In situ intensity profile measurements of spatial quasi-solitons in thick dye-doped liquid crystal samples

We describe an experimental approach to measure the actual size of a narrow beam interacting non-linearly with a liquid crystal medium and experiencing a quasi-soliton-like propagation. We show that it is possible to accurately record the beam shape in two dimensions and at different stages of the self-focusing process by introducing within the sample itself a probe fibre as a detector and by scanning it across the beam profile. We discuss the influence of the probe fibre on the temperature distribution and the self-waveguiding process.