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First hyperpolarizability scattering in chiral organic polymers

Grant number: 17/12867-0
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): November 01, 2017
Effective date (End): June 30, 2018
Field of knowledge:Physical Sciences and Mathematics - Physics - Condensed Matter Physics
Principal Investigator:Leonardo de Boni
Grantee:Raian Gonçalves Westin
Home Institution: Instituto de Física de São Carlos (IFSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

This project aims at the use of a picosecond laser to obtain the HyperRayleigh scattering dependent on the polarization of light. This research method can be applied in both organic and inorganic materials, including biological materials. As one knows, one of the techniques most used to characterize chiral molecules is the circular dichroism technique, which can both obtain the difference in absorption as well as the rotational dispersion of light due to the interaction of the optical field with the chiral structure of the molecule. This technique works with linear effects of absorption and light refraction and is limited to obtain information only from the linear polarization of the material induced by the electric field. Another way of further quantifying the effects of light interaction with such materials is through non-linear optics. In this field of research, the linear polarization induced by the electric field is no longer the main focus of study, and other terms in the induced polarization (non-linear) are studied, which bring new information that can be related to the structure of the materials which are not obtained with conventional techniques of linear optics. The interaction of light with molecular structure can bring important information for the understanding of secondary structures of chiral molecules (DNA, amino acids and etc). In the present project, the main objective is to modernize the HiRayleigh technique in terms of its sensitivity with respect to the optical signal to be measured. In addition, it is intended to adapt the technique so that it is possible to control the polarization states of the optical fields (linearly polarized, circularly polarized left and right). After the implementation of this technique, it will be used to characterize and quantify the nonlinear effects in known organic materials, which may be dependent on light polarization. In a second stage of the project, it is intended to use such techniques to observe effects of non-linear dichroism on chiral molecules. It is known that the second order optical signal is very dependent on the structure of the material, the more asymmetrical the charge distribution, the greater the signal of it tends to be. Some new questions can be asked: How would the nonlinear scattering of light behave because of molecular chirality? It is possible to observe a signal difference between different polarizations of the optical field and what would be the importance of these results in the preparation of metamaterials. (AU)