纯铁氧化层的光学常数及其对激光耦合特性的影响

Optical Constants of Iron Oxide Films and the Influence on Coupling Characteristic of Laser

实验研究了大气环境下纯铁薄片样品在1 070nm连续激光辐照下的耦合特性变化规律,并通过控制激光辐照时间获得了不同反射率和氧化状态的纯铁氧化层样品。利用椭偏光谱法研究了不同氧化状态纯铁氧化层在1 070nm处的折射率和消光系数,基于椭偏反演结果和氧化层的微观形貌,提出了激光辐照下初期生成的α-Fe_2O_3氧化层等效折射率随膜厚变化的分段表征,并进一步修正了计算金属氧化层激光反射率的多光束干涉模型。利用修正后的模型计算了纯铁在激光辐照过程中的反射率变化规律,与实验结果吻合较好。

Coupling characteristic of materials under laser irradiation is an important and fundamental issue.Thermal oxidation happens on metal surface when irradiated by laser,which influences the laser coupling characteristic significantly.The coupling characteristic evolution of pure iron during laser irradiation was studied.Thin iron samples were irradiated by 1 070 nm continuous wave fiber laser in atmospheric environment.Several samples with different reflectivities and oxidation states were studied under different laser irradiation time.Optical constants,i.e.refractive index n and extinction coefficientκ,of these oxide layers were determined by the method of spectroscopic ellipsometry.Based on the measurement results and the microstructure evolution of oxidation,a thickness-varying equivalent refractive index ofα-Fe2O3 was proposed and a piecewise function was built to fit the variation.Then the widely-accepted model of laser interference in multi-layer oxide films for reflectivity calculation was modified.The reflectivity evolution of iron during laser irradiation was calculated based on the new model.The calculated results match the experimental results well.