Abstract-THz Induced Nonlinear Effects in Materials at Intensities above 26 GW/cm2

A. Woldegeorgis, T. Kurihara, B. Beleites, J. Bossert, R. Grosse, G. G. Paulus, F. Ronneberger, A. Gopal

https://link.springer.com/article/10.1007%2Fs10762-018-0493-3

Nonlinear refractive index and absorption coefficient are measured for common semiconductor material such as silicon and organic molecule such as lactose in the terahertz (THz) spectral regime extending from 0.1 to 3 THz. Terahertz pulses with field strengths in excess of 4.4 MV/cm have been employed. Transmittance and the transmitted spectrum were measured with Z-scan and single shot noncollinear electro-optic pump-probe techniques. The THz-induced change in the refractive index (Δn) shows frequency-dependence and a maximum change of − 0.128$-0.128$ at 1.37 THz in lactose and up to + 0.169$+0.169$ at 0.15 THz in silicon was measured for a peak incident THz intensity of 26 GW/cm2. Furthermore, the refractive index variation shows a quadratic dependence on the incident THz field, implying the dominance of third-order nonlinearity.

Abstract-Enhanced spin-precession dynamics in a spin-metamaterial coupled resonator observed in terahertz time-domain measurements

T. Kurihara, K. Nakamura, K. Yamaguchi, Y. Sekine, Y. Saito, M. Nakajima, K. Oto, H. Watanabe, and T. Suemoto

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.144408

We demonstrate enhancement of the spin precession of orthoferrite ErFeO3 using the magnetic near-field produced by a split-ring resonator (SRR), using the terahertz pump-optical Faraday probe measurement. The precession amplitude was enhanced by ∼8 times when the resonance frequency of spin precession was close to the magnetic resonance of SRR. The time evolution of spin precession was successfully reproduced by a coupled spin- and SRR-resonance model mediated by the magnetic near-field. It is suggested that optimization of the metamaterial structure would further increase the enhancement factor, leading to the nonlinear control of spin dynamics using terahertz radiation.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.144408

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Abstract-Dielectric probe for scattering-type terahertz scanning near-field optical microscopy

T. Kurihara¹, K. Yamaguchi¹, H. Watanabe¹, M. Nakajima², and T. Suemoto¹

¹Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan
²Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

http://apl.aip.org/resource/1/applab/v103/i15/p151105_s1?isAuthorized=no

Dielectric material was used as the probe material for a scattering-type terahertz scanning near-field optical microscope (THz S-SNOM). It was found that the dielectric probe exhibits a strong near-field scattering signal with an amplitude comparable to that of the metallic probe. The behavior of the electric near-field around the tip was calculated using the finite-difference time-domain method, showing the field enhancement comparable to that of the metallic probe. The dielectric probe also exhibited a faster temporal response compared to the response of the metallic probe. Introduction of a non-metallic probe would enlarge the application field of the THz S-SNOM technique.

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