Spatial self-phase modulation in liquids and solids

Here we review the spatial self-phase modulation in nonlinear refraction, with a brief introduction of the origin and development of nonlinear optics. With a powerful laser irradiating a nonlinear medium, we can observe bright and dark fringes, namely interference rings, in the far field. In this paper we analyzed the formation mechanisms of interference rings from liquid (water as an example), liquid crystal and low dimensional material suspension. For most liquids, the main reason for the formation of the interference rings is the optical path difference caused by the temperature distribution in the liquid. Because the laser light intensity has a Gaussian distribution, the liquid at different positions is heated differently, so the refractive index of local liquid is no longer the same, resulting in optical path difference (thermal lens effect). The interference rings contain abundant information about the physical properties of materials, while the thermal effect also affects the performance of optical instruments. A thorough understanding of spatial selfphase modulation will help us use or eliminate the thermal lens effect.