Dual beam thermal lens and z scan studies of the thermo-optical properties of some nonlinear materials

Abstract

We report a study on the thermo optical properties of some nonlinear materials using the z scan technique. Both open aperture and closed aperture z scan transmittance signals were recorded to study the refractive and absorptive nonlinearities. The samples chosen were metal phthalocyanines viz CoPc, NiPc, ZnPc and CuPc. Dimethyl Formamide (DMF) and Dimethyl Sulphoxide (DMSO) were used as solvents. The laser source was the Q switched Nd: YAG with 10 Hz repetition rate and a pulse width of 7 ns. The Q switched envelope of the pulses give negative nonlinearity in all these samples which can be due to either thermal lens effect or electronic transitions among triplet states. Usually the thermal lens effect is neglected in z scan signals recorded using high repetition rate pulses. In our work, we have also carried out dual beam thermal lens measurements inside the sample, using a low power He-Ne as probe. We used the theory of the thermal lens formalism and also that of the Kerr type nonlinearities to interpret the obtained data. These studies yield the nonlinear optical constants and also the thermo optic constants of the samples under investigation.