Banca de DEFESA: MAXWELL ARAGAO MARQUES NOGUEIRA
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.STUDENT : MAXWELL ARAGAO MARQUES NOGUEIRA
DATE: 15/09/2023
TIME: 10:00
LOCAL: Auditório do Departamento de Física
TITLE:
NONLINEAR OPTICAL SPECTROSCOPY OF MESOIONIC COMPOUNDS
KEY WORDS:
Mesoionic compounds. Optical nonlinearities. Hyperpolarizability. Two-photon absorption. Multi-photon absorption.
PAGES: 118
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:
Recent developments in nonlinear optical materials generally search for systems with improved second and third order optical properties, aiming at their use in optoelectronic devices, all-optical limiters, among other applications. In this context, important works focused on the exploration of new organic molecules have been published, focusing mainly on molecules with large nonlinear optical coefficients, fast response times, direct synthesis and processability. In particular, molecules with push-pull electronic structure, which give rise to the delocalization of π-electrons, present high optical hyperpolarizabilities and fast response to non-resonant excitation. Mesoionic compounds (MICs) belong to a class of materials that have great potential for nonlinear optics, as proposed more than two decades ago. Typical MICs have planar heterocyclic dipole structures in which the positive and negative charges are separated and delocalized within a π-electron system, resulting in permanent electric dipole moments that can reach 5D. In this work, we synthesize, characterize, and measure the second- and third-order nonlinearities of MICs from the 1,3-thiazolium-5-thiolate group, dissolved in dimethyl sulfoxide (DMSO) at room temperature. In measuring the second-order polarizability (first hyperpolarizability), we used the hyper-Rayleigh scattering (HRS) technique, operating at in the nanoseconds regime. The measured hyperpolarizability, was used to calculate the static hyperpolarizability, by applying the classical two-level model. By the measures of the first hyperpolarizability and the calculation of the fundamental limits we discuss the second-order optical performance of mesoionic molecules. The second-order nonlinearity of these molecules turned out to be relatively high compared to molecules of similar size. In third-order refraction and absorption measurements, we used the Z-scan technique in the picosecond (at 532 nm) and the femtosecond (at 800 nm) regimes. Under excitation at 532 nm, we observed a refractive behavior with self-defocusing, in the presence of nonlinear dissipative effects: two-photon absorption (2PA) and excited state absorption (ESA). Analysis of the results by the Fast Fourier BPM method, based on a three energy level model, revealed that the ESA cross section is one of the largest ever reported in the literature, being approximately 10 times larger than the linear absorption cross section starting from the ground state . Also noteworthy is the large value of the two-photon absorption cross section (3,7 x 104 GM), consistent with previous results. Normalizing this 2PA cross section, we quantified and discussed the molecular nonlinear optical performance, which indicated a great potential for applications in all-optical limiting and all-optical switching. On the other hand, applying the Z-scan technique, operating at 800 nm, the dependence of the non-linearity with the wavelength is evidenced from the three-photon absorption excitation (3PA).
COMMITTEE MEMBERS:
Interno - 1130294 - CELSO PINTO DE MELO
Presidente - 1129726 - CID BARTOLOMEU DE ARAUJO
Externo ao Programa - 1133583 - LUCIO HORA ACIOLI - nullExterno à Instituição - PETRONIO FILGUEIRAS DE ATHAYDE FILHO - UFPB
Interno - 1134371 - RICARDO LUIZ LONGO