Study On Propagation Properties Of Light Beams In Negative-index Material Slab Lens

Negative-index material(NIM) is a kind of artificial synthetic material which has negative permeability and negative permittivity simultaneously, generally, its unique physical properties can not occur in ordinary material. In recently years, the NIM has been investigated from microwave range to optical range even extended into the field of beam propagation, it leads to a lot of new phenomena and characteristics, it has practical value for development of optical control technique and opto-electronic devices. In this paper, focal shift of paraxial Gaussian beams, focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams in NIM slab are investigated by combining the basic traditional theory of laser optics and the novel properties of NIM. The main obtained results are listed below:Firstly, based on angular spectrum representation, modles of beam propagation and paraxial Gaussian beams in NIM slab lens are presented, them are the basis of investigation about focal shift of paraxial Gaussian beams in NIM slab lens and the focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams in the NIM slab.Secondly, focal shift of paraxial Gaussian beams in NIM slab lens are investigated. According to the basic traditional theory of laser optics and the novel properties of negative-index material, the theory model for paraxial Gaussian beams in the NIM is obtained from the Maxwell equations. Based on Snell's law and characteristics of the beam boundary, we found there is no focal shift when a paraxial Gaussian beam passes through the NIM slab lens in the absence of absorption or gain, however, the effect exhibits in the presence of the absorption or gain, and becomes larger as the absorption or gain increase. When the absorption is equals to the gain, the phenomenon of the focal shift caused by the gain is more obvious. In addition, the field distribution is not affected by the absorption or gain and always keeps Gaussian both in internal and in external focus planes in the process of the beam propagation.Thirdly, based on angular spectrum representation, formalisms describing paraxial Hermite-Gaussian and Laguerre-Gaussian beams propagating through an isotropic NIM slab are presented, and the focusing and phase compensation of paraxial Hermite-Gaussian and Laguerre-Gaussian beams in the NIM slab are investigated from the equations. We introduce concepts of the inverse Gouy phase shift and the negative Rayleith length of paraxial beams because of the ngative index. The results show that the phase difference of beams which caused by Gouy phase shift in air can be compensated by the inverse Gouy phase shift in the NIM, so the phase difference between the object plane and the image equal to zero in the certain matching conditions. If conditions of focusing and phase compensation are satisfied simultaneously, intensity and phase distribution at object plane can be reconstructed at the image plane. The NIM slab is better than the traditional surface lens in the respects of beam focusing and phase compensation, it provides new technique for the beam propagation and control.