Nichtlinieare plasmonische Nanoantennen aus Lithiumniobat

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The successful exploration of nonlinear processes in nanostructured waveguides comprising lithium niobate in the first funding period led to a series of groundbreaking contributions. Examples are suggestions for novel phase matching schemes, clarifications on the ability to enhance the propagation length of surface plasmon polaritons guided in metallic waveguides by parametric amplification, but also adjacent topics were explored such as the first observation of an Airy-plasmon and the in-depth analysis of linear properties of optical nanoantennas. The challenging work that has been performed in a combined experimental and theoretical effort served the purpose to understand and to control the ultrafast nonlinear dynamics of light in optical nanostructures. In the second funding period, the methodology and the means previously developed will be used to study in a coherent continuation the ultrafast nonlinear dynamics of cavities made from finite metallic nanowaveguides embedded into a nonlinear surrounding made of nanostructured lithium niobate. The cavities essentially constitute optical nanoantennas where a guided mode bounces back and forth and eventually experiencing a resonant interaction where the plasmons suffering from multiple reflections constructively interfere. The raison d'être of these resonances are dictated by the phase accumulation of the plasmons propagating across the nanoantenna and a contribution from the phase of the complex reflection coefficient at the antenna termination. Both properties can be adjusted at will for the various frequencies involved in the nonlinear process by tailoring the geometrical cross section of the nanoantennas and the nanoantenna termination. This combination provides novel degrees of freedoms to achieve efficient nonlinear conversion inaccessible thus far. Moreover, the ability to tailor the radiation pattern of the optical nanoantennas will provide in perspective an integrated nonlinear light-source with directed emission and allows engineering parametric nonlinear processes well beyond the current state of the art by superimposing simultaneously various incidence fields. Based on the fundamental theoretical understanding and the developed experimental techniques we will target major challenges of the field, as e.g. Q-factor enhancement of plasmonic resonances by nonlinear parametric gain, generation of entangled photons in nanoantennas by spontaneous downconversion, or nanosized SHG light sources for high contrast sensor applications. The work we propose is an extension of our manifold activities in the previous funding period and fuses the leitmotifs and the main research direction of the priority program, i.e. nonlinearity, optical nanoantennas, propagation, and coherent control.