Abstract-Scalable terahertz generation by large-area optical rectification at 80 TW laser power

Dogeun Jang, Chul Kang, Seong Ku Lee, Jae Hee Sung, Chul-Sik Kee, Seung Woo Kang, and Ki-Yong Kim

(a) Experimental setup for high-energy terahertz generation from a large-aperture LN wafer. The inset shows the incident laser beam profile. (b) Laser spectral power (black line) and spectral phase (blue line). (c) Estimated laser pulse duration as a function of laser GDD. (d) Sample pyroelectric detector signal.

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-22-5634

We demonstrate high-energy terahertz generation from a large-aperture (75-mm diameter) lithium niobate wafer by using a femtosecond laser with energy up to 2 J. This scheme utilizes optical rectification in a bulk lithium niobate crystal, where most terahertz energy is emitted from a thin layer of the rear surface. Despite its simple setup, this scheme can yield 0.19 mJ of terahertz energy with laser-to-terahertz conversion efficiencies of ∼10−4$\sim {10}^{-4}$, about 3 times better than ZnTe when pumped at 800 nm. The experimental setup is upscalable for multimillijoule terahertz generation with petawatt laser pumping.

© 2019 Optical Society of America

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-High refractive index metamaterials using corrugated metallic slots

In-Sung Lee, Ik-Bu Sohn, Chul Kang, Chul-Sik Kee, Jin-Kyu Yang, and Joong Wook Lee


https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-6-6365&origin=search

We report on a method for realizing high refractive index metamaterials using corrugated metallic slot structures at terahertz frequencies. The effective refractive index and peak index frequency can be controlled by varying the width of the air gap in the corrugated slot arrays. The phenomenon occurs because of the secondary resonance effect due to the fundamental inductive-capacitive resonance, which generates a red-shift of the fundamental resonance determined by twice the length of the corrugated metallic slots. In addition, multiple gaps in the corrugated slots act as plasmonic hotspots which have the properties of three-dimensional subwavelength confinement due to extremely strong enhancement of the terahertz waves. The versatile characteristics of the structures may have many potential applications in designing compact optical devices incorporating various functionalities and in developing highly sensitive spectroscopic/imaging systems.

© 2017 Optical Society of America

Abstract-Characteristics of terahertz wave modulation using wavelength-selective photoexcitation in pentacene/Si and TIPS pentacene/Si bilayers

Hyung Keun Yoo1, Chul Kang2, Chul-Sik Kee2, In-Wook Hwang2,a) and Joong Wook Lee3,b)
http://scitation.aip.org/content/aip/journal/adva/6/11/10.1063/1.4967781?TRACK=RSS
1 S. LSI Metrology & Inspection, Samsung Electronics, Yongin 17113, South Korea
2 Advanced Photonics Research Institute, GIST, Gwangju 500-712, South Korea
3 Department of Physics and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757, South Korea
a) Email: hwangiw@gist.ac.kr;
b) Email: leejujc@chonnam.ac.kr
AIP Advances 6, 115310 (2016); http://dx.doi.org/10.1063/1.4967781

We demonstrate the characteristics of the optical control of terahertz (THz) wave transmission in photoexcited bilayers of pentacene/Si and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene)/Si. The modulation efficiency is influenced significantly by the photoexcitation wavelength of the optical beams. Lower optical absorption of organic materials leads to higher modulation efficiency because the photocarriers excited on Si with a higher diffusion rate and mobility are far more instrumental in increasing the modulation than the excitons generated on the organic layers. Securing a sufficient depth for carrier diffusion on organic layers is also important for increasing the THz modulation efficiency. These findings may be useful for designing highly efficient and spectrally controllable THz wavemodulators.

Abstract-Optical isotropy at terahertz frequencies using anisotropic metamaterials

In-Sung Lee1, Ik-Bu Sohn2, Chul Kang2, Chul-Sik Kee2, Jin-Kyu Yang3,a) and Joong Wook Lee1,b)
http://scitation.aip.org/content/aip/journal/apl/109/3/10.1063/1.4959032
1 Department of Physics and Optoelectronics Convergence Research Center, Chonnam National University, Gwangju 500-757, South Korea
2 Advanced Photonics Research Institute, GIST, Gwangju 500-712, South Korea
3 Department of Optical Engineering, Kongju National University, Cheonan 330-717, South Korea
a) jinkyuyang@kongju.ac.kr
b) leejujc@chonnam.ac.kr
Appl. Phys. Lett. 109, 031103 (2016); http://dx.doi.org/10.1063/1.4959032

We demonstrate optically isotropic filters in the terahertz (THz) frequency range using structurally anisotropic metamaterials. The proposed metamaterials with two-dimensional arrangements ofanisotropic H-shaped apertures show polarization-independent transmission due to the combined effects of the dipole resonances of resonators and antennas. Our results may offer the potential for the design and realization of versatile THz devices and systems.

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)
 VIEW AFFILIATIONS
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.

Abstract-Terahertz modulation on angle-dependent photoexcitation in organic-inorganic hybrid structures

Hyung Keun Yoo¹, Sun-Goo Lee¹, Chul Kang¹, Chul-Sik Kee^1,2, and Joong Wook Lee

http://apl.aip.org/resource/1/applab/v103/i15/p151116_s1?isAuthorized=no

The characteristics of terahertz (THz) modulation in organic copper phthalocyanine thin films deposited on a Si wafer were investigated by angle-dependent photoexcitation. We reveal that the efficiency of THz modulation reflects not only the angle-dependent reflectivity of the organic thin films that undergo a change of complex refractive index due to photoexcitation but also the laser-induced birefringence induced by a charge density grating in the direction normal to the polarization of the excitation beams.

© 2013 AIP Publishing LLC