Light intensity modulation in hybrid plasmonic crystals using propagating modes

Abstract

This thesis explores the influence of sample magnetization and coherent lattice vibrations on the reflection and transmission properties of periodically nanostructured metal-dielectric structures known as hybrid plasmonic crystals. The optical excitation of surface plasmon polaritons, bound modes of the electro-magnetic field at the metal-dielectric interface, leads to an increased sensitivity to changes of the dielectric environment in such structures. The first part of this thesis deals with the plasmonic enhancement of magneto-optical intensity effects causing a difference in the reflected and transmitted light intensity in dependence of an applied magnetic field. First, two different plasmonic crystal designs based on magneto-optical dielectrics are investigated with respect to their ability to modulate the transmitted light intensity by application of a transverse magnetic field. A significant enhancement of the achievable intensity modulation compared to samples based on ferromagnetic metals is found. Furthermore, a novel effect arising for the longitudinal magnetization geometry in such periodic structures is described theoretically and verified experimentally. The magnetization induced mixing between different types of waveguiding modes in the investigated magneto-plasmonic crystals is identified as the driving mechanism behind the observed intensity modulation in transmission and reflection. In the second part of the thesis optical pulses are used as an external stimulus to alter the reflection behavior of plasmonic crystals. First, the influence of nanosecond pulses on the magnetization in a nickel-based plasmonic crystal is investigated through the induced spectral shift of a surface plasmon polariton resonance. Secondly, hybrid semiconductor-plasmonic crystals based on II-VI semiconductors are studied by means of femtosecond pump probe spectroscopy. A modulation of the reflected light intensity at terahertz frequencies is observed for these structures. The origin of the transient signals can be traced back to a plasmonically assisted segregation of elemental tellurium followed by the excitation of coherent crystal lattice vibrations influencing the surface plasmon polariton resonances sustained by the investigated samples.