Roderick B. Davidson

Efficient forward second-harmonic generation from planar archimedean nanospirals

Abstract: The enhanced electric field at plasmonic resonances in nanoscale antennas can lead to efficient harmonic generation, especially when the plasmonic geometry is asymmetric on either inter-particle or intra-particle levels. The planar Archimedean nanospiral offers a unique geometrical asymmetry for second-harmonic generation (SHG) because the SHG results neither from arranging centrosymmetric nanoparticles in asymmetric groupings, nor from non-centrosymmetric nanoparticles that retain a local axis of symmetry. Here, we report forward SHG from planar arrays of Archimedean nanospirals using 15 fs pulses from a Ti:sapphire oscillator tuned to 800 nm wavelength. The measured harmonic-generation efficiencies are 2.6·10−9, 8·10−9 and 1.3·10−8 for left-handed circular, linear, and right-handed circular polarizations, respectively. The uncoated nanospirals are stable under average power loading of as much as 300 μWper nanoparticle. The nanospirals also exhibit selective conversion between polarization states. These experiments show that the intrinsic asymmetry of the nanospirals results in a highly efficient, two-dimensional harmonic generator that can be incorporated into metasurface optics.

Unveiling Complex Plasmonic Resonances in Archimedean Nanospirals through Cathodoluminescence in a Scanning Transmission Electron Microscope

Metallic nanostructures with a complex plasmonic response, such as the Archimedean nanospiral (ANS) present novel ways to utilize plasmonics in modern technology [1,2]. The nanospiral can support several resonant modes, with distinct electric field profiles as shown by finite-difference time-domain (FDTD) simulations such as the hourglass (500-650nm) and focusing (650-980nm) modes [2]. In addition to the linear plasmonic response, the ANS exhibits a stronger second-order nonlinearity than seen in other metallic nanostructured systems. A high spatial-resolution picture of the plasmonic modes is critical to understanding the interactions between plasmonic modes that drive the high non-linear efficiencies [3].

Polarization- and wavelength-resolved near-field imaging of complex plasmonic modes in Archimedean nanospirals

Asymmetric nanophotonic structures enable a wide range of opportunities in optical nanotechnology because they support efficient optical nonlinearities mediated by multiple plasmon resonances over a broad spectral range. The Archimedean nanospiral is a canonical example of a chiral plasmonic structure because it supports even-order nonlinearities that are not generally accessible in locally symmetric geometries. However, the complex spiral response makes nanoscale experimental characterization of the plasmonic near-field structure highly desirable. Here we employ high-efficiency, high-spatial-resolution cathodoluminescence imaging in a scanning transmission electron microscope to describe the spatial, spectral, and polarization response of plasmon modes in the nanospiral geometry.

Ultrafast Transmission Modulation and Recovery via Vibrational Strong Coupling

Strong coupling between vibrational modes and cavity optical modes leads to the formation of vibration-cavity polaritons, separated by the vacuum Rabi splitting. The splitting depends on the square root of the concentration of absorbers confined in the cavity, which has important implications on the response of the coupled system after ultrafast infrared excitation. In this work, we report on solutions of W(CO)6 in hexane with a concentration chosen to access a regime that borders on weak coupling. Under these conditions, large fractions of the W(CO)6 oscillators can be excited, and the anharmonicity of the molecules leads to a commensurate reduction in the Rabi splitting. We report excitation fractions > 0.4, depending on excitation pulse intensity, and show drastic increases in transmission that can be modulated on the picosecond time scale. In comparison to previous experiments, the transient spectra that we observe are much simpler because excited-state transitions lie outside of the transmission spectrum of the cavity, thereby contributing only weakly to the spectra. We find that the Rabi splitting recovers with the characteristic vibrational relaxation lifetime and anisotropy decay of uncoupled W(CO)6, implying that polaritons are not directly involved in the relaxation we observe after the first few ps. The results help corroborate the model that we proposed to describe the results at higher concentrations and show that the ground-state bleach of cavity-coupled molecules has a broad, multisigned spectral response.

Transduction of Entangled Images by Localized Surface Plasmons

We demonstrate the transduction of entangled images through independent plasmonic structures. The results show that both entanglement and spatial properties are preserved and allow us to infer the transfer of entanglement between light and plasmons.

Near-Field Mid-Infrared Plasmonics in Complex Nanostructures with Monochromated Electron Energy Loss Spectroscopy

1. Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN USA 2. Chemical Division, Naval Research Laboratory, Annapolis, MD USA 3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN USA 4. Department of Physics and Astronomy, Vanderbilt University, Nashville, TN USA 5. Department of Electrical Engineering & Computer Science, Vanderbilt University Nashville, TN USA 6. Computational Sciences & Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN USA

Observing Nanoscale Orbital Angular Momentum in Plasmon Vortices with Cathodoluminescence

1. Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, TN USA 2. Klipsch School of Electrical & Computer Engineering, New Mexico State University, Las Cruces, NM USA 3. Chemical Division, Naval Research Laboratory, Annapolis, MD USA 4. Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN USA 5. Department of Physics & Astronomy, Vanderbilt University, Nashville, TN USA 6. Department of Electrical Engineering & Computer Science, Vanderbilt University Nashville, TN USA 7. Computational Sciences & Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN USA

All-optical-field-induced second-harmonic generation

Interferometric pump-probe spectroscopy is used to demonstrate all-optical second-harmonic generation from a polymer dielectric in a serrated nanogap structure. Strong optical frequency electric-fields from surface plasmons create ultrafast controllable nonlinear light pulses.

Efficient forward second-harmonic generationfrom planar archimedean nanospirals

Abstract: The enhanced electric field at plasmonic resonances in nanoscale antennas can lead to efficient harmonic generation, especially when the plasmonic geometry is asymmetric on either inter-particle or intra-particle levels. The planar Archimedean nanospiral offers a unique geometrical asymmetry for second-harmonic generation (SHG) because the SHG results neither from arranging centrosymmetric nanoparticles in asymmetric groupings, nor from non-centrosymmetric nanoparticles that retain a local axis of symmetry. Here, we report forward SHG from planar arrays of Archimedean nanospirals using 15 fs pulses from a Ti:sapphire oscillator tuned to 800 nm wavelength. The measured harmonic-generation efficiencies are 2.6·10−9, 8·10−9 and 1.3·10−8 for left-handed circular, linear, and right-handed circular polarizations, respectively. The uncoated nanospirals are stable under average power loading of as much as 300 μWper nanoparticle. The nanospirals also exhibit selective conversion between polarization states. These experiments show that the intrinsic asymmetry of the nanospirals results in a highly efficient, two-dimensional harmonic generator that can be incorporated into metasurface optics.

Eflcient forward second-harmonic generationfrom planar archimedean nanospirals

Abstract: The enhanced electric field at plasmonic resonances in nanoscale antennas can lead to efficient harmonic generation, especially when the plasmonic geometry is asymmetric on either inter-particle or intra-particle levels. The planar Archimedean nanospiral offers a unique geometrical asymmetry for second-harmonic generation (SHG) because the SHG results neither from arranging centrosymmetric nanoparticles in asymmetric groupings, nor from non-centrosymmetric nanoparticles that retain a local axis of symmetry. Here, we report forward SHG from planar arrays of Archimedean nanospirals using 15 fs pulses from a Ti:sapphire oscillator tuned to 800 nm wavelength. The measured harmonic-generation efficiencies are 2.6·10−9, 8·10−9 and 1.3·10−8 for left-handed circular, linear, and right-handed circular polarizations, respectively. The uncoated nanospirals are stable under average power loading of as much as 300 μWper nanoparticle. The nanospirals also exhibit selective conversion between polarization states. These experiments show that the intrinsic asymmetry of the nanospirals results in a highly efficient, two-dimensional harmonic generator that can be incorporated into metasurface optics.