Symmetrical positive-negative annular phase object for optical nonlinearity characterization

A novel symmetrical positive-negative annular phase object (PNA-PO) is proposed in the 4f coherent imaging system and a third-order nonlinear refraction of the material is measured. By decomposing the normalized incident field passing through the PNA-PO into three top-hat beams with various radii and phase delays, and by using some applicable approximations, analytical solution of the phase contrast signal ΔT is revealed. Furthermore, variations of the analytical solution and numerical simulation of ΔT as a function of the on-axis nonlinear phase shift ϕ0 are shown. CS2 as a standard sample is performed using a PNA-PO to illustrate the feasibility and predominance of our system.