We consider a nonlinear system formed by a thin nematic slab immersed in vacuum, submitted to the action of a high-intensity normally-incident plane electromagnetic wave. We solve simultaneously, by using a numerical scheme, the director's orientational configuration and Maxwell's equations for this system using homeotropic soft boundary conditions. For a given field intensity, we find multiple equilibrium director's configurations. In addition, we study the reflectance versus the wavelength and the field intensity.