Abstract-Terahertz vibrational signature of bacterial spores arising from nanostructure decorated endospore surface

Debopam Datta,   Michael A. Stroscio,   Mitra Dutta,   Weidong Zhang,   Elliott R. Brown,

https://onlinelibrary.wiley.com/doi/full/10.1002/jbio.201700398

This theoretical effort is the first to explore the possible hypothesis that terahertz optical activity of Bacillus spores arises from normal vibrational modes of spore coat subcomponents in the terahertz frequency range. Bacterial strains like Bacillus and Clostridium form spores with a hardened coating made of peptidoglycan to protect its genetic material in harsh conditions. In recent years, electron microscopy and atomic force microscopy has revealed that bacterial spore surfaces are decorated with nanocylinders and honeycomb nanostructures. In this article, a simple elastic continuum model is used to describe the vibration of these nanocylinders mainly in Bacillus subtilis, which also leads to the conclusion that the terahertz signature of these spores arises from the vibration of these nanostructures. Three vibrating modes: radial/longitudinal, torsional and flexural, have been identified and discussed for the nanocylinders. The effect of bound water, which shifts the vibration frequency, is also discussed. The peptidoglycan molecule consists of polar and charged amino acids; hence, the sporal surface local vibrations interact strongly with the terahertz radiation.

Abstract-Broadband impedance match to two-dimensional materials in the terahertz domain

Phi H. Q. Pham, Weidong Zhang, Nhi V. Quach, Jinfeng Li, Weiwei Zhou, Dominic Scarmardo, Elliott R. Brown & Peter J. Burke,

https://www.nature.com/articles/s41467-017-02336-z

The coupling of an electromagnetic plane wave to a thin conductor depends on the sheet conductance of the material: a poor conductor interacts weakly with the incoming light, allowing the majority of the radiation to pass; a good conductor also does not absorb, reflecting the wave almost entirely. For suspended films, the transition from transmitter to reflector occurs when the sheet resistance is approximately the characteristic impedance of free space (Z0 = 377 Ω). Near this point, the interaction is maximized, and the conductor absorbs strongly. Here we show that monolayer graphene, a tunable conductor, can be electrically modified to reach this transition, thereby achieving the maximum absorptive coupling across a broad range of frequencies in terahertz (THz) band. This property to be transparent or absorbing of an electromagnetic wave based on tunable electronic properties (rather than geometric structure) is expected to have numerous applications in mm wave and THz components and systems.

Abstract-High extinction ratio terahertz wire-grid polarizers with connecting bridges on quartz substrates

John S. Cetnar, Shivashankar Vangala, Weidong Zhang, Carl Pfeiffer, Elliott R. Brown, and Junpeng Guo

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-5-955&origin=search

A terahertz (THz) wire-grid polarizer with metallic bridges on a quartz substrate was simulated, fabricated, and tested. The device functions as a wide-band polarizer to incident THz radiation. In addition, the metallic bridges permit the device to function as a transparent electrode when a DC bias is applied to it. Three design variations of the polarizer with bridges and a polarizer without bridges were studied. Results show the devices with bridges have average 𝑠$s$-polarization transmittance of less than −3  dB$-3\mathrm{dB}$ and average extinction ratios of approximately 40 dB across a frequency range of 220–990 GHz and thus are comparable to a polarizer without bridges.

Abstract-High extinction ratio terahertz wire-grid polarizers with connecting bridges on quartz substrates

John S. Cetnar, Shivashankar Vangala, Weidong Zhang, Carl Pfeiffer, Elliott R. Brown, and Junpeng Guo

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-5-955

A terahertz (THz) wire-grid polarizer with metallic bridges on a quartz substrate was simulated, fabricated, and tested. The device functions as a wide-band polarizer to incident THz radiation. In addition, the metallic bridges permit the device to function as a transparent electrode when a DC bias is applied to it. Three design variations of the polarizer with bridges and a polarizer without bridges were studied. Results show the devices with bridges have average 𝑠$s$-polarization transmittance of less than −3  dB$-3\mathrm{dB}$ and average extinction ratios of approximately 40 dB across a frequency range of 220–990 GHz and thus are comparable to a polarizer without bridges.