Abstract-Quantitative terahertz emission nanoscopy with multiresonant near-field probes

 

Fabian Mooshammer, Markus Plankl, Thomas Siday, Martin Zizlsperger, Fabian Sandner, Rocco Vitalone, Ran Jing, Markus A. Huber, D. N. Basov, and Rupert Huber

https://www.osapublishing.org/viewmedia.cfm?r=1&rwjcode=ol&uri=ol-46-15-3572&seq=0

By sampling terahertz waveforms emitted from InAs surfaces, we reveal how the entire, realistic geometry of typical near-field probes drastically impacts the broadband electromagnetic fields. In the time domain, these modifications manifest as a shift in the carrier-envelope phase and emergence of a replica pulse with a time delay dictated by the length of the cantilever. This interpretation is fully corroborated by quantitative simulations of terahertz emission nanoscopy based on the finite element method. Our approach provides a solid theoretical framework for quantitative nanospectroscopy and sets the stage for a reliable description of subcycle, near-field microscopy at terahertz frequencies.

© 2021 Optical Society of America

Abstract-Terahertz Detection with Perfectly-Absorbing Photoconductive Metasurface

Thomas Siday,  Polina Vabishchevich, Lucy Hale, Charles Harris, Shan Ting Shan, John Reno, Igal Brener, Oleg Mitrofanov,

https://www.osti.gov/pages/biblio/1515200

Terahertz (THz) photoconductive devices are utilized for generation, detection, and modulation of THz waves, and they rely on the ability to switch electrical conductivity on a subpicosecond time scale using optical pulses. Yet, fast and efficient conductivity switching with high contrast has been a challenge, because the majority of photoexcited charge carriers in the switch do not contribute to the photocurrent due to fast recombination. Here, we improve efficiency of electrical conductivity switching using a network of electrically connected nanoscale GaAs resonators, which form a perfectly absorbing photoconductive metasurface. We achieve perfect absorption without incorporating metallic elements, by breaking the symmetry of cubic Mie resonators. As a result, the metasurface can be switched between conductive and resistive states with extremely high contrast using an unprecedentedly low level of optical excitation. We integrate this metasurface with a THz antenna to produce an efficient photoconductive THz detector. The perfectly absorbing photoconductive metasurface opens paths for developing a wide range of efficient optoelectronic devices, where required optical and electronic properties are achieved through nanostructuring the resonator network.

Abstract-Resonant terahertz probes for near-field scattering microscopy

Thomas Siday, Michele Natrella, Jiang Wu, Huiyun Liu, and Oleg Mitrofanov

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-22-27874


We propose and characterize a scattering probe for terahertz (THz) near-field microscopy, fabricated from indium, where the scattering efficiency is enhanced by the dipolar resonance supported by the indium probe. The scattering properties of the probe were evaluated experimentally using THz time-domain spectroscopy (TDS), and numerically using the finite-difference time-domain (FDTD) method in order to identify resonant enhancement. Numerical measurements show that the indium probes exhibit enhanced scattering across the THz frequency range due to dipolar resonance, with a fractional bandwidth of 0.65 at 1.24 THz. We experimentally observe the resonant enhancement of the scattered field with a peak at 0.3 THz. To enable practical THz microscopy applications of these resonant probes, we also demonstrate a simple excitation scheme utilizing a THz source with radial polarization, which excites a radial mode along the length of the tip. Strong field confinement at the apex of the tip, as required for THz near-field microscopy, was observed experimentally.

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