Nonlinear optical and thermal properties of BCP: PMMA films determined by thermal self-diffraction

Abstract

Abstract The third-order nonlinear optical properties of Bromocresol purple (BCP): PMMA films are determined by means of thermal self-diffraction using continuous-wave (cw) diode laser beam with a wavelength of 473 nm and a laser power output of 40 mW. The magnitude of the nonlinear refractive index, n 2 , is determined based on the diffraction ring patterns obtained as a result of thermal self-diffraction induced by self-phase modulation. The results indicate that BCP: PMMA films have large nonlinear refractive index, n 2, for near resonance absorbance under 473 nm excitation. This happens since the energy of the excitation at 473 nm is nearer to the gap energy of the BCP: PMMA films, hence it is expected that the linear absorption and the nonlinear optical properties of this medium to be large at this wavelength. The nonlinear refractive index, n 2 , the change in refractive index, Δ n , and the thermo-optic coefficient, d n /dT, are in the order of 10 −5 cm 2 /W, (0.0088–0.039), 10 −5 K −1 respectively.