Abstract-Generation of arbitrarily chirped and CEP-controlled terahertz pulses for dispersion compensation using an optical pulse shaping technique and a fan-out periodically poled crystal

Hisanari Takahashi, Yoichi Kawada, Hiroshi Satozono, Koji Takahashi, Koyo Watanabe, Takashi Inoue, and Hironori Takahashi

Fig. 1. A concept for generating phase-controlled THz pulses. THz-BS: THz beam splitter; SLM: spatial light modulator.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-18-25305

We constructed a system that can generate phase-controlled terahertz (THz) pulses using a fan-out periodically poled lithium tantalate crystal and an optical pulse shaper containing a spatial light modulator. The phase of each THz frequency components could be controlled by manipulating the delay time of the corresponding optical pulses. Using the system, we generated arbitrarily group-velocity-dispersion-controlled THz pulses, where the chirp parameter was 2.53 ps2/rad between 0.6 and 1.5 THz. In addition, we generated arbitrarily carrier-envelope-phase-controlled THz pulses in the same system. Phase-controlled THz pulses may be useful for applications such as dispersion compensation.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tailoring Single-Cycle Near Field in a Tunnel Junction with Carrier-Envelope Phase-Controlled Terahertz Electric Fields

Katsumasa Yoshioka, Ikufumi Katayama, Yusuke Arashida, Atsuhiko Ban, Yoichi Kawada, Kuniaki Konishi, Hironori Takahashi,  Jun Takeda,

https://pubs.acs.org/doi/10.1021/acs.nanolett.8b02161

Light-field-driven processes occurring under conditions far beyond the diffraction limit of the light can be manipulated by harnessing spatiotemporally tunable near fields. A tailor-made carrier envelope phase in a tunnel junction formed between nanogap electrodes allows precisely controlled manipulation of these processes. In particular, the characterization and active control of near fields in a tunnel junction are essential for advancing elaborate manipulation of light-field-driven processes at the atomic-scale. Here, we demonstrate that desirable phase-controlled near fields can be produced in a tunnel junction via terahertz scanning tunneling microscopy (THz-STM) with a phase shifter. Measurements of the phase-resolved subcycle electron tunneling dynamics revealed an unexpected large carrier-envelope phase shift between far-field and near-field single-cycle THz waveforms. The phase shift stems from the wavelength-scale feature of the tip–sample configuration. By using a dual-phase double-pulse scheme, the electron tunneling was coherently manipulated over the femtosecond time scale. Our new prescription—in situ tailoring of single-cycle THz near fields in a tunnel junction—will offer unprecedented control of electrons for ultrafast atomic-scale electronics and metrology

Abstract-Carrier envelope phase shifter for broadband terahertz pulses

Yoichi Kawada, Takashi Yasuda, and Hironori Takahashi

We demonstrated controlled shifting of the internal phase of broadband terahertz (THz) pulses. The internal phase of an ultrashort pulse is called the carrier envelope phase (CEP), which is an important parameter in the interaction of few-cycle light pulses and matter. Our CEP shifter utilizes the ultra-broadband feature of prism wave plates. We analytically derived the amount of CEP shift achievable by the CEP shifter using Jones matrixes. THz time-domain measurements clearly showed the shift of the CEP, and the results agreed well with the calculated values. The CEP shift was as high as 2𝜋, indicating that any CEP values can be chosen using our CEP shifter.

© 2016 Optical Society of America

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Abstract-Evaluation of Drug Crystallinity in Aqueous Suspension Using Terahertz Time-Domain Attenuated Total Reflection Spectroscopy

1. Gen Takebe^*, 
2. Yoichi Kawada, 
3. Koichiro Akiyama, 
4. Hironori Takahashi, 
5. Hisayoshi Takamoto, 
6. Mitsuo Hiramatsu

http://onlinelibrary.wiley.com/doi/10.1002/jps.23716/abstract

Terahertz pulsed spectroscopy has recently been demonstrated to be a novel technique for the investigation of the solid-state properties of pharmaceutical materials. In this study, we directly measured the crystallinity of a drug suspended in water, using a terahertz pulsed attenuated total reflection (ATR) method. The dihydropyridine calcium channel blocker nifedipine is classified as a poorly soluble drug; its most stable crystalline form is known as form I. Transmission spectra, collected from 0.2 to 2.0 THz (6.6 to 66 cm⁻¹), of nifedipine crystals had a strong absorption peak at 1.2 THz (40 cm⁻¹) at room temperature. When the nifedipine crystals were mixed with poloxamer 188 and suspended in water, the resulting spectra measured using the ATR method had a peak at the same frequency as in the spectra obtained in transmission mode. Furthermore, the peak area was proportional to the amount of crystals. The upward sloping baseline in the spectra, corresponding to water absorption, decreased stepwise with increasing amounts of crystalline particles. We confirmed that the spectra gave excellent quantitative results, using partial least-squares regression analysis. The results suggest the possibility of using this method for qualitative and quantitative assessments of crystalline drugs in suspension. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci