Three-dimensional microscopy of laser-produced plasmas using third-harmonic generation

A three-dimensional microscopy of an optical-breakdown plasma based on third-harmonic generation (THG) is experimentally implemented. THG is shown to offer a universal method for three-dimensional microscopy of inhomogeneities of linear and nonlinear optical parameters of various media. Due to the nonlinear-optical character of this process, THG microscopy allows the transverse spatial resolution to be considerably improved as compared with conventional methods of microscopy. A high spatial resolution along the direction of probing is achieved due to the fact that the prohibition on THG in the regime of tight focusing is removed whenever inhomogeneities of linear and/or nonlinear optical parameters are probed by THG.