Strong self-focusing in nematic liquid crystals.

We present an experimental study of strong self-focusing in nematic liquid crystals. In a planar geometry, a linear dependence of the focal power on the input intensity for 100-μm-thick samples turns into an exponential one when thicker samples are used. A transverse visualization of the beam structure is performed in a cylindrical geometry. We observe an undulation and a filamentary structure of the laser beam for large intensities. Also, multiple focal points appear along the beam axis in this configuration. Undulation and filamentation of the beam are also observed in a spherical geometry