Railing Chang

High-resolution angular measurement using surface-plasmon-resonance via phase interrogation at optimal incident wavelengths

It is demonstrated that ultrahigh-resolution angular measurement can be achieved via surface-plasmon-resonance excitation in which the phase difference between p- and s-polarized reflected waves is monitored as a function of the incidence angle. Resolutions down to 1.9 x 10(-6) deg are obtained by performing the measurements at optimal incident wavelengths. This represents an order of magnitude improvement compared with previously reported values.

Imaging layer number and stacking order through formulating Raman fingerprints obtained from hexagonal single crystals of few layer graphene

Quantitative mapping of layer number and stacking order for CVD-grown graphene layers is realized by formulating Raman fingerprints obtained on two stepwise stacked graphene single-crystal domains with AB Bernal and turbostratic stacking (with ~30°interlayer rotation), respectively. The integrated peak area ratio of the G band to the Si band, A(G)/A(Si), is proven to be a good fingerprint for layer number determination, while the area ratio of the 2D and G bands, A(2D)/A(G), is shown to differentiate effectively between the two different stacking orders. The two fingerprints are well formulated and resolve, quantitatively, the layer number and stacking type of various graphene domains that used to rely on tedious transmission electron microscopy for structural analysis. The approach is also noticeable in easy discrimination of the turbostratic graphene region (~30° rotation), the structure of which resembles the well known high-mobility graphene R30/R2(±) fault pairs found on the vacuum-annealed C-face SiC and suggests an electron mobility reaching 14,700 cm(3) V(-1) s(-1). The methodology may shed light on monitoring and control of high-quality graphene growth, and thereby facilitate future mass production of potential high-speed graphene applications.

Nonlocal and nonlinear effects on the dispersion relation for surface plasmon at a metal-Kerr medium interface

By using the method of first integral, we theoretically study the dispersion relation of the surface plasmon at the metal-Kerr medium interface, with nonlocal effect of the metal taken into account.

Adjustable negative group-velocity dispersion in graded-index lenses.

An analysis of group-velocity dispersion in graded-index (GRIN) lenses is presented. The analysis shows that continuously adjustable negative group-velocity dispersion up to hundreds of square femtoseconds can be produced by propagating the optical beam off the axis of a GRIN lens. Compared with the well-known prism-pair and grating-pair methods for producing negative dispersion, the method described here is advantageous because it is 100-fold smaller, it has low insertion loss, and it is compatible with integrated optics.

Förster Resonance Energy Transfer Between Molecules in the Vicinity of Graphene-Coated Nanoparticles

The recent demonstration of the plasmonic-enhanced Förster resonance energy transfer (FRET) between two molecules in the vicinity of planar graphene monolayers is further investigated using graphene-coated nanoparticles (GNP). Due to the flexibility of these nanostructures in terms of their geometric (size) and dielectric (e.g., core material) properties, greater tunability of the FRET enhancement can be achieved employing the localized surface plasmons. It is found that while the typical characteristic graphene plasmonic enhancements are manifested from using these GNPs, even higher enhancements can be possible via doping and manipulating the core materials. In addition, the broadband characteristics are further expanded by the closely spaced multipolar plasmon resonances of the GNPs.

Optical interactions with a charged metallic nanoshell

The effect of extraneous charge on the optical interactions with metallic nanoshells is studied theoretically based on an effective medium model, with the electrodynamic theory also formulated to justify the accuracy of this model. Both optical far-field and near-field interactions will be studied. Furthermore, the hybridization model is generalized to include the charge effects yielding results for the multipole resonances consistent with those from the effective medium model. It is found that while the extraneous charges will lead to blueshifted resonances, their effect on the bonding modes will be most significant, especially for localized near-field sources. In addition, it is pointed out that the applicability of our theory can go beyond the metallic nanoshell to include graphene-coated core–shell particles studied recently in the literature.

Effects of gain medium on the plasmonic enhancement of Forster resonance energy transfer in the vicinity of a metallic particle or cavity.

We perform theoretical studies on the plasmonic enhancement for the Forster resonance energy transfer (FRET) between a donor and an acceptor molecule in the vicinity of a metallic particle or cavity, with focus on the possible role of the addition of a clad layer of gain material can play in such a process. The results show that while the plasmonic resonances can be shifted with higher order plasmonic enhancements emerged in the presence of such a layer of gain material, optimal enhancement of the FRET rate can be achieved when gain just balances with the loss in the metal. This then leads to the existence of an optimal thickness for the gain material layer, for both particle and cavity enhancement. In addition, it is observed that the FRET efficiency can always be increased with the coating of the gain material even at the dipole plasmonic resonance when nonradiative transfer from the donor to the metal is high, provided that the gain level is not beyond a certain critical value.

Two-dimensional near-field intensity distribution of tapered fiber probes

The near-field intensity distribution perpendicular to the light-propagation direction was measured by photochemical processes on conjugated-polymer thin films. The shape of the distribution is elliptical, with the long axis along the direction of the incident polarization. The results are compared with calculations based on the realistic tapered probe geometry. The asymmetry distribution is due to the simultaneous presence of horizontal and vertical electric fields in the near field.

Optical soliton in graded-index waveguides.

We show that optical solitons in a broad spectral range can be excited by propagating an off-axis Gaussian beam in nonlinear graded-index (GRIN) waveguides. Owing to periodical variation of both the beam size and dispersion coefficient in GRIN waveguides, the solitons belong to a newly discovered class called guiding-center solitons. In planar GRIN waveguides, solitons may be arranged to interact in both the temporal and spatial domains, thus the waveguide may serve as a novel platform for soliton interactions.

Reciprocity in nonlocal nano-optics

The principle of optical reciprocity is examined in the long wavelength limit in the presence of an isotropic nonlocal medium, by generalizing a previous result established in the literature on the symmetry of the Greens function. Our focus here is in its possible application to plasmonics, i.e.?optics with metallic nanostructures. It is shown that reciprocity will still hold as long as the dielectric function is symmetric with . Hence, under this symmetric condition, anisotropic dielectric response is necessary for the breakdown of reciprocity in the long wavelength limit. We further show in the appendix that this breakdown only occurs for an asymmetric dielectric tensor, in both the local and nonlocal response cases. An example is given to illustrate this symmetry in the problem of an emitting dipole interacting with a metallic nanoparticle whose response is described by certain dielectric functions which are both frequency and wavevector dependent.