arXiv subjects
Publications and source records attributed to Jake Fontana.
We report the dynamics and control of the orientational and positional order of ensembles of gold nanorods suspended in air at standard temperature and pressure using externally applied electric fields, demonstrating an active aerosol. Light filter, valve and gradient responses are shown, establishing active aerosols as a unique type of optical element we term component-less optics.
Powerful rogue ocean waves have been objects of fascination for centuries. Elusive and awe-inspiring, with the ability to inflict catastrophic damage, rogue waves remain unpredictable and imperfectly understood. To gain further insight into their behavior, we analyzed 3,441,188,683 ocean surface waves in order to determine the statistical height distribution of the largest waves. We found that the distribution of rare events which resolves the St. Petersburg paradox also describes the relative height distribution of the largest waves. This result will contribute to the modeling of ocean surface dynamics and improve the accuracy of marine weather forecasts.
The St. Petersburg paradox provides a simple paradigm for systems that show sensitivity to rare events. Here, we demonstrate a physical realization of this paradox using tensile fracture, experimentally verifying for six decades of spatial and temporal data and two different materials that the fracture force depends logarithmically on the length of the fiber. The St. Petersburg model may be useful in a variety fields where failure and reliability are critical.
Plasmonic nanoparticles resonantly couple to and confine light below the diffraction limit. This mechanism has enabled a modern renaissance in optical materials, with potential applications ranging from sensing and circuitry to renewable energies and medicines. However, these plasmonic materials are typically constrained to dilute liquids or solid two-dimensional surfaces, thereby limiting their possibilities. Here, we experimentally demonstrate a plasmonic aerosol by transitioning liquid suspensions of gold nanorods into the gas phase and simultaneously measuring their optical spectra. By measuring and modeling the evolution of the longitudinal absorbance peak of the nanorods from the liquid to the gas phase, we find that the aerosols are optically homogeneous and thermodynamically stable. We show that by tailoring the aspect ratio of the nanorods, the aerosol absorbance peak is tunable from visible to mid-wave infrared wavelengths. We find the sensitivity of the absorbance peak wavelength to changes in the refractive index of the gas depends linearly on the aspect ratio and can be estimated from the geometric and material properties of the nanorod. For high aspect ratio nanorods the sensitivity becomes extremely large, which may be useful in aiding geoengineering challenges. This work establishes plasmonic aerosols, potentially enabling exciting opportunities for fundamental and applied research.
The capability to dynamically control the nonlinear refractive index of plasmonic suspensions may enable innovative nonlinear sensing and signaling nanotechnologies. Here, we experimentally determine the effective nonlinear refractive index for gold nanorods suspended in an index matching oil aligned using electric fields, demonstrating an approach to modulate the nonlinear optical properties of the suspension. The nonlinear optical experiments were carried out using a Hartmann-Shack wavefront aberrometer in a collimated beam configuration with a high repetition rate femtosecond laser. The suspensions were probed at 800 nm, overlapping with the long-axis absorption peak of the nanorods. We find that the effective nonlinear refractive index of the gold nanorods suspension depends linearly on the orientational order parameter, S, which can be understood by a thermally induced nonlinear response. We also show the magnitude of the nonlinear response can be varied by ~60%.
We demonstrate the digital electric field induced switching of plasmonic nanorods between 1 and 0 orthogonal aligned states using an electro-optic fluid fiber component. We show by digitally switching the nanorods, that thermal rotational diffusion of the nanorods can be circumvented, demonstrating an approach to achieve submicrosecond switching times. We also show, from an initial unaligned state, that the nanorods can be aligned into the applied electric field direction in 110 nanoseconds. The high-speed digital switching of plasmonic nanorods integrated into an all-fiber optical component may provide novel opportunities for remote sensing and signaling applications.
The index of refraction governs the flow of light through materials. At visible and near infrared wavelengths the real part of the refractive index is limited to less than 3 for naturally occurring transparent materials, fundamentally restricting applications. Here, we carried out experiments to study the upper limit of the effective refractive index of self-assembled metasurfaces at visible and near-infrared wavelengths. The centimeter-scale metasurfaces were made of a hexagonally close packed (hcp) monolayer of gold nanospheres coated with tunable alkanethiol ligand shells, controlling the interparticle gap from 2.8 to 0.45 nm. In contrast to isolated dimer studies, the macro-scale areas allow for billions of gaps to be simultaneously probed and the hcp symmetry leads to large wavelength shifts in the resonance mode, enabling subnanometer length scale mechanisms to be reproducibly measured in the far-field. We demonstrate for subnanometer gaps, that the optical response of the metasurfaces agrees well with a classical (local) model, with minor nonlocal effects and no clear evidence of ligand-mediated charge transfer at optical frequencies. We determine the effective real part of the refractive index for the metasurfaces has a minimum of 1.0 for green-yellow colors, then quickly reaches a maximum of 5.0 in the reds and remains larger than 3.5 far into the near infrared. We further show changing the terminal group and conjugation of the ligands in the metasurfaces has little effect on the optical properties. These results establish a pragmatic upper bound on the confinement of visible and near infrared light, potentially leading to unique dispersion engineered coatings