Laser-induced diffraction effect from polypyrrylarylenemethine solution

A new type of π-conjugated polymer-Polypyrrylarylenemethine is designed and synthesized, which shows large nonlinear optical characteristics. It is discovered in experiment that as the 526 nm TEM₀₀ laser beam passing through the Polypyrrylarylenemethine/N-Methyl-2-pyrrolidone (NMP) solution, numbers of concentric diffraction rings arise in far field. This phenomenon can be explained by the spatial self-phase modulation of the Gaussian beam passing through the nonlinear medium. With theoretical analysis and numerical calculation, it is found that the transverse nonlinear phase shift caused by the sample can be very well fitted by a Guassian function. The nonlinear refractive index n₂ can be estimated according to the number of the diffraction rings. The n₂ of Polypyrrylarylenemethine/NMP solution is about-1.85×10^-3 esu.