  Thanks to their unique properties, nematic liquid crystals feature a variety
of mechanisms for light-matter interactions. For continuous-wave optical
excitations, the two dominant contributions stem from reorientational and
thermal nonlinearities. We thoroughly analyze the competing roles of these two
nonlinear responses with reference to self-focusing/defocusing and, eventually,
the formation of nonlinear diffraction-free wavepackets, the so-called spatial
optical solitons. To this extent we refer to dye-doped nematic liquid crystals
in planar cells and continuous-wave beams at two distinct wavelengths in order
to adjust the relative weights of the two responses. The theoretical analysis
is complemented by numerical simulations in the highly nonlocal approximation
and compared to experimental results.
