Structure of $\pi$- and 2$\pi$-walls in smectic films

The structure of $\pi$- and 2$\pi$-walls in smectic films was reconstructed from optical reflectivity measurements. Investigations were made in free standing films of nonpolar Smectic-$C$ and ferroelectric Smectic-$C^*$ liquid crystals. $\pi$-walls are observed in magnetic field and 2$\pi$-walls in electric field parallel to the film plane. For the first time the distribution of molecular orientation across the walls was determined. Peculiarities of the wall structure related to the anisotropy of the film elasticity were found. The structure of the walls is well described by the theory taking into account the anisotropy of two-dimensional elasticity of smectic films.