Abstract-Visible Measurement of Terahertz Power Based on Capsulized Cholesteric Liquid Crystal Film

Lei Wang,  Hongsong Qiu, Thanh Nhat Khoa Phan, Kosaku Kato, Boyoung Kang, Keisuke Takano, Yanqing Lu, Lujian Chen, Peng Lv, Kehan Yu, Wei Wei,  Biaobing Jin, Makoto Nakajima

file:///C:/Users/Randy/Downloads/applsci-08-02580.pdf

We demonstrate a new method to detect terahertz (THz) power using a temperature supersensitive capsulized cholesteric liquid crystal film based on the thermochromic and thermodiffusion effect, which is clearly observed. A quantitative visualization of the THz intensity up to 4.0 × 103 mW/cm2 is presented. The diameter of the color change area is linearly dependent on the THz radiation power above 0.07 mW in the steady state. Moreover, the THz power can be detected for 1 sec of radiation with a parabolic relation to the color change area. The THz power meter is robust, cost-effective, portable, and even flexible, and can be used in applications such as THz imaging, biological sensing, and inspection.

Abstract-Enhanced detection sensitivity of terahertz magnetic nearfield with cryogenically-cooled magnetooptical sampling in terbium-gallium-garnet

Applied Physics Letters

Takayuki Kurihara,  Hongsong Qiu,   Kosaku Kato, Hiroshi Watanabe, Makoto Nakajima

https://aip.scitation.org/doi/abs/10.1063/1.5037521

Due to its efficient coupling with electron spins, the application of terahertz magnetic nearfield in metallic microstructures has been attracting attention. While paramagnetic materials that exhibit magneto-optical effect have been known to enable visualization of the terahertz magnetic fields (magneto-optical sampling), the low field-detection sensitivity has been setting a practical limit to the broader application of such a method. Here we propose and experimentally demonstrate that the terahertz magnetic nearfield-detection sensitivity of magneto-optical sampling with terbium-gallium-garnet crystal can be drastically enhanced by cooling the crystal down to cryogenic temperatures in accordance with Curie's law. Our result paves the way for the efficient characterization of the terahertz magnetic nearfield in planer metamaterials.

Abstract-Enhancing terahertz magnetic near field induced by a micro-split-ring resonator with a tapered waveguide

Hongsong Qiu, Takayuki Kurihara, Hirofumi Harada, Kosaku Kato, Keisuke Takano, Tohru Suemoto, Masahiko Tani, Nobuhiko Sarukura, Masashi Yoshimura, and Makoto Nakajima

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-8-1658

Substantial enhancement of terahertz magnetic near field achieved by the combination of a tapered metallic waveguide and a micro-split-ring resonator is demonstrated. The magnetic near field is probed directly via the magneto-optic sampling with a Tb3Ga5O12${\mathrm{Tb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ crystal. The incident terahertz wave with a half-cycle waveform is generated by using the pulse-front tilting method. The magnetic near field at the resonant frequency is enhanced by more than 30 times through the combination of the waveguide and the resonator. The peak amplitude of the magnetic field with a damped oscillation waveform in the time domain is up to 0.4 T. The resonant frequency can be tuned by adopting different resonator designs. The mechanism of the enhancement is analyzed by performing calculations based on the finite element method. The strong terahertz magnetic near field enables the excitation of large-amplitude spin dynamics and can be utilized for an ultrafast spin control.

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