Polaritons. Surface Plasmon polaritons. New materials and applications. Laser-material interactions

Recently Surface Plasmon polaritons (SPPs) are attracting significant attention due to their potential in a variety of exciting applications (e.g. metamaterials with negative index of refraction, “cloaking", superlenses, etc.)

What are SPPs? When light strikes a conducting thin film it is possible to excite a surface plasmon polariton i.e. charge oscillations in the metal that lead to evanescent surface electromagnetic waves propagating along a metal/dielectric interface. The surface plasmon resonance is highly confined at the interface and therefore it is very sensitive to the dielectric optical properties.

For the surface plasmon resonance to be excited, the incident light wave vector must match the surface plasmon resonance momentum. This is possible when:

How can the surface plasmon be excited? Using polarized light and adequate coupling: (i) Kretschmann configuration; (ii) diffraction gratings; etc.

Highly correlated oxides and metal/insulator studies. We have received and NSF award targeting fundamental understanding of the insulator-to-metal phase transition in VO₂ (and similar transition oxides) thin films, which still remains a challenge for both theory and experimental physics. This is a team effort with Professor Irina Novikova. Our most recent results can be found here. We will use various aspects of surface Plasmon excitation in this project. Our immediate plans also include carrying out time-resolved studies using ultra-fast laser pulses. We have acquired a new laser amplifier to complement existing facilities in our Center for Ultra-fast laser studies. Laser fest activities funded by a proposal from APS-OSA have been developed as part of the broader impact of this project.

New Photocathode materials for Electron-ion-colliders. We have recently received a DOE grant toward the exploration of plasmonic photocathodes, essential to develop strategies and technologies for next generation nuclear physics accelerator capabilities, particularly for Electron Ion Colliders (EIC). There is an urgent need to develop alternative materials capable of handling high currents for long periods of time. This suggests the use of more robust metallic cathodes, inherently sturdier. Since metallic photocathodes also exhibit very low QE due to poor light absorption, plasmonic excitation via nano-patterning can be used to enhance light absorption, hence also QE.

Magneto-plasmonic materials for biological and environmental applications

One of our recent research projects funded by DARPA, involved the development of novel magneto-optical sensors to be used in biological sensing applications based upon plasmon enhancement of the magneto-optical response. Magnetic materials embedded in plasmonic matrices, are expected to exhibit novel magneto-optical properties whose phenomenology has not been addressed so far. In particular we can use the magnetic field dependent part of the optical response in these nano-composite thin films to modulate the optical surface and thus enhance its sensitivity. We studied Au-Co-Au trilayers and magnetic Co nano-clusters embedded on noble metal surfaces (Ag, Au) to exploit the enhancement of the surface plasmon resonance of the nano-composite film in reflection geometry. To achieve these interesting optical properties we are investigating several nano-fabrication approaches to tailor the structure of these nano-composite materials. We are also investigating the use of diffraction gratings to couple photons and plasmons. In addition we have investigated the enhanced magneto-optical activity of core-shell nanoparticles when localized surface plasmons are excited.

Recent results on magneto-optical enhancement of SPR can be found here.