime is still highly desired. Here a metalens, featuring electrically tunable focal length, based on propagation phase delay, is proposed and demonstrated experimentally. To have full control over the designed lens functionality, a gold thin film etched with a C-shaped aperture antenna array covered by monolayer graphene is used. By applying a bias voltage to the graphene, the phase control of the antenna array is changed, and thus the focus of the linearly polarized THz beam can be flexibly tuned from 7.13mm to 8.25mm. The proposed approach has a promising perspective for a variety of applications in communication, reconfigurable flat optics and real-time imaging in THz regime.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Wave Modulation by Pre-plasma Using Different Laser Wavelength

Tong Wu, Liquan Dong, Rui Zhang, Hang Zhao, Yuejin Zhao, Cunlin Zhang, Liangliang Zhang

https://link.springer.com/article/10.1007%2Fs10762-019-00618-9

We report the terahertz (THz) wave modulation from a pre-plasma using different laser wavelengths, which is intersected orthogonally to the two-color laser filament produced by 800-nm laser pulse. When the pre-plasma exists, the THz radiation excited by the two-color field decreases significantly and the modulation depth increases with the increasing modulation pulse wavelength. Moreover, the amplitude reduction at high frequency in THz spectrum and the THz wave polarization change also have the modulation pulse wavelength dependence. These results can be explained by a photocurrent model considering wavelength-dependent ionization rate. The work contributes to further understand the theoretical mechanism of THz wave generation and enrich the practical application of ultrafast THz modulator.