Abstract-Coherent detection of THz-induced sideband emission from excitons in the nonperturbative regime

K. Uchida, T. Otobe, T. Mochizuki, C. Kim, M. Yoshita, K. Tanaka, H. Akiyama, L. N. Pfeiffer, K. W. West, and H. Hirori

https://journals.aps.org/prb/accepted/43076O14Z2210330d36f6038100d0aa224fae6d98

Strong interaction of terahertz (THz) waves with excitons induces nonperturtbative optical effects such as Rabi splitting and high-order sideband generation. Here, we investigated coherent properties of THz-induced sideband emissions from GaAs/AlGaAs multi-quantum-wells, and determined the optical susceptibility of the THz dressed exciton in the nonperturbative regime. The strong dependences of both amplitude and phase of the second-order sideband emission on the THz electric field strength imply that the field ionization of the 1s exciton modifies the THz-dressed exciton's energy spectrum.

Abstract-Ultrafast Control of the Polarity of BiCoO 3 by Orbital Excitation as Investigated by Femtosecond Spectroscopy

Y. Okimoto, S. Naruse, R. Fukaya, T. Ishikawa, S. Koshihara, K. Oka, M. Azuma, K. Tanaka, and H. Hirori

Phys. Rev. Applied 7, 064016 – Published 12 June 2017

${\mathrm{https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.7.064016BiCoO}}_3$ is a perovskite-type cobalt oxide with a polar structure. We investigate the dynamics of its polar state by using photoexcitation with femtosecond visible and terahertz pulses. The intensity of the second-harmonic light, caused by a polar structure without inversion symmetry, is enhanced by more than 50% by irradiating the terahertz pulse showing an ultrafast response following the femtosecond terahertz pulse. By contrast, it is suppressed by more than 60% by exciting visible light with a 100-fs pulse width at room temperature. These results suggest not only an important role of the orbital excitation in the ${\mathrm{Co}}^{3+}$ ion but also a key to improving the nonlinear optical response, e.g., a figure of merit in nonlinear crystals on the time scale of a femtosecond.

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Abstract-Subcycle Optical Response Caused by a Terahertz Dressed State with Phase-Locked Wave Functions

K. Uchida, T. Otobe, T. Mochizuki, C. Kim, M. Yoshita, H. Akiyama, L. N. Pfeiffer, K. W. West, K. Tanaka, and H. Hirori

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.277402

The coherent interaction of light with matter imprints the phase information of the light field on the wave function of the photon-dressed electronic state. A driving electric field, together with a stable phase that is associated with the optical probe pulses, enables the role of the dressed state in the optical response to be investigated. We observed optical absorption strengths modulated on a subcycle time scale in a GaAs quantum well in the presence of a multicycle terahertz driving pulse using a near-infrared probe pulse. The measurements were in good agreement with the analytical formula that accounts for the optical susceptibilities caused by the dressed state of the excitons, which indicates that the output probe intensity was coherently reshaped by the excitonic sideband emissions.

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Abstract-Electric-Field Ionization of Gallium Acceptors in Germanium Induced by Single-cycle Terahertz Pulses

Y. Mukai, H. Hirori, K. Tanaka
http://arxiv.org/abs/1304.5825

The electric field ionization of gallium acceptors in germanium was studied by using terahertz time-domain spectroscopy after single-cycle terahertz pulse excitation. As the peak electric field of the excitation pulse increases, the distinct absorptions due to acceptor transitions centered at 2.0 and 2.2 THz decrease, and simultaneously, absorption emerges in the lower frequency region. These behaviors clearly show that the terahertz pulse ionizes neutral acceptors. The electric field dependence of the released hole density is well reproduced by a model assuming direct field-assisted tunneling of acceptors.