Browsing by Author "Nordlander, Peter J"

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    Multiparticle Optical and Thermal Effects in Illuminated Solutions of Plasmonic Nanoparticles
    (2014-10-22) Hogan, Nathaniel J; Halas, Naomi J; Nordlander, Peter J; Hafner, Jason
    Plasmonic nanoparticles are found in a number of applications as efficient converters of optical energy into heat, e.g. cancer therapy of nanoparticle-laden tumors. More recently, aqueous solutions of plasmonic nanoparticles have proven the ability to produce steam with relatively high efficiencies upon solar illumination. We show in this report through modeling of the light transport in nanoparticle solutions that this effect originates in the optical properties of the nanoparticles. Strong optical scattering leads to multiparticle interactions that can concentrate light resulting in large temperature increases in the focused region. This model can be extended to all systems of dense nanoparticles in which light to heat conversion is crucial, e.g. photothermal cancer therapy and materials processing.
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    Nonlinear Nanophotonic Systems for Harmonic Generation, Parametric Amplification, Optical Processing and Single-Molecule Detection
    (2015-02-19) Zhang, Yu; Halas, Naomi J; Nordlander, Peter J; Link, Stephan
    Metallic nanoparticles support collective oscillations of conduction-band electrons, in response to light incidences. Such phenomenon is called localized surface plasmons, which confine large electromagnetic fields in sub-wavelength dimensions, enabling the light manipulation at the nanoscale. Plasmonic nanoparticles have established many promising applications, such as infrared photodetections, photothermal generation steam, chemical photocatalysis, cancer therapy and surface-enhanced spectroscopy. More interesting, plasmonic nanostructures could generate strong nonlinear-optical effects by relatively low excitation powers, and have been widely used in different processes like second-harmonic generations (SHG), difference-frequency generation (DFG), third-harmonic generation (THG), optical four-wave mixing (FWM) and surface-enhanced Raman scattering (SERS). This thesis will focused on two types of second-order and two types of third-order nonlinear-optical processes, enhanced by artificial plasmonic nanostructures. Firstly, the second-harmonic generation on a single nanocup is studied, and the signal is demonstrated to have increasing intensity as the 3D symmetry of the nanocup is reduced. Then, optical four-wave mixing is generated on a plasmonic nanocluster which supports a coherent oscillation of two Fano resonances. The electric fields from both Fano resonances add coherently resulting in strong fields and correspondingly large signals. This nanocluster has a large color-conversion efficiency, and could be used for building blocks of optical processors that convert two input colors into a third color. Later, one specific application of four-wave mixing, the coherent anti-Stokes Raman scattering (CARS) is studied. By exploiting the unique light harvesting properties of a Fano resonance of a specially designed nano-quadrumer, the surface-enhanced CARS (SECARS) technique amplifies the Raman signals of molecules on the quadrumer by about 100 billion times. This enables the accurate identification of a single molecule with less than 20 atoms. Finally, a plasmon-enhanced optical parametric amplifier (OPA) is designed: A BaTiO3 nanosphere is used as the nonlinear OPA medium; A nanoshell wrapping this nanosphere is used as a triply resonant cavity for all the pump, signal and idler beams; The generated idler beam has a wide tuning range in the near-infrared by changing the delay between the narrowband pump beam and broadband signal beam. This surface-plasmon-enhanced OPA could be an efficient light source working in the infrared regime, with large wavelength tunabilities and nanoscale dimensions easily integrated into the next-generation optoelectronic devices.
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    Single-particle absorption spectroscopy by photothermal contrast
    (2014-11-21) Nizzero, Sara; Link, Stephan; Landes, Christy F; Nordlander, Peter J; Kelly, Kevin F
    Independent characterization of absorption of nano-objects is fundamental to the understanding of non-radiative properties of light matter interaction. To resolve heterogeneity in the response due to local effects, orientation or rare interactions, a single particle approach is necessary. Currently, there are very few methods that attempt to do so. Furthermore, they are limited in the type of structures and the spectral range for which they succeed. This work presents the first general and broad band method to measure the pure absorption spectrum of single particles. Photothermal microscopy is combined with a supercontinuum pulsed fiber optic tunable laser to detect a signal proportional to the pure absorption cross section of single particles at different excitation wavelengths. For the first time, a method is available to measure the pure absorption spectra of single nano-structures that exhibit spectral features from the visible to the near IR. This method is used to resolve the radiative and non-radiative properties of simple gold nanostructures, revealing the heterogeneity present in the response.