Effect of Convection on the Distortion of Spatial Self-Phase Modulation Pattern in Graphene Dispersions

Effect of convection on the distortion of spatial self-phase modulation(SSPM)pattern in graphene dispersions has been investigated. When a Gaussian laser beam is transmitted through grapheme dispersions, the interference pattern in the far-field first forms a series of circular rings, but the upper half of the rings collapses rapidly after a period of time, forming a stable distorted pattern. Experimental results show that thermal convection effect plays a dominant role for the distortion of the SSPM pattern. In the absence of convection in the beam cross section, the interference rings are circularly symmetric rings. In the presence of convection in the beam cross section, the interference rings exhibit circularly asymmetric rings. Theoretical analyses have then been given for the reason of the interference rings distortion. Convection can effectively change the spatial symmetry distribution of polarized graphene sheets and non-linear refractive index in the beam cross-section, thus making the interference rings distortion based on the spatial self phase modulation. It is concluded that the distortion of the interference pattern is originated from the thermal convections induced by laser heating. (paper)