Surface Plasmon polaritons have long been utilized to enhance and confine optical fields at the nanoscale. They have been proven effective in the control and enhancement of optical processes at metal-dielectric boundaries with a variety of applications including nonlinear optics. In this paper we review the application of plasmonic metasurfaces to enhance non-linear processes on semiconductors, crystals, 2-D materials (graphene) and in the metal itself forming the metasurface. We consider applications such as harmonic generation, the generation of vortex beams, and the enhancement of nonlinear processes in 2D materials (graphene).
The use of metal nanostructures to produce colour has recently attracted a great deal of interest. This interest is motivated by colours that can last a long time and that can be rendered down to the diffraction limit, and by processes that avoid the use of inks, paints or pigments for environmental, health or other reasons. The central idea consists of forming metal nanostructures which exhibit plasmon resonances in the visible such that the spectrum of reflected light renders a desired colour. We describe a single-step laser-writing process that produces a full palette of colours on bulk metal objects. The colours are rendered through spectral subtraction of incident white light. Surface plasmons on networks of metal nanoparticles created by laser ablation play a central role in the colour rendition. The plasmonic nature of the colours are studied via large-scale finite-difference time-domain simulations based on the statistical analysis of the nanoparticle distribution. The process is demonstrated on Ag, Au, Cu and Al surfaces, and on minted Ag coins targeting the collectibles market. We also discuss the use of these coloured surfaces in plasmonic assisted photochemistry and their passivation for day-to-day use. Reactions on silver that are normally driven by UV light exposure are demonstrated to occur in the visible spectrum.
We show the angle-independent coloring of metals in air arising from nanoparticle distributions on metal surfaces created via picosecond laser processing. Each of the colors is linked to a unique total accumulated fluence, rendering the process compatible with industry. We report the coating of the colored metal surfaces using atomic layer deposition which is shown to preserve colors and provide mechanical and chemical protection Laser bursts are composed of closely time-spaced pulses separated by 12.8 ns. The coloring of silver using burst versus non-burst is shown to increase the Chroma, or color saturation, by 50% and broaden the color Lightness range by up to 60%. The increase in Chroma and Lightness are accompanied by the creation of 3 kinds of different laser-induced periodic surface structures (LIPSS). One of these structures is measured to be 10 times the wavelength of light and are not yet explained by conventional theories. Two temperature model simulations of laser bursts interacting with the metal surface show a significant increase in the electron-phonon coupling responsible for the well-defined LIPSS observed on the surface of silver. Finite-difference time-domain simulations of nanoparticles distributed on the high-spatial frequency LIPSS (HSFL) explain the increase in color saturation (i.e. Chroma of the colors) by the enhanced absorption and enriched plasmon resonances.
This work describes a computational approach for the optical characterization of an opal photonic crystal (PC). We intend, in particular, to validate our approach by comparing the transmittance of a crystal model, as obtained by numerical simulation, with the transmittance of the same crystal, as measured over 400- to 700-nm wavelength range. We consider an opal PC with a face-centered cubic lattice structure of spherical particles made of polystyrene (a nonabsorptive material with constant relative dielectric permittivity). Light-crystal interaction is simulated by numerically solving Maxwell’s equations via the finite-difference time-domain method and by using the Kirchhoff formula to calculate the far field. A method to study the propagating Bloch modes inside the crystal bulk is also sketched.
Hyperspectral coherent anti-Stokes Raman scattering (CARS) microscopy has provided an imaging tool for
extraction of 3-dimensional volumetric information, as well as chemically-sensitive spectral information. These
techniques have been used in a variety of different domains including biophysics, geology, and material science.
The measured CARS spectrum results from interference between the Raman response of the sample and a non-resonant
background. We have collected four dimensional data sets (three spatial dimensions, plus spectra)
and extracted Raman response from the CARS spectrum using a Kramers-Kronig transformation. However,
the three dimensional images formed by a CARS microscope are distorted by interference, some of which arises
because of the Gouy phase shift. This type of interference comes from the axial position of the Raman resonant
object in the laser focus. We studied how the Gouy phase manifests itself in the spectral domain by investigating
microscopic diamonds and nitrobenzene droplets in a CARS microscope. Through experimental results and
numerical calculation using finite-diference time-domain (FDTD) methods, we were able to demonstrate the
relationship between the spatial configuration of the sample and the CARS spectral response in three dimensional
Optical scattering loss in sub-micron scale patterned waveguides is one of the most important physical mechanisms dictating the limitations and applications of optical devices containing such structures. Despite this,there has been little theoretical work describing the extrinsic scattering losses in photonic crystal waveguides due to random fabrication variations such as disorder and surface roughness. While much work has been devoted to the characterization of ideal, lossless photonic crystal devices, the role of extrinsic optical scattering loss has not yet been suitably addressed. We present explicit formulas that describe extrinsic optical scattering loss for arbitrary sub-micron patterned waveguides occuring due fabricated imperfections such as disorder and surface roughness. Using a real-space Green function formalism, we derive original expressions for the backscattered loss and the total transmission loss, including out-of-plane contributions. Numerical calculations for planar photonic crystal waveguides yield extrinsic loss values in overall agreement with experimental measurements reported in the literature. Additionally, our formulas offer physical insight, including scaling rules that indicate how waveguide losses may be reduced by improved design. In particular, we highlight that loss becomes unavoidably large for operating frequencies approaching the photonic bandedge.