Nichtlineare Wechselwirkungen in einkristallinen plasmonischen Nanoschaltkreisen

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In the upcoming funding period of the project we plan to investigate the influence of nonlinear optical effects on the propagation of ultrashort plasmon pulses. Nonlinearities are essential for the implementation of plasmonic circuitry since they will allow the manipulation of plasmons by plasmons. Due to the strong field localization and enhancement, nonlinear effects can be significantly enhanced. However, the nonlinear propagation of plasmon pulses has rarely been investigated experimentally. Our experimental setup provides a unique opportunity to study the amplitude and phase modification of propagating plasmons due to nonlinear interactions. Nonlinearities that will be investigated are the ponderomotive nonlinearity of plasmonic materials themselves, the free-carrier nonlinearity of e.g. ITO-substrates, as well as Kerr-type nonlinearities of the substrates or well-positioned nanoparticles, such as Chalcogenide glasses. Depending on the type of nonlinearity, we will design plasmonic elements that support well-chosen mode patterns to achieve maximal effects. We will also employ well-designed excitation geometries for specific modes. For the implementation of advanced nanostructures, beyond the commonly used single straight wires, we will build on focused-ion beam patterning of single-crystalline gold as developed during the first phase of the project. We will also evaluate the use of He-ion milling to fabricate structures with extremely fine details. The final goal of the project is the implementation of functional plasmonic elements such as switches and couplers that take advantage of the richness of nonlinear interactions as opposed to basic linear interferometric control. Experimental studies will be performed on two exemplary circuits: (i) a two-wire transmission line featuring a local bottleneck in which strong mode localization occurs and (ii) a straight two-wire transmission line with a high-local-intensity resonant stub that suppresses transmission under action of a Kerr-like nonlinearity. Nonlinear effects will be characterized by (a) the appearance of new modes which are detected via different angular-spatial emission patterns, (b) measuring changes of transmission and group velocities, and (c) analyzing the time-domain structure of the emitted signal as a function of the pulse’s peak intensity.