Phase Scan Technique for Measuring Phase of Complex X~((3)) of Nonlinear Polymer Thin Films

摘要

A practical technique for absolute measurement of the complex phase of the third-order nonlinear optical susceptibility X~((3)) in thin films was developed using forward Degenerate Four Wave Mixing (DFWM) in the BOXCARS configuration. An apparent variation of the complex phase of X~((3)) with pump laser intensity was observed in highly nonlinear polymers. Detailed numerical models of the DFWM process were used to simulate the nonlinear interaction and it was found that this apparent intensity dependence can be explained by relatively efficient generation of phase mismatched beams. A procedure for calculating the correct phase of the nonlinear susceptibility from the data is presented and the effects of beam quality, both temporal and spatial, are discussed. It is shown that this technique does not depend on knowledge of the magnitude of X~((3)) and is absolute in the sense that it does not require a separate reference material, such as fused silica.