Sensitivity of the 4f coherent imaging system used in degenerate multiwave mixing experiments

We analyze the influence of different objects on the sensitivity of using a 4f imaging system for nonlinear optical measurements. By defining the diffraction efficiency as the physical quantity to measure, it is possible to perform different measuring methods (Z-scan, eclipsing Z-scan, I-scan, degenerate four-wave mixing) by matching the field stop in the image plane with the object at the entry. One, two, three, and four waves mixing are considered in order to compare their related sensitivities. We provide simple quadratic relations for each object that allow the characterization of the cubic optical nonlinearity. A systematic comparison is done showing that one circular aperture object gives the highest sensitivity. The experimental measurements are performed in order to validate our simulation. (C) 2009 Optical Society of America