非线性成像系统中样品损伤引起的伪非线性现象

4f相位相干成像系统是最近发展起来的一种利用单脉冲测量材料三阶非线性的技术.当使用这种技术对薄膜材料进行测量时,部分材料经过高光强照射以后会产生伪非线性图像.这里所说的伪非线性图像是指无论在强的或弱的激光光强照射下,被测量样品的实验结果中总是显示出与非线性材料在高光强下显现出的非线性图像相类似的实验图像.基于多种不同材料的薄膜样品的实验结果,对伪非线性图像的形成原因进行了研究.大量实验表明:伪非线性图像是由样品的两种损伤造成的:一种是样品被碳化或破坏(形成一个黑斑),另一种是样品被剥离或漂白(形成一个白斑).从实验和数值仿真两方面对观点进行了验证.

Pseudo nonlinearity caused by sample damage in the nonlinear imaging technique with phase object

The nonlinear imaging technique with phase object(NIT-PO)is a newly developed one-laser-shot technique used to measure the third-order nonlinearity of materials.When NIT-PO is used to measure thin film materials,some of them will generate pseudo nonlinear images after being exposed to high intensity laser.The pseudo nonlinear images here means that whatever the laser intensity is,the experimental results of measured materials always exhibit image patterns similar to the ones of nonlinear sample under high intensity laser.The reasons to form the pseudo nonlinear images were researched in this paper based the experimental results of different kinds of thin film materials.Based on large number of experiments,we consider that the pseudo nonlinear images are induced by two kinds of sample damage:one is the carbonization or destruction(form a black spot),and the other is laser ablation or bleaching(form a white spot).Our points of view were validated by both experiments and numerical simulations.