Abstract-High-throughput terahertz spectral line imaging using an echelon mirror

Gaku Asai, Daiki Hata, Shintaro Harada, Tatsuki Kasai, Yusuke Arashida, and Ikufumi Katayama

 Experimental setup for THz spectral line imaging using an echelon mirror. TL: THz Tsurupika lenses. TCL: THz cylindrical lens, CL: cylindrical lens, EOC: electro-optic crystal, Pol: polarizer, QWP: quarterwave plate.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-3-3515&id=446807

This work demonstrates terahertz (THz) line imaging that acquires broadband spectral information by combining echelon-based single-shot THz spectroscopy with high-sensitivity phase-offset electrooptic detection. An approximately 40 dB signal-to-noise ratio is obtained for a THz spectrum from a single line of the camera, with a detection bandwidth up to 2 THz at the peak electric-field strength of 1.2 kV/cm. The spatial resolution of the image is confirmed to be diffraction limited for each spectral component of the THz wave. We use the system to image sugar tablets by quickly scanning the sample, which illustrates the capacity of the proposed spectral line imaging system for high-throughput applications.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Subcycle Transient Scanning Tunneling Spectroscopy with Visualization of Enhanced Terahertz Near Field

Shoji Yoshida, Hideki Hirori, Takehiro Tachizaki, Katsumasa Yoshioka, Yusuke Arashida, Zi-Han Wang, Yasuyuki Sanari, Osamu Takeuchi, Yoshihiko Kanemitsu, Hidemi Shigekawa,

https://pubs.acs.org/doi/abs/10.1021/acsphotonics.9b00266

The recent development of optical technology has enabled the practical use of a carrier-envelope phase-controlled monocycle electric field in the terahertz (THz) regime. By combining this technique with metal nanostructures such as nanotips, which induce near-field enhancement, the development of novel applications is anticipated. In particular, THz scanning tunneling microscopy (THz-STM) is a promising technique for probing ultrafast dynamics with the spatial resolution of STM. However, the modulation of the THz waveform is generally accompanied by an enhancement of the electric field, which is unknown in actual measurement environments. Here, we present a method enabling direct evaluation of the enhanced near field in the tunnel junction in THz-STM in the femtosecond range, which is essential for the use of the THz near field. In the tunneling regime, it was also demonstrated that the transient electronic state excited by an optical pulse can be evaluated using the THz-STM, and the ultrafast carrier dynamics in 2H-MoTe2 excited by an optical pulse was reproducibly probed.

Abstract-Nonlinear terahertz dynamics of Dirac electrons in Bi thin films

Ikufumi Katayama, Yasuo Minami, Yusuke Arashida, Orjan Sele Handegard, Tadaaki Nagao, Masahiro Kitajima, Jun Takeda

https://www.spiedigitallibrary.org/conference-presentations/10756/107560P/Nonlinear-terahertz-dynamics-of-Dirac-electrons-in-Bi-thin-films/10.1117/12.2320801?contentType=Conference_Presentations&SSO=1&startYear=2018&endYear=2018&term=terahertz%7c%7c

By using both linear and nonlinear terahertz spectroscopy on epitaxial Bi and Bi1-xSbx thin films, we systematically investigated the linear and nonlinear terahertz dynamics of Dirac electrons. The linear terahertz transmittance was analyzed by the Drude model up to 50 THz, and then the plasma frequency and the damping constant were evaluated as functions of the film thickness and Sb-concentration. We found surface metallic state for Bi ultra-thin films, while semimetal to semiconductor crossover for Bi1-xSbx thin films. In the nonlinear terahertz spectroscopy, the terahertz transmittance increases with increasing the field strength, which could be assigned to the carrier acceleration along the Dirac-like band dispersion at the L point in the Brillouin zone. In addition, we observed the terahertz-induced absorption in terahertz-pump and terahertz-probe spectroscopy, which could be assigned to carrier generation due to Zener tunneling in Dirac band structure. The results demonstrate that Bi-related materials are promising candidates for future nonlinear terahertz devices.

© 2018 COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

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