Anomalous behaviour of photoactive free-standing smectic films under illumination

Illumination of free-standing smectic films doped with azo dyes produces bubbles in the SmA phase; these cannot be observed in bulk samples. The bubbles appear in the films with some time delay after the beginning of illumination. This time delay depends linearly on (T-IA -T), where T-IA is the smectic A-isotropic transition temperature. This dependence shows that illumination induces in the interior of the films a smectic A-isotropic phase transition. The SmC* in-plane director field configuration depends on the orientation of the polarization plane of the incident light. In the SmC* phase no bubbles are observed even on continuous illumination.