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-Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep

Da-Hye Choi, Il-Min Lee, Kiwon Moon, Dong Woo Park, Eui Su Lee, and Kyung Hyun Park

Fig. 1 Schematic of the experiment set-up. A beating signal generated from a tunable laser system is injected into the transmitter (Tx) for THz generation. The THz waves are divided by a beam splitter. The beams reflected from the two mirrors are focused on the receiver (Rx).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-10-14695

A terahertz continuous wave system is demonstrated for thickness measurement using Gouy phase shift interferometry without frequency sweep. One arm of the interferometer utilizes a collimated wave as a reference, and the other arm applies a focused beam for sample investigation. When the optical path difference (OPD) of the arms is zero, a destructive interference pattern is produced. Interference signal intensity changes induced by the OPD changes can be easily predicted by calculations. By minimizing the difference between the measured and the calculated signal against the OPD, the thicknesses of sub-100-μm-thick samples are determined at 625 GHz.

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

Abstract-Semiconductor-Based Terahertz Photonics for Industrial Applications

Eui  Su Lee, Kiwon Moon, Il-Min Lee, Hyun-Soo Kim,  Dong Woo Park,  Jeong-Woo Park,Dong Hun Lee,Sang-Pil Han, Namje Kim,Kyung Hyun Park

https://ieeexplore.ieee.org/document/8234572

In developing terahertz (THz) technologies that are more suitable for industrial applications, we have focused on research on continuous-wave (CW) THz technologies to develop small, low-cost, and multifunctional THz devices and systems. In the course of this research, we have developed several key devices such as widely tunable compact beating sources in the form of dual-mode lasers, THz emitters, including nano-electrode-photomixers and unitraveling carrier photodiode photomixers, and highly sensitive THz detectors, such as Schottky barrier diodes. In this paper, along with our recently obtained results that demonstrate the enhanced performance of these devices, we also present an example of a practical industrial application of our CW THz system: a nondestructive evaluation (NDE) system. The system described can be applied in the car manufacturing factory as an NDE technique to find process errors. Although further improvements to photonics-based THz technologies are necessary, we believe that efforts in this field will begin an era of THz technologies as a widely used industrial technique.

Abstract-Terahertz rectifier exploiting electric field-induced hot-carrier effect in asymmetric nano-electrode

Kiwon Moon, Jun-Hwan Shin, Il-Min Lee, Dong Woo Park, Eui Su Lee and Kyung Hyun Park,

http://iopscience.iop.org/article/10.1088/1361-6528/aae130/meta


Rectifiers have been used to detect electromagnetic waves with very low photon energies. In these rectifying devices, different methods have been utilized, such as adjusting the bandgap and the doping profile, or utilizing the contact potential of the metal–semiconductor junction to produce current flow depending on the direction of the electric field. In this paper, it is shown that the asymmetric application of nano-electrodes to a metal–semiconductor–metal (MSM) structure can produce such rectification characteristics, and a terahertz (THz) wave detector based on the nano-MSM structure is proposed. Integrated with a receiving antenna, the fabricated device detects THz radiation up to a frequency of 1.5 THz with responsivity and noise equivalent power of 10.8 V/W and  respectively, estimated at 0.3 THz. The unidirectional current flow is attributed to the thermionic emission of hot carriers accelerated by the locally enhanced THz field at the sharp end of the nano-electrode. This work not only demonstrates a new type of THz detector but also proposes a method for manipulating ultrafast charge-carrier dynamics through the field enhancement of the nano-electrode, which can be applied to ultrafast photonic and electronic devices.

Abstract-Photo-conductive detection of continuous THz waves via manipulated ultrafast process in nanostructures

Kiwon Moon, Eui Su Lee, Il-Min Lee, Dong Woo Park, Kyung Hyun Parka,

http://aip.scitation.org/doi/abs/10.1063/1.5008790

Time-domain and frequency-domain terahertz (THz) spectroscopy systems often use materials fabricated with exotic and expensive methods that intentionally introduce defects to meet short carrier lifetime requirements. In this study, we demonstrate the development of a nano-photomixer that meets response speed requirements without using defect-incorporated, low-temperature-grown (LTG) semiconductors. Instead, we utilized a thin InGaAs layer grown on a semi-insulating InP substrate by metal-organic chemical vapor deposition (MOCVD) combined with nano-electrodes to manipulate local ultrafast photo-carrier dynamics via a carefully designed field-enhancement and plasmon effect. The developed nano-structured photomixer can detect continuous-wave THz radiation up to a frequency of 2 THz with a peak carrier collection efficiency of 5%, which is approximately 10 times better than the reference efficiency of 0.4%. The better efficiency results from the high carrier mobility of the MOCVD-grown InGaAs thin layer with the coincidence of near-field and plasmon-field distributions in the nano-structure. Our result not only provides a generally applicable methodology for manipulating ultrafast carrier dynamics by means of nano-photonic techniques to break the trade-off relation between the carrier lifetime and mobility in typical LTG semiconductors but also contributes to mass-producible photo-conductive THz detectors to facilitate the widespread application of THz technology.

Abstract-Semiconductor-Based Terahertz Photonics for Industrial Applications

Kyung Hyun Park, Eui Su Lee, Il-MIn Lee, Kiwon Moon, Hyun-Soo Kim, Jeomg-Woo Park, Dong-Woo Park, Dong Hun Lee, and Sang-Pil Han

https://www.osapublishing.org/abstract.cfm?uri=ofc-2017-W4B.4&origin=search

With a vision of easily-accessible terahertz industrial applications, we are in pursuit of small and cost-effective terahertz technologies. Our various approaches for the enhanced performances, including arrayed devices and nano-based devices will be presented.

Abstract-Terahertz radiation using log-spiral-based low-temperature-grown InGaAs photoconductive antenna pumped by mode-locked Yb-doped fiber laser

Moon Sik Kong, Ji Su Kim, Sang Pil Han, Namje Kim, Kiwon Moon, Kyung Hyun Park, and Min Yong Jeon
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-7-7037

We demonstrate a terahertz (THz) radiation using log-spiral-based low-temperature-grown (LTG) InGaAs photoconductive antenna (PCA) modules and a passively mode-locked 1030 nm Yb-doped fiber laser. The passively mode-locked Yb-doped fiber laser is easily implemented with nonlinear polarization rotation in the normal dispersion using a 10-nm spectral filter. The laser generates over 250 mW of the average output power with positively chirped 1.58 ps pulses, which are dechirped to 127 fs pulses using a pulse compressor outside the laser cavity. In order to obtain THz radiation, a home-made emitter and receiver constructed from log-spiral-based LTG InGaAs PCA modules were used to generate and detect THz signals, respectively. We successfully achieved absorption lines over 1.5 THz for water vapor in free space. Therefore, we confirm that a mode-locked Yb-doped fiber laser has the potential to be used as an optical source to generate THZ waves.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Bias field tailored plasmonic nano-electrode for high-power terahertz photonic devices

Kiwon Moon

, Il-Min Lee

, Jun-Hwan Shin

, Eui Su Lee

, Namje Kim

, Won-Hui Lee

, Hyunsung Ko

, Sang-Pil Han

 & Kyung Hyun Park

• • http://www.nature.com/articles/srep13817

• Scientific Reports 5, Article number: 13817 (2015)
• doi:10.1038/srep13817

Photoconductive antennas with nano-structured electrodes and which show significantly improved performances have been proposed to satisfy the demand for compact and efficient terahertz (THz) sources. Plasmonic field enhancement was previously considered the dominant mechanism accounting for the improvements in the underlying physics. However, we discovered that the role of plasmonic field enhancement is limited and near-field distribution of bias field should be considered as well. In this paper, we clearly show that the locally enhanced bias field due to the size effect is much more important than the plasmonic enhanced absorption in the nano-structured electrodes for the THz emitters. Consequently, an improved nano-electrode design is presented by tailoring bias field distribution and plasmonic enhancement. Our findings will pave the way for new perspectives in the design and analysis of plasmonic nano-structures for more efficient THz photonic devices.

Abstract-Metal-VO2 hybrid grating structure for a terahertz active switchable linear polarizer

Jun-Hwan Shin1,2, Kiwon Moon1, Eui Su Lee1, Il-Min Lee1 and Kyung Hyun Park1,2

http://iopscience.iop.org/0957-4484/26/31/315203

khp@etri.re.kr

1 THz Photonics Creative Research Center, Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 305-700, Korea
2 School of Advanced Device Technology, University of Science & Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Korea 

An active terahertz (THz) wave hybrid grating structure of Au/Ti metallic grating on VO2/Al2O3 (0001) was fabricated and evaluated. In our structure, it is shown that the metallic gratings on the VO2 layer strengthen the metallic characteristics to enhance the contrast of the metallic and dielectric phases of a VO2-based device. Especially, the metal grating-induced optical conductivity of the device is greatly enhanced, three times more than that of a metallic phase of bare VO2 films in the 0.1–2.0 THz spectral range. As an illustrative example, we fabricated an actively on/off switchable THz linear polarizer. The fabricated device has shown commercially comparable values in degree of polarization (DOP) and extinction ratio (ER). A high value of 0.89 in the modulation depth (MD) for the transmission field amplitude, superior to other THz wave modulators, is achieved. The experimental results show that the fabricated device can be highly useful in many applications, including active THz linear polarizers, THz wave modulators and variable THz attenuators.

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 & Article-Continuous-wave terahertz system based on a dual-mode laser for real-time non-contact measurement of thickness and conductivity

Kiwon Moon, Namje Kim, Jun-Hwan Shin, Young-Jong Yoon, Sang-Pil Han, and Kyung Hyun Park  »View Author Affiliations
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-3-2259&id=277890

Terahertz (THz) waves have been exploited for the non-contact measurements of thickness and refractive index, which has enormous industrial applicability. In this work, we demonstrate a 1.3-μm dual-mode laser (DML)-based continuous-wave THz system for the real-time measurement of a commercial indium-tin-oxide (ITO)-coated glass. The system is compact, cost-effective, and capable of performing broadband measurement within a second at the setting resolution of 1 GHz. The thickness of the glass and the sheet conductivity of the ITO film were successfully measured, and the measurements agree well with those of broadband pulse-based time domain spectroscopy and Hall measurement results.

© 2014 Optical Society of America