中文摘要：

4f相位相干成像技术是测量三阶光学非线性的新方法。其原理是利用一个相位光阑将放置在4f系统频谱面上的非线性样品中产生的非线性相移调制成像平面上的振幅变化，从而测量样品的非线性折射率的大小和符号。常用的带圆形相位物体的相位光阑灵敏度随相位物体尺寸减小而增加，但是在相位物体很小的情况下制作难度很大，通常达不到最佳的灵敏度。通过将相位光阑中原来处于光阑中心的圆形相位物体改为半圆形相位物体，使得系统可以处于最佳灵敏度，相位光阑在制作工艺上的难度大大降低。

英文摘要：

The 4f coherent imaging system with phase object is a new memoa to measure me tirdorder optical nonlinearity. The sample to be measured was placed at the Fourier plane of the 4f system and a diaphragm with phase object was used to modulate the nonlinear phase shift to the amplitude change of the electric field in the image plane. According to the variation of the intensity in the nonlinear image, the sign and magnitude of the nonlinearity could be obtained. The system sensitivity with a diaphragm of circular phase object increased with the decrease of the size of the phase object. But it was difficult to manufacture such a small phase object, so the system usually didn＇t work at the best sensitivity. In our experiment, the circular phase object was changed into a semicircular phase object at the center of the diaphragm , the system can works at the best sensitivity while the semicircular phase object can be manufactured more easily.