Abstract-Electrical control of terahertz frequency conversion from time-varying surfaces

Kanghee Lee, Jagang Park, Jaehyeon Son, Bong Joo Kang, Won Tae Kim, Seong Cheol Lee, Bumki Min,  Fabian Rotermund,

Fig. 1 Experimental information. (a) Schematic of experimental setup. (b) Spectrum of single-cycle THz waves generated from LiNbO3 crystal with waveform in time domain (inset). (c) Spectrum of multi-cycle THz waves modulated through stacked band-pass filters with waveform in time domain (inset).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-9-12762

We investigate the electrical control of frequency conversion from a time-varying interdigitated photo-conductive antenna (IPCA) and time-varying metasurface in the terahertz (THz) frequency range. Ultrafast near-infrared (NIR) optical pulses rapidly modify the conductivities of the IPCA and metasurface; however, external voltages can retard this conductivity transition. Thus, external voltages can be used to control the frequency conversion process based on the interaction between the THz waves and the time-varying surfaces. In the IPCA, both frequency up- and down-conversion processes are suppressed by external voltages. However, in the metasurface, the down-conversion is dramatically suppressed by external voltages, whereas the suppression on the up-conversion is less effective.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Linear frequency conversion via sudden merging of resonances in time-variant terahertz metasurfaces

Kanghee Lee,   Jaehyeon Son,   Byungsoo Kang,   Jagang Park,  Fabian Rotermund,  Bumki Min

http://ieeexplore.ieee.org/document/8067111/


We experimentally demonstrate linear frequency conversion on time-variant terahertz (THz) metasurface. The proposed metasurface is originally designed to have two resonances, and with optical pumping, the resonances are merged into one. When a THz pulse passes through the metasurface during this merging process, a frequency component corresponding to the merged mode is generated.

Abstract-Electrically Controlled Second-Order Nonlinear Generation of Terahertz Waves

Kanghee Lee, Jagang Park, Bong Joo Kang, Won Tae Kim, Bumki Min, and Fabian Rotermund
https://www.osapublishing.org/abstract.cfm?uri=NLO-2017-NW3A.2

We report electric-field-induced second-harmonic generation of terahertz waves in photodoped gallium arsenide with direct-current bias fields. A fundamental wave of 0.6 THz was selectively incident and its second-harmonic wave of 1.2 THz was clearly observed.

© 2017 OSA

Abstract-Control of terahertz nonlinear transmission with electrically gated graphene metadevices

• Hyun Joo Choi
• , In Hyung Baek
• , Bong Joo Kang
• , Hyeon-Don Kim
• , Sang Soon Oh
• , Joachim M. Hamm
• , Andreas Pusch
• , Jagang Park
• , Kanghee Lee
• , Jaehyeon Son
• , Young U. k. Jeong
• , Ortwin Hess
• , Fabian Rotermund
•  & Bumki Min

http://www.nature.com/articles/srep42833?WT.feed_name=subjects_materials-science

Graphene, which is a two-dimensional crystal of carbon atoms arranged in a hexagonal lattice, has attracted a great amount of attention due to its outstanding mechanical, thermal and electronic properties. Moreover, graphene shows an exceptionally strong tunable light-matter interaction that depends on the Fermi level - a function of chemical doping and external gate voltage - and the electromagnetic resonance provided by intentionally engineered structures. In the optical regime, the nonlinearities of graphene originated from the Pauli blocking have already been exploited for mode-locking device applications in ultrafast laser technology, whereas nonlinearities in the terahertz regime, which arise from a reduction in conductivity due to carrier heating, have only recently been confirmed experimentally. Here, we investigated two key factors for controlling nonlinear interactions of graphene with an intense terahertz field. The induced transparencies of graphene can be controlled effectively by engineering meta-atoms and/or changing the number of charge carriers through electrical gating. Additionally, nonlinear phase changes of the transmitted terahertz field can be observed by introducing the resonances of the meta-atoms.