  An optically-induced thermal non-linear effect in a nematic liquid-crystal
(E7) cell is evidenced through weak light-absorption by the ITO coating of an
infrared pulsed femtosecond laser (m). Strong spatial self-phase modulation is
generated, thus a multiple-ring pattern is observed in the far-field. The sign
of the nonlinearity is changed depending on the laser polarization. The
refractive index and thermal gradients are measured as a function of the laser
intensity and we observe that the temperature can increase close to the nematic
phase transition. The fidelity and stability of the process open new prospects
for spatial shaping devices and delimits the operating wavelength range for
ultrafast liquid-crystal based electro-optic application.
