Abstract-Frequency-agile injection-seeded terahertz-wave parametric generation

Yoshikiyo Moriguchi, Yu Tokizane, Yuma Takida, Kouji Nawata, Shigenori Nagano, Manabu Sato, Taiichi Otsuji, and Hiroaki Minamide

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-1-77

An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) enables access to low-frequency fingerprints of molecules in the THz frequency region. However, its conventional scan repetition rate (SRR) is limited below 1 Hz. Thus, in this Letter, we propose an electrically controlled tuning system for the is-TPG, which provides high-speed scanning and random hopping agility. We achieved rapid THz frequency scanning on a pulse-by-pulse basis by employing a gain-switched laser diode and a micro-electromechanical system tunable vertical-cavity surface-emitting laser as the pump and seed lasers. A THz spectrum was acquired with a 10 times higher SRR of 10 Hz for the 1.6–3 THz range with a sampling resolution of 4.6 GHz.

© 2019 Optical Society of America

Abstract-Tunable Backward Terahertz-wave Parametric Oscillation

Kouji Nawata, Yu Tokizane, Yuma Takida,  Hiroaki Minamide,

https://www.nature.com/articles/s41598-018-37068-7

Backward optical parametric oscillation has attracted attention for cavityless spectral narrowband generation based on perfect photon conversion. Few demonstrations have shown its potential from the aspect of nonlinear photonics; therefore, the mechanisms of momentum conservation among interacting light waves have been concealed by the restricted configuration under the phase-matching condition of periodically poled structures. Here, we unveil a tunable mechanism in the terahertz region by active control of the phase-matching condition. The tunability of backward terahertz-wave parametric oscillation is investigated using a quasi-collinear phase-matching model and its frequency range from the sub-terahertz to terahertz region is identified. Transform-limited terahertz-wave pulse is achieved simply by installing a device on the pump propagating line with no cavity. Moreover, the cascading terahertz-wave generation enhances the photon conversion efficiency, thus making nonlinear optics and its applications more promising. The results highlight new capabilities for using modern ferroelectric materials and encourage further research on nonlinear optics.

Abstract-High-average and high-peak output-power terahertz-wave generation by optical parametric down-conversion in MgO:LiNbO3

Applied Physics Letters

Yoshikiyo Moriguchi,  Yu Tokizane, Yuma Takida, Kouji Nawata,   Taizo Eno, Shigenori Nagano,  Hiroaki Minamide,

Schematic of the experimental setup for THz-wave generation at a pulse repetition frequency of 100 kHz. ISO, isolator; PBS, polarization beam splitter; FR, Faraday rotator; and HWP, half-wave plate.

https://aip.scitation.org/doi/abs/10.1063/1.5046126

A widely tunable terahertz (THz)-wave generation that has a high repetition rate and a narrow line width is demonstrated in this paper by injection-seeded THz-wave parametric generation (is-TPG) in a MgO:LiNbO3 crystal. By pumping the crystal using a passively Q-switched neodymium-doped yttrium vanadate microchip laser with a time duration of 140 ps and an average power of up to 5 W, a THz-wave output with an average output power of 30 μW, a peak power of 4 W, a pulse duration of 73 ps, and a pulse-repetition frequency of 100 kHz is obtained. To prevent laser damage and photorefractive damage to the crystal, the constraints on the pumping condition of the MgO:LiNbO3 crystal are experimentally studied by changing the pumping parameters. As a result, we achieved the stable generation of the THz-wave signal in the 100 kHz regime. Moreover, we performed THz-wave imaging by using the developed is-TPG source. The obtained THz image indicated that the developed system has a good stability over long periods of time.

Abstract-Off-resonance and in-resonance metamaterial design for a high-transmission terahertz-wave quarter-wave plate

Zhengli Han, Seigo Ohno, Yu Tokizane, Kouji Nawata, Takashi Notake, Yuma Takida, and Hiroaki Minamide

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-12-2977

This Letter describes a novel metamaterial design by employing off-resonance and in-resonance excitation for a high-transmission terahertz-wave quarter-wave plate (QWP). The device is demonstrated with a thin film metamaterial with double-layer split ring resonators (SRRs). Different from a usual resonant metamaterial device, here we design the work frequency off from the inductor-capacitor (LC) resonance for the TE mode, while in a dipole resonance for the TM mode to obtain the artificial birefringence. Rectangular SRRs in this Letter provide a choice to optimize the off-resonance and in-resonance excitation, to assist the double-layer design for high transmission. Converting a linearly polarized wave to circular polarization with our QWP, the experiment confirms a transmittance of 0.8 and an ellipticity of 0.99 at 0.98 THz. The developed thin film device is flexible and has a thickness of 48 μm (sub-wavelength). This is an advantage for potential integration in systems where overall device compactness is required.

© 2018 Optical Society of America

Abstract-Thin terahertz-wave phase shifter by flexible film metamaterial with high transmission

Zhengli Han, Seigo Ohno, Yu Tokizane, Kouji Nawata, Takashi Notake, Yuma Takida, and Hiroaki Minamide

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-25-31186

Thin terahertz (THz)-wave optical components are fundamentally important for integrated THz-wave spectroscopy and imaging systems, especially for phase manipulation devices. As described herein, a thin THz-wave phase shifter was developed using a flexible film metamaterial with high transmission and polarization independent properties. The metamaterial unit structure employs double-layer un-split ring resonators (USRRs) with a designed distance between the two layers to obtain phase retardance of π/2, thus constituting a THz-wave phase shifter. The metamaterial design keeps the transmission coefficient as high as 0.91. The phase shifter also has polarization independence due to the four-fold symmetry of the USRR structure. Because of the subwavelength feature size of the USRR, this shifter can offer benefits for manipulating the spatial profile for the THz-wave phase through design of a binary optics phase plate by arranging a USRR array. The thickness of 48 μm has benefits for developing integrated THz optics and other applications that demand compactness and flexibility. The developed film size of 5 cm × 5 cm from the device fabrication process is suitable for THz lenses or gratings of large optical components.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing 

Abstract- Terahertz-wave parametric gain of stimulated polariton scattering

Yuma Takida, Jun-ichi Shikata, Kouji Nawata, Yu Tokizane, Zhengli Han, Mio Koyama, Takashi Notake, Shin'ichiro Hayashi, and Hiroaki Minamide

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.043836

We have experimentally determined the terahertz- (THz-) wave parametric gain of stimulated Raman scattering (SRS) by phonon-polaritons in LiNbO3. Our approach is based on ultrabright THz-wave generation from SRS under stimulated Brillouin scattering suppression with subnanosecond pump pulses. To obtain the frequency dependence of the parametric gain, we measured the crystal-length dependence of the THz-wave output directly using a surface-coupling configuration. We found that the product of the parametric gain and the threshold crystal length is constant throughout the tuning range. Our result provides a physical basis for the design and performance enhancement of SRS-based ultrabright tabletop THz-wave sources for various applications.

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Abstract-Terahertz-wave parametric gain of stimulated polariton scattering

Yuma Takida, Jun-ichi Shikata, Kouji Nawata, Yu Tokizane, Zhengli Han, Mio Koyama, Takashi Notake, Shin’ichiro Hayashi, and Hiroaki Minamide

https://journals.aps.org/pra/accepted/9b07fY8bY8f1004d36744e58e4d414a59136e3566

We have experimentally determined the terahertz (THz)-wave parametric gain of stimulated Raman scattering (SRS) by phonon-polaritons in LiNbO3. Our approach is based on ultra-bright THz-wave generation from SRS under stimulated Brillouin scattering suppression with sub-nanosecond pump pulses. To obtain the frequency dependence of the parametric gain, we measured the crystal-length dependence of the THz-wave output directly using a surface-coupling configuration. We found that the product of the parametric gain and the threshold crystal length is constant throughout the tuning range. Our result provides a physical basis for the design and performance enhancement of SRS-based ultra-bright table-top THzwave sources for various applications.