Saturday, August 27, 2016

Abstract-Self-polarized terahertz magnon absorption in a single crystal of BiFeO3


Eiichi Matsubara, Takeshi Mochizuki, Masaya Nagai, and Masaaki Ashida

We report the polarization dependence of terahertz magnon absorption in single crystals of BiFeO3grown by a modified floating zone method. In a (111)pc-oriented crystal, two major magnon absorption signals were observed for all terahertz polarizations, which indicates that magnetic domains were not aligned in one of the three allowed directions. In contrast, the absorption modes in a (001)pc-oriented crystal showed significant polarization dependence, which was unchanged even after annealing the crystal at temperatures far above the Néel point to demagnetize it. This polarization dependence coincides with that of E mode phonons. Thus, we conclude that magnon and phonon in BiFeO3 are strongly coupled and the selection rules for magnon absorption are governed by the activity of E mode phonons, namely, the crystalline anisotropy originating from ferroelectric polarization.
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Friday, August 26, 2016

Abstract-Terahertz continuous wave nonlinear-optical detection without phase-locking between a source and the detector


Vladimir V. Kornienko, Sergey A. Savinov, Yury A. Mityagin, and Galiya Kh. Kitaeva

We demonstrate the possibility of nonlinear-optical detection of terahertz (THz) wave radiation without phase-locking between a source and a detector. Spectrally resolved room-temperature incoherent nonlinear-optical detection is demonstrated for 0.22-THz continuous wave (CW) radiation by upconversion using a 100-mW CW laser in a 15-mm-long Mg:LiNbO3 crystal.
© 2016 Optical Society of America
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Abstract-Optimization of the THz Radiation from Superconductor at Non-laminar Regime


Mehdi Hosseini 

http://www.sciencedirect.com/science/article/pii/S0921453416301277

The THz radiation due to the flux flow in a superconductor slab at non-laminar regime has been investigated and the radiated power spectrum has been calculated. The parameter (τ) is defined to show amount of non-laminarity. The results reveal that for small values of τ, the system radiated at the harmonics of famous washboard frequency. However, for large values of τ, the radiation spectrum will be changed and for extreme values of τ, the peaks will be flat. Therefore the washboard picture is not valid anymore. The results show that the radiation power is optimum for the special value of τ. Also, the results compared with other theoretical and experimental data

Abstract-Investigation of mechanism: spoof SPPs on periodically textured metal surface with pyramidal grooves



https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=4769349778953500837

In microwave and terahertz frequency band, a textured metal surface can support spoof surface plasmon polaritons (SSPPs). In this paper, we explore a SSPPs waveguide composed of a metal block with pyramidal grooves. Under the deep subwavelength condition, theoretical formulas for calculation of dispersion relations are derived based on the modal expansion method (MEM). Using the obtained formulas, a general analysis is given about the properties of the SSPPs in the waveguides with upright and downward pyramidal grooves. It is demonstrated that the SSPPs waveguides with upright pyramidal grooves give better field-confinement. Numerical simulations are used to check the theoretical analysis and show good agreement with the analytical results. In addition, the group velocity of the SSPPs propagating along the waveguide is explored and two structures are designed to show how to trap the SSPPs on the metal surface. The calculation methodology provided in this paper can also be used to deal with the SSPPs waveguides with irregular grooves.

Thursday, August 25, 2016

Abstract-Ultra-Broadband Linear Polarization Conversion via Diode-Like Asymmetric Transmission with Composite Metamaterial for Terahertz Waves



    Yongzhi Cheng, Rongzhou Gong, Lin Wu,
http://link.springer.com/article/10.1007/s11468-016-0365-4
In this paper, a tri-layer metamaterial composed of a split-disk structure array sandwiched with two layers of twisted sub-wavelength metal grating is proposed and investigated numerically in terahertz region. The numerical results exhibit that linear polarization conversion via diode-like asymmetric transmission for terahertz waves within ultra-broadband frequency range is achieved due to Fabry-Perot-like resonance. In our design, the conversion polarization transmission coefficient for normal incidence is greater than 90 % in the range of 0.23–1.17 THz, equivalent to 134.3 % relative bandwidth. The physical mechanism of the broadband linear polarization conversion effect is further illustrated by simulated electrical field distributions.