Publication Year: 2017, Page(s): c1
Title: Nano-Micro Conference
Volume 1: PROCEEDINGS OF THE NANO-MICRO CONFERENCE 2017
Conference Name: Nano-Micro Conference 2017
Conference Date: June 19 2017 - June 23 2017
Conference Location: Shanghai, China
Publisher: Nature Research Society
Editors: Yafei Zhang, Zhi Yang, Liying Zhang, Rong He, Zhihua Zhou
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Best Poster Award Winners Announcement
Innovation Awards Winners of Nano-Micro Conference 2017
Nano-Micro Conference, 2017, 1, 01006
Published Online: 04 October 2017 (Abstract)
Use of terahertz waves for sensing various type of materials has been an important subject of research. The target materials include biological tissues, various kind of liquids, industrial products, etc. In most of cases, water is the most important absorber of terahertz waves. It is crucial, therefore, to understand the terahertz absorption properties of water in various situations.
It is known that the terahertz absorption of water is strongly affected by the interaction with other molecules in solutions, gels, crystals, or other types of phases. In aqueous solutions, for example, the solute is stabilized by the interaction with surrounding water molecules, and the water molecules incorporated in this interaction are very often strongly bound to the solute, leading to reduced mobility and reduced terahertz absorption.
We have constructed a high-precision terahertz time-domain spectroscopy apparatus for hydration study. Results of hydration study of protein (hen egg white lysozyme) aqueous solution with several ammonium salts [1,2] is briefly described below. Terahertz absorption coefficient of the protein-salt aqueous solutions and salt aqueous solutions were obtained as a function of the salt concentration. The difference between the results of protein-salt aqueous solutions and those of salt aqueous solutions exhibits the nature of the hydration water of the protein and also the effect of salt on them. It was found that the hydration layer of the protein is affected by ions (mostly anions) added to the solution, and that so-called kosmotropic ions (structure makers), such as sulfate ion, reduce the amount of immobile hydration water, whereas chaotropic ions (structure breakers), such as thiocyanate ions, increase it. It is shown that the dynamical properties of hydration water molecules is correlated with the stability of the macromolecules, whereas their density with the solubility.
Measurements on other types of water-rich systems have shown that the mobility of water sometimes increases after hydration, or that the hydration number changes drastically upon a small change in the concentration. Study of hydration using terahertz waves is expected to produce fruitful results in various fields including solution chemistry, sol-gel science, biology, and medicine.
HongJun Liu,* Zhaolu Wang, Nan Huang, Jing Han
Nano-Micro Conference, 2017, 1, 01008
Published Online: 05 October 2017 (Abstract)
Terahertz (THz) wave is finding growing applications in various important fields such as space science, communications, and security screening . Besides sources and detectors, development of THz technologies also requires devices to guide and manipulate THz waves. The demand for high performance quasi optic components such as frequency filters, demultiplexer, attenuators, splitters, and polarizers is increasing . We theoretically propose and investigate a magnetically tunable narrow-band terahertz filter and a multi-channel THz wavelength division demultiplexer based on photonic crystal waveguide. The optical properties of the filter have been analyzed in detail. It is found that a single resonant peak with the central frequency of ~1 THz is existed in the transmission spectrum, which has a narrow full width at half maximum of <2 GHz. Moreover, under the control of an external magnetic field, transmission frequency and width of passband are adjustable, which reveals that the 2-D silicon photonic crystal waveguide with point and line defects can serve as a continuously tunable bandpass filter at the terahertz waveband. THz division demultiplexer consists of an input waveguide that perpendicularly coupled with a series of defects cavities, each of which captures the resonance frequency from the input waveguide. Coupled-mode theory and finite element method are used to analyze the transmission properties of the structure. It is found that the transmission wavelength centered around 1 THz can be adjusted by changing the geometrical parameters of defects cavities, which equals to THz waves generated by optical methods such as difference frequency generation and optical rectification.
Yuan Yuan Huang, Lipeng Zhu, Xinlong Xu*
Nano-Micro Conference, 2017, 1, 01011
Published Online: 06 October 2017 (Abstract)
Terahertz (THz) wave, bridging electronics and photonics in the electromagnetic spectrum, features many exotic properties and promising applications. However, because of low THz emission efficiency, less sensitive detectors, and few manipulating devices, THz wave is still on the horizon for practical applications since 1980s.With the application of femtosecond laser, THz surface emission spectroscopy has also been developed to serve as a sensitive and contactless tool for the optoelectronic measurement of semiconductor surfaces and interfaces. When a femtosecond laser beam impinges on the semiconductor surface, photocarriers or photodipoles are excited, which then induce THz radiation with the mechanism of photoconductivity or optical rectification. As the THz surface emission is sensitive to the surfaces and interfaces, the modification of the semiconductor surface provides a significant strategy for the design and performance evaluation of many electronic and optoelectronic devices for THz applications. In this talk, we will discuss the THz radiation mechanism for traditional semiconductors by changing the crystal orientation, exciting laser intensity, surface condition, and so on [1-4]. We will also discuss THz radiation from two-dimensional layered semiconductors under linearly polarized femtosecond laser excitation.
Ren-Hao Fan,* Ru-Wen Peng, Mu Wang
Nano-Micro Conference, 2017, 1, 01012
Published Online: 06 October 2017 (Abstract)
Here we present our recent work on tuning the polarization of terahertz waves via subwavelength metallic gratings. Firstly, we have experimentally demonstrated a linear polarization rotator that is a three-layer metallic grating structure for manipulating the polarization of broadband terahertz waves. By mechanical rotations of the composite grating layers, this freely tunable device can rotate the polarization of a linearly polarized THz wave to any desired direction with high conversion efficiency . Then we theoretically investigate the propagation of terahertz waves through a graphene-loaded metal grating under external magnetic field. It is found that resonant modes in the system can be converted between transverse-electric and transverse-magnetic polarizations due to Hall conductivity of grapheme, as a consequence, asymmetric transmission of terahertz waves through this graphene-loaded metal grating is achieved, and it can be tuned by adjusting either the external magnetic field or the Fermi level of grapheme . These tunable terahertz devices have potential applications in various areas, such as material analysis, wireless communication, and terahertz imaging.
K. Kadowaki,1,2* T. Yuasa,1 T. Tanaka,1 Y. Komori,1 R. Ota,1 G. Kuwano,1 Y. Tanabe,1 K. Nakamura,1 M. Tsujimoto,1,2 H. Minami,1,2 T. Kashiwagi,1,2 Richard A. Klemm3*
Nano-Micro Conference, 2017, 1, 01013
Published Online: 07 October 2017 (Abstract)
After the discovery of high temperature Superconductor YBa2Cu3O7-d with the superconducting transition temperature Tc=92 K, which is well above 77 K, the boiling point of liquid nitrogen, this year has become a celebrative and a commemorative 30th anniversary in the history of superconductivity research. In addition to this memorable occasion, this years is another important anniversary that ten years have passed after the discovery of terahertz electromagnetic wave emission from the mesa structure of Bi2212 single crystals . The important ingredients here is that the superconducting CuO2 double layers are built in a unit cell of the Bi2212 crystal as it is grown and are sandwiched by the insulating Bi2O2 layers, forming a stack of intrinsic Josephson junctions (IJJs). Since the electronic structure as a result of this layered crystal structure the superconducting as well as even normal state is highly two dimensional, the superconducting coupling becomes Josephson-junction like, extremely weak as measured by the c-axis critical current Jcc = 102 - 103 A/cm2 compared with Jabc = 106 - 107 A/cm2, resulting in the reduction of the superconducting plasma frequency to the level of fJ ~1011 c/s (0.2 ~ 1 meV), which is well below the superconducting gap Δ ~ 30 meV. This Josephson plasma mode can be excited by the dc-current through the nonlinear Josephson coupling effect by the dc-Josephson effect and the coherent THz emission is generated due to the ac-Josephson oscillation with the frequency fJ = (2e/h)vJ, where e is the elementary charge of electron, h Planck constant, and vJ the voltage per intrinsic Josephson junctions, when it matches well the cavity mode frequency. Although the understanding of this phenomenon has already been well established by various experiments and theoretical works , the practical limitation of the device is not well understood yet. For example, the most important issue is on what determines the maximum power extracted from one intrinsic Josephson junction, and how much power can be generated from the actual mesa structure with N-intrinsic Josephson junctions, where N is the number of intrinsic Josephson junctions in a mesa. The next issue is on what limits the maximum frequency.
The essential parameter related to two issues has evidently been thought the thermal effect due to the Joule heating by the dc-current (10 - 50 mW), which produces heat of ~MW/cm3 and naturally causes a serious temperature increase and inhomogeneity, which is often called as a hot-spot. It has been disclosed by us that the formation of the hot-spot gives only a detrimental effect on the THz radiation phenomena so that it is better to avoid it or control it to make the influence minimum on the THz emission. The heating issue has recently been studied intensively . As a result, we have achieved a frequency of 2.4 THz with a power of 30 mW  quite reproduciblly.
Recently, we have done a systematic case study on the rectangular, square, circular, triangular mesas, etc. and found an interesting fact. That is concerning the missing modes, which are expected to be as the strong emission modes but systematically disappear or are missing, perhaps, due to very weak intensities. This seems to occur especially in the degenerated symmetric cases such as in square and circular mesas. We argue this effect as a mode cancellation in the degenerated cavity modes in a symmetric mesa.
Shin’ichiro Hayashi,1,2* Kouji Nawata,2 Kodo Kawase,3 Hiroaki Minamide2
Nano-Micro Conference, 2017, 1, 01014
Published Online: 07 October 2017 (Abstract)
Over the past decade, there has been remarkable growth in the field of terahertz frequency science and engineering, which has become a vibrant, international, cross-disciplinary research activity. Wavelength conversion in nonlinear optical materials is an effective method for generating and detecting coherent terahertz waves owing to the high conversion efficiency, bandwidth, wide tunability, and room-temperature operation, and if the tuning range and the peak power can be enhanced, drastic developments in basic researches and industrial applications can be expected.
Here we demonstrate the generation of high-brightness terahertz waves using parametric wavelength conversion in a nonlinear MgO doped LiNbO3 crystal. We revealed novel parametric wavelength conversion process using stimulated Raman scattering in MgO:LiNbO3 without stimulated Brillouin scattering using recently-developed microchip Nd:YAG laser. We also demonstrated the coherent detection of generated terahertz waves using nonlinear up-conversion.
A number of applications require high brightness, that is, intense and narrowband, terahertz waves such as observing multi-photon absorption to specific excitation states. We speculate that the high-brightness terahertz wave and its visualization could be powerful tools not only for solving real world problems but also fundamental physics. We expect that these methods will open up new fields and tune up killer applications.
Wenxin Liu,* Chao Zhao, Xin Guo
Nano-Micro Conference, 2017, 1, 01015
Published Online: 08 October 2017 (Abstract)
Terahertz frequencies are among the most under developed electromagnetic spectra, even though their potential applications are promising in biochemical sensing, imaging for medical and security applications, astrophysics and remote atmospheric monitoring, and high-bandwidth communications. Among their wide applications, the lightweight, low voltage and broadband sources of high-power coherent THz radiation are important for military radar, electronic countermeasure systems and communications. Vacuum electronic devices such as the traveling wave tube amplifier (TWTA), backward wave oscillator and extended interaction oscillator show great potential for applications at the frequency because of wide band and high power. At THz band, the most critical part of small size THz vacuum sources is the slow wave structure, which determines the output performances, such as the output power and signal band. In the millimeter and sub-millimeter wave vacuum devices, the various of SWSs including coupling cavity, disk-loaded, helix and complex CC are used. However, they are not suitable for the THz band, resulting from the difficulty of fabricating and integrating.
Folded waveguide (FW) or serpentine circuits, for example, have ~10:1 aspect ratio in the waveguide height dimension. This is much larger than the ideal for both machining, which is limited by the length of the tool shank with acceptable wobble; and photolithography, which is limited by defocusing and absorption of light as it penetrates into deep photoresist. These requirements are the topic of ongoing research in the vacuum electronics community, motivated by the continued interest in high power mm-THz sources. Consequently, there is a great interest in the study and development of FW SWS. For the satisfied with requirement of high speed communication and ViSAR, the TWT has been developed. Based on the FW, the small size THz vacuum devices are developed in China, including UESTC, IECAS CETC 12 and CAEP, etc. In this talk, we report the development of small size THz vacuum devices in IECAS.
At IECAS, three kinds THz devices have been developed, such as the 0.3THz EIO, the peak power exceeds 4W. The 0.1THz EIO generates the output power is larger than 12W. Moreover, the THz TWT has been developed through the small size electron gun, high strength focusing magnetic field and high frequency structure welding. It produces the output power exceeds 2W and the band width is larger than 5GHz. Now we are developing the continued wave TWT for the power exceeds 10W and signal band width larger than 5GHz.