Abstract-Enhanced Terahertz Wave Generation from Cytop Antireflection–Coated DAST Crystal

Hirohisa Uchida, Chisa Koyama, Takeshi Takagi, Pei-bin Wang, Takayuki Kamei, Saroj R. Tripathi, Kodo Kawase, Kei Takeya

https://link.springer.com/article/10.1007/s10762-020-00674-6

There was no appropriate antireflection coating material for organic nonlinear optical (NLO) crystal used for terahertz wave generation; therefore, it was difficult to reduce Fresnel’s reflection loss of laser power used to excite the emitter crystal until we found that an amorphous polymer “Cytop” was applicable. Here, we demonstrate enhanced terahertz (THz) wave generation from an organic NLO crystal using a coating made from Cytop. With the Cytop coating, surface reflection losses of the excitation light were minimized, resulting in a significant improvement in THz wave generation over a wide frequency range.

Abstract-Pump wavelength-independent broadband terahertz generation from a nonlinear optical crystal

Kei Takeya, Koutarou Okimura, Kengo Oota, Kodo Kawase, and Hirohisa Uchida

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-17-4100

In nonlinear optical (NLO) crystals, the selection of pump light wavelengths for the generation of terahertz (THz) waves is limited due to problems associated with coherence length, refractive index, and absorption by the crystal. Relaxation of this limitation would open up potential light sources for THz generation. One such solution, Cherenkov phase matching, removes the coherence length constraint. In this study, we attempted to generate THz waves from an NLO crystal using femtosecond pulses of various wavelengths. Specifically, 805-nm and 1560-nm femtosecond pulses were used to pump a prism-coupled LiNbO3${\mathrm{LiNbO}}_3$ crystal. Broadband THz-wave generation and a THz-wave output proportional to the square of the pump light intensity were observed at both wavelengths. The generation of THz waves by prism-coupled Cherenkov phase matching was not limited by the wavelength of the pump light. Moreover, THz-wave generation at even greater intensities may be possible by optimizing the pump source and coupling to an NLO crystal.

© 2018 Optical Society of America

Abstract-Monitoring Theophylline Concentrations in Saline Using Terahertz ATR Spectroscopy

Kei Takeya 1,* , Keita Muto 1

, Yasuhiro Ishihara 2

 and Kodo Kawase 1

1 Department of Electrical and Electronic Engineering Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan2 Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan

* Author to whom correspondence should be addressed.

Academic Editor: Christoph Peter Hauri

http://www.mdpi.com/2076-3417/6/3/72

To assess the possibility of terahertz technology for the determination of drug concentration in blood, we endeavored to apply a terahertz (THz) attenuated total reflection (ATR) method to measure the levels of theophylline in saline. A change in reflected THz wave amplitude was observed in a theophylline concentration-dependent manner. This result was obtained with simple measurements of comparisons of the amplitude of the reflected wave, and suggests that it is possible to monitor concentration changes of drugs in liquid material using THz ATR measurements.

Abstract-Broadband terahertz wave generation from a MgO:LiNbO3 ridge waveguide pumped by a 1.5 μm femtosecond fiber laser

Shuzhen Fan, Hajime Takeuchi, Toshihiko Ouchi, Kei Takeya, and Kodo Kawase

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-38-10-1654

Cherenkov phase-matched terahertz (THz) wave generation from a MgO:LiNbO3 ridge waveguide was studied using optical rectification. Pumping was achieved using 20 and 60  fs laser pulses from a fiber laser centered at 1.56 μm. Time-domain spectroscopy (TDS) results showed a single-cycle pulse with 20  fs pulse pumping and a near-single-cycle pulse with 60  fs pulse pumping. The spectrum covered the range of 0.1–7 THz, with a signal-to-noise ratio of over 50  dB. The output power measured by a Si bolometer and a deuterated triglycine sulfate pyroelectric detector is shown and compared to that of a commercial photoconductive antenna. This system is believed to be a promising THz source for low-cost, compact, robust, and highly integrated TDS, THz imaging, and tomography systems.

© 2013 Optical Society of America

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