On the inverse phase characteristics of Gaussian beams in negative refractive index materials

The phase characteristics of Gaussian beams in negative refractive index (NRI) slabs have been quantitatively investigated via the finite-difference time-domain (FDTD) method. The phase and magnitude distributions for both the normal and oblique incidences of continuous wave Gaussian beams are presented. For the normal incidence, all three contributions of the phase, i.e., plane-wave phase, radial phase and Guoy phase shift, have been shown to be the reverse of their counterparts in free space, which evidently reveals how phase compensation is caused by a NRI slab. Moreover, it is worth noting that our FDTD results are more accurate than the paraxial results in the case of a Gaussian beam propagating beyond the paraxial approximation.