Study of thermal lens technique and third-order nonlinear susceptibility of PMMA base containing 5′, 5′′-dibromo-o-cresolsulfophthalein

Measurements of the third-order nonlinear susceptibility of 5′, 5′′-dibromo-o-cresolsulfophthalein (BCP) in a chloroform solvent were studied using a cw diode laser at 532 nm as the source of excitation, both in solution and as a poly methyl methacrylate solid film, respectively. The optical response was characterized by measuring the intensity-dependent refractive index (n ₂) of the medium using the Z-scan technique. The sample showed negative and large nonlinear refractive index values of the order of 10⁻⁷ cm²/W and reverse saturable absorption with high values of the nonlinear absorption coefficient of the order of 10⁻⁴ cm/W. The nonlinear refractive index was found to vary with the concentration. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. Thermal lens technique was applied to investigate the thermo-optical properties (dn/dT) and the thermal diffusivity (D). In this technique a pump beam was aligned collinearly. A localized change in the refractive index of the sample due to the thermal heating produced a thermal lens that was then detected by the study of the focusing and defocusing of the pump beam. Morphological of a one-dimensional microscopic image surface profile scan and histogram curve of the film surface has been studied.