Abstract-Mechanical Terahertz Modulation Based on Single-Layered Graphene

Long Cheng, Zuanming Jin, Zongwei Ma, Fuhai Su, Yang Zhao, Yongzhuan Zhang, Tongyu Su, Yan Sun, Xueli Xu, Zhi Meng, Yuecheng Bian, Zhigao Sheng


http://onlinelibrary.wiley.com/doi/10.1002/adom.201700877/full

The 2D terahertz (THz) modulator, enabling efficient manipulation of such versatile band in nanoscale, is crucial for THz microdevices and systems, but its implementation is difficult and remains challenging in practice. Here, a novel 2D THz modulator based on single-layered graphene under mechanical strain is demonstrated. Bidirectional, i.e., both positive and negative, THz modulation effect is realized by utilizing unconventionally distributed strains on graphene. Such mechanical modulation is found to be stable and reversible, and its modulation depth can exceed 26% at 1 THz under 10–2 GPa strain. Observations of both the strain and frequency dependent modulation behavior evidence the mechanical strain-induced change of the Dirac-like energy dispersion in graphene, which is distinctive from that of the electrical and optical approaches. Due to the reliability and wide applicability of mechanical forces, these results provide an alternative route for chip-scale THz modulation devices based on 2D materials.

Abstract-Terahertz magnetic circular dichroism induced by exchange resonance in CoCr2O4 single crystal

Peng Zhang, Fuhai Su, Shile Zhang, Hongying Mei, Chao Zhang, Xuan Luo, Jianming Dai, and Li Pi
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-14-17805

Terahertz (THz) time domain spectroscopy (THz-TDS) of a CoCr2O4 single crystal has been performed under magnetic fields up to 8 Tesla. The magnetic field dependences of inter-sublattice exchange resonance at different temperatures have been investigated. Benefiting from the phase and polarization sensitive detection technique in THz-TDS, the circular absorption dichroism and Faraday ellipticity in the THz frequency region are observed and are found to be tunable by the external magnetic field. The complex indices of refraction are obtained under different magnetic field, which present distinct rotatory dispersions arising from the exchange magnetic resonance.

© 2015 Optical Society of America

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Abstract-Ultrafast imaging of terahertz Cherenkov waves and transition-like radiation in LiNbO3

Ultrafast imaging of terahertz Cherenkov waves and transition-like radiation in LiNbO3 Zhenyou Wang, FuHai Su, and Frank A. Hegmann  »View Author Affiliations

Optics Express, Vol. 23, Issue 6, pp. 8073-8086 (2015)
http://dx.doi.org/10.1364/OE.23.008073

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-6-8073

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We use ultrafast phase-contrast imaging to directly observethe cone-like terahertz (THz) Cherenkov wave generated by optical rectification of femtosecond laser pulses focused into bulk lithium niobate (LiNbO₃) single crystals. The transverse imaging geometry allows the Cherenkov angle, THz wave velocity, and optical pump pulse group velocity to be measured. Furthermore, transition-like THz radiation generated by the femtosecond laser pulse at the air-crystal boundary is observed. The effect of optical pump pulse polarization on the generation of THz Cherenkov waves and transition-like radiation in LiNbO₃is also investigated.

© 2015 Optical Society of America

Abstract-Extraordinary terahertz absorption bands observed in micro/nanostructured Au/polystyrene sphere arrays

http://www.nanoscalereslett.com/

Guotao Duan, Fuhai Su, Wen Xu, Cunlin Zhang and Weiping Cai

Terahertz (THz) time-domain spectroscopy is carried out for micro/nanostructured periodic Au/dielectric sphere arrays on Si substrate. We find that the metal-insulator transition can be achieved in THz bandwidth via varying sample parameters such as the thickness of the Au shell and the diameter of the Au/dielectric sphere. The Au/polystyrene sphere arrays do not show metallic THz response when the Au shell thickness is larger than 10 nm and the sphere diameter is smaller than 500 nm. This effect is in sharp contrast to the observations in flat Au films on Si substrate. Interestingly, the Au/polystyrene sphere arrays with a 5-nm-thick Au shell show extraordinary THz absorption bands or metallic optical conductance when the diameter of the sphere is larger than 200 nm. This effect is related to the quantum confinement effect in which the electrons in the structure are trapped in the sphere potential well of the gold shell.