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THz-Wave Generation from GaP THz Photonic Crystal Waveguides under Difference-Frequency Mixing

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Optics and Photonics Journal 2012年第3期2卷 201-205页

作者： Kyosuke Saito Tadao Tanabe yutaka oyama Department of Materials Science Graduate School of Engineering Tohoku University Sendai Japan Institute of Multidisciplinary Research for Advanced Materials Tohoku University Sendai Japan

GaP terahertz (THz) two-dimensional (2D) photonic crystal (PC) waveguides with line defects were fabricated using inductively-coupled plasma reactive-ion etching (ICP-RIE) in Ar/Cl2 gas chemistries. THz-wave generation from the fabricated PC waveguides was demonstrated under collinear phase-matched difference-frequency generation (DFG), using Cr:Forsterite (Cr:F) lasers as the incident source. We compared the THz-wave output characteristics of the PC waveguides with that of GaP planar waveguides. The collinear phase-matching conditions in the DFG process were satisfied for 300- and 500-μm-wide PC waveguide structures at 0.7 and 0.6 THz, respectively. The additional output peaks that appeared near the edge of the photonic band gap, around 0.5 THz, were attributed to the guiding modes in the PC waveguide;no such peaks appeared in the non-patterned ridge waveguides. These experimental results suggest that the phonon-polariton confinement in THz-PC waveguides based on the GaP crystal could be used to enhance the nonlinear optical effect for THz-wave generation.

关键词： THz-Wave Generation Photonic Crystal Waveguide Nonlinear Optical Effect

Calculation of the Nonlinear Susceptibility in van der Waals Crystals

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Optics and Photonics Journal 2019年第11期9卷 178-188页

作者： Mingxi Chen Chao Tang Tadao Tanabe yutaka oyama Department of Materials Science Graduate School of Engineering Tohoku University Sendai Japan

The development of theoretical models for crystals has led to the evolution of computational methods with which much more thorough investigations than previously possible can be done, including studies of the nonlinear optical properties. There has recently been a rise in interest in 2-dimensional materials;unfortunately, measurements of the nonlinear susceptibility of these materials in the wavelength range of the order of hundreds of nanometers by traditional methods are difficult. Studies of second-harmonic generation (SHG) from the transition-metal dichalcogenides (TMDCs), MoS2 and MoSe2, have been reported;however, SHG from other typical van der Waals crystals such as GaSe and other transition metal monochalcogenides (TMMCs) has rarely been studied under the same conditions. In this study, the 211 (i = 2, j = 1, k = 1) elements in the susceptibility matrices of GaSe, InSe, MoS2 and WS2 were calculated and compared. A tendency for the SHG intensity to weaken as the wavelength increases from 500 nm to 1000 nm was observed for GaSe and InSe, and, apart from some periodic fluctuations, no clear increase could be seen for these two materials in the SHG response curve in the near infrared. By comparison, MoS2 and WS2 have obvious peaks in both the visible and infrared bands. Calculations of the SHG response show peaks at around 500 nm (for GaSe), 570 (for InSe), 660 nm, 980 nm (for MoS2) and 580 nm, 920 nm (for WS2). Moreover, similarities between the SHG curves for GaSe and InSe and for MoS2 and WS2 were revealed, which may be due to the similarities found for these two groups of crystals.

关键词： Two-Dimensional Material Second-Harmonic Generation Density Functional Theory Density Functional Perturbation Theory

Non-Contact Terahertz Inspection of Water Content in Concrete of Infrastructure Buildings

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World Journal of Engineering and Technology 2018年第2期6卷 275-281页

作者： Tadao Tanabe Tomoya Kanai Kenta Kuroo Tomoya Nishiwaki yutaka oyama Department of Materials Science Graduate School of Engineering Tohoku University Sendai Japan Department of Architecture and Building Science Graduate School of Engineering Tohoku University Sendai Japan

Concrete is the most widely used for construction materials in the world. Water content of concrete is an important parameter in terms durability of concrete structures. Terahertz (THz) waves, for which concrete is a porous and absorbable material, have been studied in order to establish a new non-contact inspection technology for maintenance of concrete structures. In this study, THz transmittance and reflectance of concrete in drying process were measured with a 60 GHz GUNN diode and absorption coefficient is analyzed for concrete with various water contents. It is shown that quantitative detection below 10% is possible for the water content at surface area of concrete.

关键词： Concrete Water Content Terahertz Wave Noncontact Inspection

Terahertz Wave Generation via Nonlinear Parametric Process from <i>ε</i>-GaSe Single Crystals Grown by Liquid Phase Solution Method

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Optics and Photonics Journal 2014年第8期4卷 213-218页

作者： Kyosuke Saito Yuki Nagai Kunihiko Yamamoto Kensaku Maeda Tadao Tanabe yutaka oyama Department of Materials Science Graduate School of Engineering Tohoku University Sendai Japan Institute of Multidisciplinary Research for Advanced Materials Tohoku University Sendai Japan

Terahertz (THz)-wave generation has been conducted based on difference frequency mixing (DFM) process with phonon-polariton excitation of ε-GaSe single crystals implemented with liquid-phase solution growth using the temperature difference method under controlled vapour pressure for the first time. The type-eoo phase matching condition for the DFM process at around 10 THz is satisfied by changing the incident angle into the crystal. The maximum conversion efficiency in the present DFG process is about 10-6?J-1?using a 0.1-mm-thick GaSe single crystal with the only ε- phase polytype, which can be greater than that of the commercially available Bridgman grown GaSe crystal including both ε- and γ-phase polytypes.

关键词： Terahertz Wave Nonlinear Optics Semiconductor Material Liquid Phase Solution Growth

Room Temperature Terahertz Emission Via Intracenter Transition in Semiconductors

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Room Temperature Terahertz Emission Via Intracenter Transiti...