Abstract-Dewetting during Terahertz Vibrations of Nanoparticles

Ching-Chung Hsueh, Reuven Gordon, Joerg Rottler

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b03984?journalCode=nalefd

We use molecular simulations to demonstrate the formation of a vacuum layer around a vibrating nanoparticle in a liquid. This vacuum layer forms readily for high frequencies with respect to the Einstein frequency of the fluid, even with small amplitude vibrations. The opposite is true for low frequencies, where large amplitudes are required to demonstrate the vacuum layer. With the vacuum layer forming, the quality factor of the oscillations increases substantially. The findings provide an interpretation of our recent experiments that show the onset of high-quality resonances of nanoparticles in water [Xiang et al., Nano Letters 16, 3638 (2016)] in the GHz to THz range.

Abstract-Plasmon-enhanced LT-GaAs/AlAs heterostructure photoconductive antennas for sub-bandgap terahertz generation

Afshin Jooshesh, Faezeh Fesharaki, Vahid Bahrami-Yekta, Mahsa Mahtab, Thomas Tiedje, Thomas E. Darcie, and Reuven Gordon

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-18-22140

Photocurrent generation in low-temperature-grown GaAs (LT-GaAs) has been significantly improved by growing a thin AlAs isolation layer between the LT-GaAs layer and semi-insulating (SI)-GaAs substrate. The AlAs layer allows greater arsenic incorporation into the LT-GaAs layer, prevents current diffusion into the GaAs substrate, and provides optical back-reflection that enhances below bandgap terahertz generation. Our plasmon-enhanced LT-GaAs/AlAs photoconductive antennas provide 4.5 THz bandwidth and 75 dB signal-to-noise ratio (SNR) under 50 mW of 1570 nm excitation, whereas the structure without the AlAs layer gives 3 THz bandwidth, 65 dB SNR for the same conditions.

© 2017 Optical Society of America

Abstract-Plasmonic Antireflection Coating for Photoconductive Terahertz Generation

Faezeh Fesharaki, Afshin Jooshesh, Vahid Bahrami-Yekta, Mahsa Mahtab, Tom Tiedje, Thomas E. Darcie, Reuven Gordon

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00410

Plasmon-enhanced photoconductive antennas allow for improved performance, particularly in below-band-gap absorption devices using low-temperature-grown GaAs. Here we design the plasmonic nanostructures to act as antireflection coatings as well, achieving below 10% reflection at 1570 nm wavelength in an optimized device. Quantitative agreement is seen between experiment and theory. Terahertz emission field amplitudes demonstrate 18 times enhancement compared to that of a conventional terahertz photoconductive antenna on the same substrate.

Abstract-Plasmonic Anti-reflection Coating for Photoconductive Terahertz Generation

Faezeh Fesharaki, Afshin Jooshesh, Vahid Bahrami-Yekta, Mahsa Mahtab, Tom Tiedje, Thomas E. Darcie, and Reuven Gordon

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00410?journalCode=apchd5

Plasmon-enhanced photoconductive antennas allow for improved performance, particularly in below-bandgap absorption devices using low-temperature grown GaAs. Here we design the plasmonic nanostructures to act as anti-reflection coatings as well, achieving below 10% reflection at 1570 nm wavelength in an optimized device. Quantitative agreement is seen between experiment and theory. Terahertz emission field amplitudes demonstrate eighteen times enhancement compared to that of a conventional terahertz photoconductive antenna on the same substrate.

Abstract-Threshold for Terahertz Resonance of Nanoparticles in Water

Dao Xiang, Jian Wu, Joerg Rottler, and Reuven Gordon

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.6b00770

Publication Date (Web): May 20, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b00770?journalCode=nalefd

Nanoparticle vibrations are coupled to light through electrostriction, which gives nonlinear optical scattering. We investigated the acoustic response of 2 nm gold nanoparticles using nearly-degenerate four-wave mixing experimental configuration and show that the nonlinear response suddenly turns on at low powers (<100 mW) for continuous-wave (CW) lasers. The observed nonlinear response is a million times larger than typical electronic nonlinearities. The threshold implies a dramatic change in the quality factor of the vibrating nanoparticles, 4 orders of magnitude larger than usual hydrodynamic theory predicts. It is as if the water is removed altogether, which we speculate is the result of the vibrating particle pushing away the water molecules to form a stable cavity. Since these acoustic vibrations extend to terahertz frequencies, there is potential to harness this effect for high speed optical data processing; as well as to probe the dynamics of proteins all having acoustic modes in this range.

Abstract-Plasmon-Enhanced below Bandgap Photoconductive Terahertz Generation and Detection

Afshin Jooshesh, Vahid Bahrami-Yekta, Jinye Zhang, Thomas Tiedje, Thomas E. Darcie, andReuven Gordon*

Department of Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia V8P 5C2, Canada

Nano Lett., Article ASAP

DOI: 10.1021/acs.nanolett.5b03922

Publication Date (Web): November 17, 2015

Copyright © 2015 American Chemical Society

*E-mail: rgordon@uvic.ca.

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b03922

We use plasmon enhancement to achieve terahertz (THz) photoconductive switches that combine the benefits of low-temperature grown GaAs with mature 1.5 μm femtosecond lasers operating below the bandgap. These below bandgap plasmon-enhanced photoconductive receivers and sources significantly outperform commercial devices based on InGaAs, both in terms of bandwidth and power, even though they operate well below saturation. This paves the way for high-performance low-cost portable systems to enable emerging THz applications in spectroscopy, security, medical imaging, and communication.

Abstract-Nanoplasmonics enhanced terahertz sources

Afshin Jooshesh, Levi Smith, Mostafa Masnadi-Shirazi, Vahid Bahrami-Yekta, Thomas Tiedje, Thomas E. Darcie, and Reuven Gordon  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-23-27992

Optics Express, Vol. 22, Issue 23, pp. 27992-28001 (2014)
http://dx.doi.org/10.1364/OE.22.027992

Arrayed hexagonal metal nanostructures are used to maximize the local current density while providing effective thermal management at the nanoscale, thereby allowing for increased emission from photoconductive terahertz (THz) sources. The THz emission field amplitude was increased by 60% above that of a commercial THz photoconductive antenna, even though the hexagonal nanostructured device had 75% of the bias voltage. The arrayed hexagonal outperforms our previously investigated strip array nanoplasmonic structure by providing stronger localization of the current density near the metal surface with an operating bandwidth of 2.6 THz. This approach is promising to achieve efficient THz sources.

© 2014 Optical Society of America

Abstract-Nanoplasmonic Terahertz Photoconductive Switch on GaAs

Barmak Heshmat , Hamid Pahlevaninezhad , Yuanjie Pang , Mostafa Masnadi Shirazi , Ryan B. Lewis , Thomas Tiedje , Reuven Gordon , and Thomas E. Darcie
http://pubs.acs.org/doi/abs/10.1021/nl303314a
Low-temperature (LT) grown GaAs has a sub-picosecond carrier response time that makes it favorable for terahertz photoconductive (PC) switching. However, this is obtained at the price of lower mobility and lower thermal conductivity than GaAs. Here we demonstrate sub-picosecond carrier sweep-out and over an order of magnitude higher sensitivity in detection from a GaAs-based PC switch by using a nanoplasmonic structure. As compared to a conventional GaAs PC switch, we observe 40 times the peak-to-peak response from the nanoplasmonic structure on GaAs. The response is double that of a commercial, antireflection coated LT-GaAs PC switch.