Tailored nonlinear optical properties of nitro chalcones-doped PMMA thin films under femtosecond laser excitation

This study presents the comprehensive investigation of methyl- and bromothiophene-substituted nitro chalcone (ML3NC and 5B2SNC)-doped PMMA thin films fabricated via spray pyrolysis, focusing on their structural, linear, and third-order nonlinear optical properties. The TEM analysis shows tiny polycrystals embedded within the polymer matrix. Average thickness of the films by profilometer was measured to be 170–220[Formula: see text]nm. The linear absorption and transmittance spectra were studied in the UV–Vis–NIR region. The linear refractive index and the energy bandgap of the thin films are calculated to be 1.22–1.26 and 3.50–3.89[Formula: see text]eV, respectively. The PL emission wavelengths were observed in the visible range and the intensity increased with the doping percentage. Third-order NLO properties are studied using Z-scan under 150[Formula: see text]fs laser pulses at 800[Formula: see text]nm. The observation of three-photon-assisted reverse saturable absorption and negative nonlinear refraction demonstrates unique optical behavior. The films exhibit low optical limiting thresholds and satisfy key figures of merit for all-optical switching, indicating their strong potential for advanced photonic applications.