Nonlinear polarimetry of molecular crystals down to the nanoscale

Molecular nonlinear optics is currently experiencing a fruitful revival as a result of the unprecedented possibility to experimentally access the nanoscale through adequate nanophotonics instrumentation and modelling. It is the purpose of this article to survey and discuss some ongoing developments in this domain within our laboratory, with special emphasis on polarization dependent tensorial properties read-out at submicron scale, to be exploited towards a better understanding of nanostructured architectures, ordering as well as dynamical crystallization properties of a variety of samples, down to the spatial resolution of two-photon nonlinear confocal microscopy. The advantages of combining coherent (e.g. second harmonic generation) and incoherent (e.g. two photon induced fluorescence) phenomena, moreover with polarization resolution, will be shown to open-up a new and unique pathway onto the orientation as well as crystalline quality of different types of nanocrystals (from one component molecular to mixed guest-host binary crystals). The oriented gas model, expressed in its most general invariant form by way of irreducible multipolar decomposition permits to identify generic types of nonlinear polarization patterns which potentially provide both qualitative and quantitative insight onto the structural properties of a broad variety of molecular as well as inorganic nanomaterials.