Emerging Leaders Program

Ellen Williams Distinguished Postdoctoral Fellowship
Research Topic: Time-Domain Nanoscience

Nanowire Plasmonics

Advisor(s):

Prof. Sang Bok Lee and Prof. John Fourkas

Research Description

Metal nanostructures have unique optical properties that are of great potential importance in photonic applications. One of the great advantages of metals in photonic applications is that the refractive index of the medium is high enough that light (in the form of propagating plasmon-polariton modes) has a wavelength that is much shorter than in vacuum. As a result, metallic waveguides can be considerably smaller than their dielectric counterparts, opening the door to important new applications in areas ranging from photonic circuitry to nanophotolithography.

The bulk of the research in nanoscale plasmonics to date has involved static properties and/or continuous-wave light. As a result, few studies have taken advantage of another key aspect of metal nanostructures: optical nonlinearity. Nonlinearity can be accessed readily via the use of ultrafast lasers, which have high peak intensity but low average power. We are proposing to use ultrafast lasers to study and harness optical nonlinearity in metal nanowires. Nonlinear effects such as multiphoton absorption and harmonic generation will allow us to generate and propagate light at wavelengths that are far different from that used for excitation. The delivery of short-wavelength visible or near-UV radiation in a nanoscale region will have many important applications in nanophotonics and optical technology. The ability to deliver guided light of different wavelengths via nonlinear interactions will be an enabling technology for many applications in nanophotonics, including nanophotolithography, nanoimaging, and photonic circuitry.

Progress Upate:

Researcher - Dr. Samrat Dutta, Sang Bok Lee and John Fourkas Groups
Resume

We report the coupling of free space photons with plasmonic waveguides propagating towards a metallic tip. This provides the ability to confine optical energies in small volumes which can cause large field enhancements. Such field enhancements can offer benefits in biosensing, nanolithography, data storage and can act as a nanofocusing device. By using electodeposition and electrodisolution techniques, we have prepared and characterized tapered metallic silver nanowires and their interaction with far-field excitation.

The prepared nanowires are long cylindrical wires with one end adiabatically tapered to achieve a nanofocusing effect. Focused light illuminated at the ends of such tapered nanowire can launch propagating plasmons along the length of the nanowire. We observe that the launch of the propagating plasmons and their far-field emission is selective and occur only at ends. In addition, the far-field radiation couples very efficiently from the flat end to the tapered end, with minimum luminescence at the excited end. However, we fail to couple free space photons with the propagating plasmon modes when we focus the laser directly onto the tapered end. Our characterization of the luminescence behavior in the far-field clearly shows the polarized nature of the luminescence. This confirms the established notion that plasmon can be only be excited along the long axis of the wires at our excitation wavelength. In our far-field imaging technique, we can clearly segregate the guided luminescence and their polarized nature.