Abstract-Terahertz polarization spectroscopy in the near-field zone of a sub-wavelength-scale metal slit

Daehoon Han, Kanghee Lee, Hanlae Jo, Yunheung Song, Minhyuk Kim, and Jaewook Ahn
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-19-21276

Time-domain spectroscopy is used to probe the polarization dependence of the terahertz-frequency absorption of α-lactose molecules in the near-field vicinity of a sub-wavelength-scale metal slit. The experimental result finds that the 0.53-THz absorption of this material has an unexpected polarization dependence, strongly coupled to the slit orientation; in particular, the electric wave in parallel polarization exhibits even complete vanishing of the otherwise resonant strong absorption. The physics behind this phenomena may be explained based on the Bethe’s sub-wavelength diffraction: the electric field that is measured in the far field, but diffracted from a sub-wavelength-scale metal aperture, originates from solely magnetic dipole radiation and not from the electric dipole radiation, thus showing no electrically-coupled material response.

© 2016 Optical Society of America

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Abstract-Terahertz transmission resonances in complementary multilayered metamaterial with deep subwavelength interlayer spacing

Muhan Choi1, Byungsoo Kang2,3, Yoonsik Yi3, Seung Hoon Lee2, Inbo Kim1, Jae-Hyung Han1, Minwoo Yi4, Jaewook Ahn4 and Choon-Gi Choi3,a)
http://scitation.aip.org/content/aip/journal/apl/108/20/10.1063/1.4950863
1 School of Electronics Engineering, Kyungpook National University, Daegu 41566, South Korea
2 Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
3 Creative Research Center for Graphene Electronics, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, South Korea
4 Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
a) Electronic mail: cgchoi@etri.re.kr.
Appl. Phys. Lett. 108, 201103 (2016); http://dx.doi.org/10.1063/1.4950863

We introduce a flexible multilayered THz metamaterial designed by using the Babinet's principle with the functionality of narrow band-pass filter. The metamaterial gives us systematic way to design frequency selective surfaces working on intended frequencies and bandwidths. It shows highly enhanced transmission of 80% for the normal incident THz waves due to the strong coupling of the two layers of metamaterial complementary to each other.

Abstract-Subwavelength silicon through-hole arrays as an all-dielectric broadband terahertz gradient index metamaterial

Sang-Gil Park^1,2, Kanghee Lee^2,3, Daehoon Han^2,3, Jaewook Ahn^2,3 and Ki-Hun Jeong^1,2,a)
http://scitation.aip.org/content/aip/journal/apl/105/9/10.1063/1.4894054
1 Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea
2 KAIST Institute for Optical Science and Technology, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea
3 Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, South Korea
a) Author to whom correspondence should be addressed. Electronic mail: kjeong@kaist.ac.kr
Appl. Phys. Lett. 105, 091101 (2014); http://dx.doi.org/10.1063/1.4894054

Structuring at subwavelength scales brings out artificial media with anomalous optical features called metamaterials. All-dielectric metamaterials have high potential for practical applications over the whole electromagnetic spectrum owing to low loss and optical isotropy. Here, we report subwavelength silicon through-hole arrays as an all-dielectric gradient indexmetamaterial with broadband THz operation. The unit cell consists of a single subwavelength through-hole on highly resistive monocrystalline silicon. Depending on the fill-factor and period, the effective index was linearly modulated at 0.3–1.6 THz. The experimental results also demonstrate silicon gradient refractive index (Si-GRIN) lenses with parabolic index profiles through the spatial modification of a single unit cell along the radial direction. Si-GRIN lenseseither focus 0.4–1.6 THz beam to the diffraction-limit or serve as a flat and thin solid immersion lens on the backside of THz photoconductive antenna for highly efficient pulse extraction. This all-dielectric gradient index metamaterial opens up opportunities for integrated THz GRINoptics.

Abstract-Terahertz lens made out of natural stone

Daehoon Han, Kanghee Lee, Jongseok Lim, Sei Sun Hong, Young Kie Kim, and Jaewook Ahn  »View Author Affiliations

Terahertz (THz) time-domain spectroscopy probes the optical properties of naturally occurring solid aggregates of minerals, or stones, in the THz frequency range. Refractive index and extinction coefficient measurement reveals that most natural stones, including mudstone, sandstone, granite, tuff, gneiss, diorite, slate, marble, and dolomite, are fairly transparent for THz frequency waves. Dolomite in particular exhibits a nearly uniform refractive index of 2.7 over the broad frequency range from 0.1 to 1 THz. The high index of refraction allows flexibility in lens designing with a shorter accessible focal length or a thinner lens with a given focal length. Good agreement between the experiment and calculation for the THz beam profile confirms that dolomite has high homogeneity as a lens material, suggesting the possibility of using natural stones for THz optical elements.

© 2013 Optical Society of America