  We show theoretically that thermomechanical effects in dye-doped nematic
liquid crystals when illuminated by laser beams, can become important and lead
to molecular reorientation at intensities substantially lower than that needed
for optical Fr\'eedericksz transition. We propose a 1D model that assumes
homogenous intensity distribution in the plane of the layer and is capable to
describe such a thermally induced threshold lowering. We consider a particular
geometry, with a linearly polarized light incident perpendicularly on a layer
of homeotropically aligned dye-doped nematics.
