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

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, n2, 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, n2, 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, n2, the change in refractive index, Δn, and the thermo-optic coefficient, dn/dT, are in the order of 10−5 cm2/W, (0.0088-0.039), 10−5 K−1 respectively.