Conference Agenda

We theoretically show that under circularly polarized plane wave or vortex beam illumination, the second-harmonic circular dichroism is possible even if the nanostructure is achiral. The interplay of nanostructure's and crystalline lattice's symmetries leads to specific conditions for observation of the circular dichroism, which can be expressed by a short formula. This can be particularly important for chiral sensing enhancement with nanostructure, where it is important to separate the signal from the nanostructure itself.

In recent years a strong drive towards the miniaturization of nonlinear optics has been motivated by the functionalities it could empower in integrated devices. Among these, the upconversion of near-infrared photons to the visible and their manipulation is fundamental to downsize optical information. We realized a dual-beam scheme whereby a pulse at the telecom frequency ω (λ=1550 nm) is mixed with its frequency-doubled replica at 2ω. When the two pulses are superimposed on a nonlinear, all-dielectric metasurface two coherent frequency-tripling pathways are excited: third-harmonic generation (THG, ω+ω+ω) and sum-frequency generation (SFG, ω+2ω). Their coherent superposition at 3ω produces interference, which we enable by filtering the k-space with the metasurface diffraction. The emission routing among diffraction orders is sensitive to the relative phase between the two pumps. Therefore, by exploiting the phase difference as a control mechanism, the upconverted signal can be commuted between diffraction orders, with measured visibility >90%. The proposed approach can be envisioned as an all-optical method to route upconverted telecom photons.

Lattice resonances (LR), collective electromagnetic modes supported by periodic arrays of metallic nanostructures, produce very strong and spectrally narrow optical responses. Usually, they arise from the coherent interaction between the localized electric dipolar plasmonic modes of the individual constituents of the array. Unfortunately, a two-dimensional arrangement of electric dipoles cannot absorb more than half the incident power due to fundamental symmetry reasons, thus hindering the use of LRs for applications requiring an efficient absorption of light. In this communication, we report a novel approach to overcome this constraint, which is based on the use of an array made of a unit cell containing one metallic and one dielectric nanostructure. Using a rigorous coupled dipole model, we show that this system can support two independent LRs, one with magnetic and the other with electric dipolar character, whose properties are tuned independently by adjusting the periodicity of the array and the size of the nanostructures. Furthermore, we show that an appropriate choice of these parameters not only leads to perfect absorption but also to quality factors exceeding 10^3. This work provides a general framework to design and implement complex 2D arrays capable of sustaining LRs with perfect absorption.

Photonic crystal slabs (or patterned multilayer waveguides) are known to support truly guided modes with no losses, as well as quasi-guided modes that lie in the continuum of far-field radiation. In this contribution, we present a guided-mode expansion approach – and the corresponding free software named “legume” – that allows calculating a number of features of quasi-guided modes of photonic crystal slabs: (a) symmetry properties and the issue of polarization mixing in coupling to far-field radiation modes; (b) the occurence of bound states in a continuum, which have infinite Q-factor and give rise to topological singularities of the far-field polarization; (c) the description of active two-dimensional layers through a suitably formulated light-matter coupling Hamiltonian, allowing to describe the regime of strong coupling leading to photonic crystal polaritons. Comparison with rigorous coupled-wave analysis, and the insurgence of non-hermitian features in the optical properties, are also addressed.

We report the fabrication and validation of an experimental system that exploits plasmonic Au nanoparticles to generate heat on a nanometric lateral scale, and measures the local temperature increase in the surroundings of these nanoparticles by means of carefully placed monolayers of transition metal dichalcogenide (TMDC).