Geometric phase diffractive optics technology is rapidly advancing including patterned liquid crystal and polymer liquid crystal elements and devices. The need exists for a set of design methods and tools to engineer optical components and systems. Numerical and analytical design methods are discussed with an emphasis on optical systems. Multilevel simulation methods are used incorporating full numerical electromagnetic solutions, diffraction theory, and ray tracing. Additionally, iterative algorithms are used to design the local anisotropic axis orientation of various regions in order to produce the desired diffraction effects. Elements are optimized for both amplitude and phase. Examples are presented including an optical system based on geometric phase elements that sorts the orbital and spin angular momentum states of an optical beam. Designs are demonstrated in polymer liquid crystal diffractive waveplate thin film elements fabricated through photo-alignment with a spatial light polarization modulator. The array of numerical design technique presented allow the rapid design of optical phase patterns, integration with real optical systems, and evaluation of physical materials and device properties.
Light emission from metal nanoparticles has potential appications as a highly sensitive refractive index detector. In order for this protential to be realized the mechanics of plasmon enhanced photoluminescence (PL) in planar nanoparticle arrays must be understude. We present an experimental exploreation of emission spectra and realitive efficiency of gold PL in nanoplasmonic arrays. We demonstrate tunability of metal PL by nanoparticle size and discover the critical role of near-field interparticle coupling on emission efficiency. We show that direct excition of plasmon resonances by photoexcited electron-hole pairs is the primary contributer to the metalic nanoparticle emission spectrum. We additionally show that emission is quenched by near-field interactions between nanoparticles leading to spectral broading by increased non-radiative plasmon decay. Finally, we show a correlation between plasmon life-time and PL efficiency. We explore this phenominan for both linear and nonlinear PL. Experimental results are supported by numerical simulations of plasmon life-time.
Scattering by plasmon resonances of metallic nanoparticles can be tailored by particle material, size, shape, and local as well as long-range order. In this presentation we discuss a series of experiments in which long-range Fano-type coupling between grating resonances and localized surface palsmon (LSP) resonances were studied using second harmonic excitation (SH-E) spectroscopy. By tuning the excitation wavelength of a femtosecond laser and measuring the relative second harmonic (SH) signal we demonstrated that when long-range grating resonances spectrally overlap with those of the LSPs, electromagnetic field enhancement occurs on the surface of the nanoparticles leading to an increase in nonlinear scattering. This effect has been demonstrated for periodic arrays of monomers and dimers, bi-periodic antenna arrays for multi-spectral focusing to a single point, and chirped nanoparticle structures for broadband field enhancement. Results are supported by finite difference time domain simulations showing that electromagnetic fields are enhanced close on the surface of the nanoparticles when long-range structural resonances are excited. These studies have revealed design principles for engineering the interplay of photonic and plasmonic coupling for future linear and nonlinear plasmonic devices.
The ability to reproducibly and accurately control light matter interaction on the nanoscale is at the core of the field of
optical biosensing enabled by the engineering of nanophotonic and nanoplasmonic structures. Efficient schemes for
electromagnetic field localization and enhancement over precisely defined sub-wavelength spatial regions is essential to
truly benefit from these emerging technologies. In particular, the engineering of deterministic media without translational
invariance offers an almost unexplored potential for the manipulation of optical states with vastly tunable transport and
localization properties over broadband frequency spectra. In this paper, we discuss deterministic aperiodic plasmonic and
photonic nanostructures for optical biosensing applications based on fingerprinting Surface Enhanced Raman Scattering
(SERS) in metal nanoparticle arrays and engineered light scattering from nanostructured dielectric surfaces with low
refractive index (quartz).
Frequency Selective Surfaces (FSS) are comprised of periodic, geometric, metallic patterns that act like an array of horizontal antennas. They were originally designed as band-pass/band-block filters. Nanofabrication techniques allow for the realization of FSS structures that operate in the near infrared (NIR) and visible portions of the electromagnetic spectrum. Thus it is possible to create arrays of light antenna filters possessing optical properties that are unlike those of dye, dielectric, or holographic filters that are in common use today. Recent studies of arrays of gold, dipole
nanoantennas by our group and others offer an opportunity to compare modeled FSS response with experimental results elucidating the unique, off-normal reflectance stability of frequency selective surfaces operating in the NIR/visible portion of the spectrum.
Carbon nanotubes have been shown to exhibit light antenna behavior, such as polarization and length dependence,
and enhancement of incident electromagnetic radiation at resonance. We study and model resonance effects from
planar metallic nanoantennas, as a function of nanoantenna dimensions and material properties. We discuss the
challenges of designing a two-dimensional nanoantenna array with resonance in the short wavelength (blue-green)
region of the visible spectrum, constructed from different materials and in different environments.
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