Nonlinear optical spectroscopy in two-dimensional materials and van der Waals vertical heterostructures

Abstract

Atomically thin nanomaterials have high second and third order optical susceptibilities. Such optical properties are mainly due to the low dimensionality, which promotes high binding energies and makes possible the existence of excitonic states at room temperatures. In this way, nonlinear optical spectroscopic techniques are important to the investigation of electronic and excitonic properties of these materials, while the control of the excitonic and energy levels of the material, either through the variation of the dielectric environment or the variation in the number of layers, has fundamental influence in its optical response. In this project we propose to investigation the electronic and excitonic properties of two-dimensional nanomaterials and their heterostructures via multiphoton microscopy in, substantially, three types of materials: a) franckeite, a naturally occurring two-dimensional material which potential for third harmonic generation has already been preliminarily demonstrated; b) hexagonal boron nitride, which excitonic properties have been studied recently and demonstrate great potential for harmonics generation below 400 nm; c) van der Waals vertical heterostructures, formed by monolayers of transition metal dichalcogenides, structures in which the presence of interlayer excitons can be controlled and explored for resonant harmonics generation in the visible and near infrared ranges. Our objectives are to better understand the excitons dynamics and its influence on the optical properties of two-dimensional nanomaterials; to determine which materials are most suitable for certain applications in order to improve optical conversion and wave mixing efficiencies in photonic and optoelectronic devices; and to establish how to modify nonlinear optical properties through stacking of these materials forming complex vertical heterostructures. (AU)