Optical, nonlinear optical, and electrooptical properties of 4´-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA) crystals

Optical, nonlinear optical, and electrooptical pg-properties of 4´-nitrobenzylidene-3-acetamino-4-methoxyaniline (MNBA) single crystals have been investigated. The refractive indices were determined in the wavelength range of 514 to 1064 nm using an interferometric method. The electrooptical coefficients r₁₁, r₁₃, r₃₁ , and r₃₃ were measured using a phase modulation technique. The dispersion of the largest electrooptical coefficient, r ₁₁ (=29 pm/V at λ=633 nm), was seen to follow the theoretical two-level model. Using the standard Maker fringe technique, we determined the nonlinear optical susceptibilities. The largest coefficient was found to be d₁₁=175 pm/V at λ=1064 nm. Electric-field-induced second-harmonic generation was used for the determination of the molecular second-order nonlinear optical susceptibility yielding a good quantitative agreement when compared with the largest nonlinear optical and electrooptical coefficients in the framework of the molecular gas model with charge transfer along the polar molecular axis. Electroabsorption measurements near the band edge were performed that allowed us to calculate the field-induced frequency shift of the dominant oscillator. This field-induced frequency shift is of the same order of magnitude as the frequency shift calculated from the electric field-induced changes of the refractive indices (electrooptical effect)