Nonlinearities induced by magnetic fields in nematic liquid crystals

We investigated a nonlinear phenomenon arising when a planar oriented NLC cell introduced into a magnetic field was subjected to a laser beam with normal incidence. The limit number of diffraction rings was measured for different magnetic fields, higher than the critical one for the magnetic Freedericksz transition. A dynamical measurement of the fringes number was made for a magnetic field equal to the one for which the maximum number of rings was obtained. Another dynamical measurement was made for a higher field and, in all the cases, the theoretical approach was in good agreement with experimental data.