Advances in 4/ phase coherent imaging technique for measuring the optical nonlinear index

4f phase coherent imaging technique is a simple and effective technique for measuring the third-order nonlinear index. Its principle, actuality and applications was introduced. An improved 4f phase coherent imaging system was proposed, which improved the reference optical path of traditional the 4f phase coherent imaging system to make the reference plot observing the pulse energy can be used to observe the space distribution of incidence pulse at the same time. By inputting the reference figure, the impact of the instability of the pulse can be avoided. Therefore, the improved 4f phase coherent imaging system can be used to measure the nonlinear index, when the pulses are unstable. The latest progress was also reported-a pump-probe system based on the nonlinear-imaging technique. This new system is helpful to simultaneously measure the dynamic nonlinear absorption and refraction conveniently.