Abstract-Sub-cycle Control of Optical Response by Using a Terahertz Excitonic Dressed State

Gyuseok Lee, Inhee Maeng, Chul Kang, Myoung-Kyu Oh, Chul-Sik Kee

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-26-10-13677&id=389598

Optically tunable, strong polarization-dependent transmission of terahertz pulses through aligned Ag nanowires on a Si substrate is demonstrated. Terahertz pulses primarily pass through the Ag nanowires and the transmittance is weakly dependent on the angle between the direction of polarization of the terahertz pulse and the direction of nanowire alignment. However, the transmission of a terahertz pulse through optically excited materials strongly depends on the polarization direction. The extinction ratio increases as the power of the pumping laser increases. The enhanced polarization dependency is explained by the redistribution of photocarriers, which accelerates the sintering effect along the direction of alignment of the Ag nanowires. The photocarrier redistribution effect is examined by the enhancement of terahertz emission from the sample. Oblique metal nanowires on Si could be utilized for designing optically tunable terahertz polarization modulators.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Strong polarization-dependent terahertz modulation of aligned Ag nanowires on Si substrate

Gyuseok Lee, Inhee Maeng, Chul Kang, Myoung-Kyu Oh, and Chul-Sik Kee

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-26-10-13677&id=389598

Optically tunable, strong polarization-dependent transmission of terahertz pulses through aligned Ag nanowires on a Si substrate is demonstrated. Terahertz pulses primarily pass through the Ag nanowires and the transmittance is weakly dependent on the angle between the direction of polarization of the terahertz pulse and the direction of nanowire alignment. However, the transmission of a terahertz pulse through optically excited materials strongly depends on the polarization direction. The extinction ratio increases as the power of the pumping laser increases. The enhanced polarization dependency is explained by the redistribution of photocarriers, which accelerates the sintering effect along the direction of alignment of the Ag nanowires. The photocarrier redistribution effect is examined by the enhancement of terahertz emission from the sample. Oblique metal nanowires on Si could be utilized for designing optically tunable terahertz polarization modulators.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-High-efficiency optical terahertz modulation of aligned Ag nanowires on a Si substrate

Gyuseok Lee, Inhee Maeng, Chul Kang,   Myoung-Kyu Oh,  Chul-Sik Kee,

https://aip.scitation.org/doi/abs/10.1063/1.5008485

High-efficiency optical modulation of a terahertz pulse transmitted through aligned silver nanowires on a silicon substrate is demonstrated. Without optical excitation, the terahertz pulses mostly pass through the silver nanowires. However, an optically excited sample significantly modulates the transmittance compared with an excited silicon substrate. The enhanced modulation efficiency is explained by the redistribution effect of photo-carriers due to the nanowires. The simple structure of metal nanowires on a semiconductor substrate could be useful in implementing optically tunable terahertz wave modulators.

Abstract-Strong emission of terahertz radiation from nanostructured Ge surfaces

Chul Kang¹, Jung Woo Leem², Inhee Maeng¹, Tae Heon Kim³, Jong Seok Lee³,Jae Su Yu^2,a) and Chul-Sik Kee^1,b)
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a) E-mail: jsyu@khu.ac.kr
b) E-mail: cskee@gist.ac.kr
Appl. Phys. Lett. 106, 261106 (2015); http://dx.doi.org/10.1063/1.4923372

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.