非柱对称飞秒矢量光在钨表面制备弧形周期条纹结构

Fabrication of Periodic Curved Ripple Structures on Tungsten Surface Using Femtosecond Non-Cylindrical Vector Beam

将两个相位光栅分别作为分束和合束元件,生成了偏振态连续变化的非柱对称飞秒矢量光束。通过调节合束相位光栅的波矢方向,即可实现标量光到矢量光的转变,以及矢量光偏振态的调节。利用非柱对称飞秒矢量光在金属钨表面制备了由弧形条纹组成的二维周期性结构,在相邻弧形条纹偏移量(水平方向的周期)保持560 nm不变的情况下,通过调节飞秒矢量光的偏振态分布,可使弧形条纹的底长(竖直方向的周期)逐渐减小至4μm。微区反射谱测量表明:弧形周期条纹的存在明显减小了可见至近红外波段的反射率,且反射率随弧形条纹底长的减小而增大。飞秒激光的辐照没有改变金属钨表面的物质组分,因此,反射率的改变完全是由钨表面的二维周期性结构导致的。

Two phase gratings are used as beam splitter and combiner to generate a femtosecond non-cylindrical vector beam exhibiting continuously varying polarizations. Further, by adjusting the orientation of the grating vector of the beam combiner, a scalar beam can be transitioned to a vector beam, and the polarization distribution of the femtosecond laser beam can be modulated. Two-dimensional periodic surface structures comprising curved ripples are fabricated on a tungsten surface using a femtosecond non-cylindrical vector beam. By adjusting the beam polarization distribution, the bottom length of the curved ripples, i.e., the period along the vertical direction, can be decreased to 4 μm while maintaining the horizontal period at 560 nm. The microreflectance spectral measurements denote that the periodic ripples significantly reduce the reflectivity in the visible and near-infrared ranges and that the reflectivity increases as the vertical period of the curved ripples decreases. Furthermore, femtosecond laser ablation does not change the chemical components of the tungsten surface, therefore, the variation in reflectance can be solely attributed to the change in surface morphology.