Dynamical non linear diffraction pattern induced by photothermal effects in a liquid crystal film

In this work it is experimentally demonstrated that the nonlinear diffraction pattern produced by a dye doped nematic film exhibits a sequence of dynamical regimes. They are clearly distinguishable in the far field under the simultaneous action of a linearly polarized laser beam and a low frequency AC electric field. The values of the relevant control parameters like the power threshold or laser power were determined. The average angular velocity and the rotation period of the pattern were measured for the first observed rotationally stable regime. We briefly discuss a preliminary nonlinear model which proposes that the light absorption by the dye doped sample produces a temperature gradient that couples to the effects induced by the laser through an induced order polarization. This mechanism generates an additional torque which gives rise to some of the features of the observed rotational pattern

Measurement of low optical absorption in highly scattering media using the thermal lens effect

In this work we show that the thermal lens effect can be applied to highly scattering and weakly absorbing materials. We apply the thermal lens effect and the z-scan technique to estimate the effective absorption coefficient of a suspension of TiO$_2$ particles with a mean diameter of 220 nm at two wavelengths: 488 nm and 514 nm. From the effective absorption coefficient we estimate the absorption cross section of the particles