Ricerc@Sapienza

This proposal aims at demonstrating experimentally the implementation of a super-continuum source based on enhanced nonlinearity in near-transition ferroelectric supercrystals for chromatic aberration-free pump-and-probe ultrafast spectroscopy.
Objectives of the project are:
O1. Design and demonstration of a pump-and-probe scheme based on a super-continuum source obtained by a nanodisordered perovskite.
O2. Demonstration of chromatic aberration-free spectroscopy based on giant broadband optical refraction.
The expected outcome is a method to overcome one of the principal challenges in state-of-the-art ultrafast spectroscopy: dispersion, chirp, and chromatic aberration in super-continuum pump-and-probe schemes. Such effects generate undesired nonlinear artifacts, hampering the detection and the interpretation of ultrafast time-resolved spectra, which require the use of pulses with an ultra-broad spectral bandwidth to ensure a femtosecond time resolution.
To achieve this goal, the proposal pools together the Ultrafast Spectroscopy Group (USG) and the Nonlinear Photonics Group (NPG) at the Physics Department, both active in the experimental study and development of innovative optics and materials.
The underlying idea is based on giant broadband refraction in the visible (n>25), a phenomenon observed when light propagates along the strings of 3D topological defects (spontaneous polarization vortices) that form as a nanodisordered ferroelectric KTN (potassium-tantalate-niobate, KTa(1-x)Nb(x)O3) is cooled through its room-temperature Curie point. Giant refraction causes an enhanced optical nonlinearity that allows constraint-free wavelength conversion and supercontinuum generation through nonlinear Cherenkov radiation, without chromatic dispersion and walk-off. The project will design and demonstrate ultrafast pulsed-laser experiments that use this enhanced optical nonlinearity as an aberration-free super-continuum source in cutting-edge spectroscopy.