Dipartimento di Fisica "Ettore Pancini", Università di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy.
CNR-SPIN UOS Napoli, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy.
Sci Rep. 2017 Feb 7;7:42142. doi: 10.1038/srep42142.
In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams.
在过去的几年中，具有不同偏振状态空间分布（例如，方位角、径向、螺旋等）的飞秒光学涡旋光束已被用于在不同材料上生成复杂、规则的表面图案。在这里，我们展示了一种基于 q 板产生的更大一类矢量光束的飞秒激光直接表面结构化的实验研究，q 板的拓扑电荷 q=+1/2。实际上，通过电压调谐 q 板光延迟，可以在焦平面中产生偏振和强度分布具有连续空间演化的一系列超短激光光束。这些光束可以被认为是具有均匀偏振的高斯光束和具有径向或方位角偏振状态的涡旋光束的受控相干叠加。在表面结构化中使用这种超短激光光束系列可以进一步扩展可实现的表面图案。将矢量光束特性在焦平面上的理论预测与生成的表面图案进行比较，用于合理化表面结构对激光束局部状态的依赖关系，从而为设计非常规表面结构或诊断复杂超短激光束提供了一种有效的方法。
