Banca de QUALIFICAÇÃO: NEFE JEFFERSON DE BRITO E SILVA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE: NEFE JEFFERSON DE BRITO E SILVA
DATA: 10/02/2026
HORA: 14:00
LOCAL: Auditório do Departamento de Física
TÍTULO: Efeito Termo-Óptico na Norbixina: Caracterização por Varredura-Z e Automodulação de Fase sob laser CW
PALAVRAS-CHAVES: Natural Dyes; Nonlinear Optics; Norbixin; Spatial Self-Phase Modulation (SSPM); Thermal Lens Effect; Z-scan
PÁGINAS: 40
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

This work investigates the thermal nonlinear optical properties of norbixin, a natural dye extracted fromBixa orellana L. seeds, dissolved in acetone. The molecular structure and optical response were characterized using UV-Vis, FT-IR, and Raman spectroscopies. The optical band gap was estimated to be2.40 eV using the Tauc plot method, indicating that the excitation at 532 nm (hν = 2.33 eV) occurs in anear-resonant regime. Nonlinear optical properties were investigated using the Z-scan technique and the
analysis of far-field diffraction ring patterns under continuous-wave (CW) laser illumination. Open-aperture Z-scan measurements revealed saturable absorption (SA) behavior, characterized by a negative nonlinear absorption coefficient of while closed-aperture Z-scan showed aclear peak–valley trace indicative of a strong self-defocusing effect, from which a negative nonlinearrefractive index on the order of was determined. A discrepancy of
approximately three orders of magnitude was observed between the nonlinear parameters obtained fromZ-scan and spatial self-phase modulation (SSPM). This difference is discussed in terms of concentration-dependent thermal loading, the presence of large on-axis phase shifts. The transition from a radially symmetric to a vertically compressed diffraction pattern confirms the influence of a convection-dominated regime under high-intensity CW. These results establish norbixin as a promising sustainable nonlinear optical material for photonic applications, including optical limiters and all-optical switches,while providing fundamental insights into thermo-optic effects and convection in nonlinear media.

MEMBROS DA BANCA:
Interno - 1570906 - BARTOLOMEU CRUZ VIANA NETO
Presidente - 1780191 - FRANCISCO ERONI PAZ DOS SANTOS
Externo ao Programa - 2092477 - HANS ANDERSON GARCIA MEJIA
Interno - 3374421 - LUCAS SOARES MARINHO