Finger forming optically induced phase transition in dye-doped liquid crystal

Interfaces between two phases may exhibit enthralling shapes. Optically driven phase transitions are a benchmark that enables spatial control in the order parameter. Dye-doped liquid crystals allow purely optically induced phase transitions. Here we show the temporal evolution of finger-like structures at the nematic-isotropic interface in a photoisomerization experiment in a liquid crystal mixture between E7 and methyl-red dye in twisted planar cells both in the turn-on and turn-o of light scenarios. From the nematic to isotropic liquid transition, triggered by turning on the light, the emergence, growth, and retraction of finger-like structures are observed and characterized. In contrast, the isotropic-to-nematic phase transition when the light turns off transient foam-like and labyrinthine textures are observed. A reduced model based on dopant concentration and the liquid crystal order parameter reproduces all the observed phenomena.