Abstract-Computed terahertz near-field mapping of molecular resonances of lactose stereo-isomer impurities with sub-attomole sensitivity

Kiwon Moon, Youngwoong Do, Hongkyu Park, Jeonghoi Kim, Hyuna Kang, Gyuseok Lee, Jin-Ha Lim, Jin-Woo Kim,  Haewook Han

https://www.nature.com/articles/s41598-019-53366-0

Terahertz near-field microscopy (THz-NFM) could locally probe low-energy molecular vibration dynamics below diffraction limits, showing promise to decipher intermolecular interactions of biomolecules and quantum matters with unique THz vibrational fingerprints. However, its realization has been impeded by low spatial and spectral resolutions and lack of theoretical models to quantitatively analyze near-field imaging. Here, we show that THz scattering-type scanning near-field optical microscopy (THz s-SNOM) with a theoretical model can quantitatively measure and image such low-energy molecular interactions, permitting computed spectroscopic near-field mapping of THz molecular resonance spectra. Using crystalline-lactose stereo-isomer (anomer) mixtures (i.e., α-lactose (≥95%, w/w) and β-lactose (≤4%, w/w)), THz s-SNOM resolved local intermolecular vibrations of both anomers with enhanced spatial and spectral resolutions, yielding strong resonances to decipher conformational fingerprint of the trace β-anomer impurity. Its estimated sensitivity was ~0.147 attomoles in ~8 × 10−4 μm3 interaction volume. Our THz s-SNOM platform offers a new path for ultrasensitive molecular fingerprinting of complex mixtures of biomolecules or organic crystals with markedly enhanced spatio-spectral resolutions. This could open up significant possibilities of THz technology in many fields, including biology, chemistry and condensed matter physics as well as semiconductor industries where accurate quantitative mappings of trace isomer impurities are critical but still challenging.

Abstract-Towards a Rapid Terahertz Liquid Crystal Phase Shifter: Terahertz In-Plane and Terahertz Out-Plane (TIP-TOP) Switching

Benjamin S.-Y. Ung,  Xudong Liu,  Edward P. J. Parrott,  Abhishek Kumar Srivastava,  Hongkyu Park, Vladimir G. Chigrinov, Emma Pickwell-MacPherson

http://ieeexplore.ieee.org/document/8283624/


Terahertz (THz) phase shifters are an essential component needed to realize many potential applications. Liquid crystals (LC) are commonly used at optical frequencies, yet to achieve an equivalent phase shift at THz frequencies the LC layer needs to be orders of magnitude thicker. Consequently, the time for the LC to relax back to its initial state is prohibitively slow. In this paper, we show for the first time how a thick, nematic phase LC cell can be switched actively in both directions, thereby achieving fast phase shifting of THz light. We call this THz in-plane and THz out-plane (TIP-TOP) switching. To achieve this, we have designed and fabricated a novel electrode structure, able to switch to and from both in- and out-plane orientations (TIP-TOP). The performance of the fabricated device provides an actively controllable phase delay with an ON–OFF cycle switching time of approximately 0.5 s: almost 100 times faster than the usual cycle time which exceeds 40 s. Furthermore, the analysis of the director distributions allows us to understand the causes of the asymmetric switching times. The TIP-TOP cell presents the capability to work as a low insertion loss, fast THz phase shifter and could be scaled up to realize a phased array device.

Abstract-Subsurface Nanoimaging by Broadband Terahertz Pulse Near-Field Microscopy

Kiwon Moon , Hongkyu Park , Jeonghoi Kim ,Youngwoong Do , Soonsung Lee , Gyuseok Lee ,Hyeona Kang , and Haewook Han *

Department of Electrical and Computer Engineering,POSTECH, San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, Korea

Nano Lett., Article ASAP

DOI: 10.1021/nl503998v

Publication Date (Web): December 1, 2014

Copyright © 2014 American Chemical Society

*E-mail: hhan@postech.ac.kr.

http://pubs.acs.org/doi/abs/10.1021/nl503998v?src=recsys

Combined with terahertz (THz) time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the subsurface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to ∼λ/3300, at 1 THz, while the AFM only provides a flat surface topography.

Abstract-Sub-surface nanoimaging by broadband terahertz pulse near-field microscopy

Kiwon Moon , Hongkyu Park , Jeonghoi Kim , Youngwoong Do , Soonsung Lee , Gyuseok Lee , Hyeona Kang , and Haewook Han

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl503998v

Publication Date (Web): December 1, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl503998v?journalCode=nalefd

Combined with THz time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides sub-surface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the sub-surface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to ~λ/3300, at 1 THz, while the AFM only provides a flat surface topography.

Abstract-High extinction ratio and low transmission loss thin-film terahertz polarizer with a tunable bilayer metal wire-grid structur

                                                                       

                                                                           
                                         

      
Zhe Huang, Edward P. J. Parrott, Hongkyu Park, Hau Ping Chan, and Emma Pickwell-MacPherson  »View Author Affiliations

Optics Letters, Vol. 39, Issue 4, pp. 793-796 (2014)
http://dx.doi.org/10.1364/OL.39.000793

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-4-793

A thin-film terahertz polarizer is proposed and realized via a tunable bilayer metal wire-grid structure to achieve high extinction ratios and good transmission. The polarizer is fabricated on top of a thin silica layer by standard micro-fabrication techniques to eliminate the multireflection effects. The tunable alignment of the bilayer aluminum-wire grid structure enables tailoring of the extinction ratio and transmission characteristics. Using terahertz time-domain spectroscopy (THz-TDS), a fabricated polarizer is characterized, with extinction ratios greater than 50 dB and transmission losses below 1 dB reported in the 0.2–1.1 THz frequency range. These characteristics can be improved by further tuning the polarizer parameters such as the pitch, metal film thickness, and lateral displacement.

Abstract-High extinction ratio and low transmission loss thin-film terahertz polarizer with a tunable bilayer metal wire-grid structure

Zhe Huang, Edward P. J. Parrott, Hongkyu Park, Hau Ping Chan, and Emma Pickwell-MacPherson  »View Author Affiliations

Optics Letters, Vol. 39, Issue 4, pp. 793-796 (2014)
http://dx.doi.org/10.1364/OL.39.000793

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-4-793

A thin-film terahertz polarizer is proposed and realized via a tunable bilayer metal wire-grid structure to achieve high extinction ratios and good transmission. The polarizer is fabricated on top of a thin silica layer by standard micro-fabrication techniques to eliminate the multireflection effects. The tunable alignment of the bilayer aluminum-wire grid structure enables tailoring of the extinction ratio and transmission characteristics. Using terahertz time-domain spectroscopy (THz-TDS), a fabricated polarizer is characterized, with extinction ratios greater than 50 dB and transmission losses below 1 dB reported in the 0.2–1.1 THz frequency range. These characteristics can be improved by further tuning the polarizer parameters such as the pitch, metal film thickness, and lateral displacement.

© 2014 Optical Society of America