Linear and nonlinear optical properties in Langmuir–Blodgett multilayers of new cyanine dye

We investigated on cyanine dye (HQ) in Langmuir and Langmuir–Blodgett (LB) films by UV–vis spectra and second-harmonic generation (SHG) methods. UV–vis spectra indicated a uniform film transfer. The significant SHG fringe signal as a function of angle of incidence for Z-type LB films was observed respectively. The refractive indexes at 532 nm and average tilt angle ψ between the molecular (dipolar) axis and surface normal from fitted SHG data are 1.4841, 57° and 1.4775, 53° without and with Cd²⁺ ions, respectively. The second-order susceptibility and 32 pm V⁻¹ for LB films with and without Cd²⁺ ions are obtained by measuring SHG signals. These high nonlinearities are due to resonant enhancement resulting from the proximity of the second-harmonic wavelength to the absorption band of the films.