Tang Yue, Perrie Walter, Rico Sierra David, Li Qianliang, Liu Dun, Edwardson Stuart P, Dearden Geoff
Laser Group, School of Engineering, University of Liverpool, Brownlow Street, Liverpool L69 3GQ, UK.
Laser Group, School of Mechanical Engineering, Hubei University of Technology, Wuhan 430068, China.
Micromachines (Basel). 2021 Apr 1;12(4):376. doi: 10.3390/mi12040376.
Diffractive multi-beams based on 1 × 5 and 2 × 2 binary Dammann gratings applied to a spatial light modulator (SLM) combined with a nanostructured S-wave plate have been used to generate uniform multiple cylindrical vector beams with radial and azimuthal polarizations. The vector quality factor (concurrence) of the single vector vortex beam was found to be C = 0.95 ± 0.02, hence showing a high degree of vector purity. The multi-beams have been used to ablate polished metal samples (Ti-6Al-4V) with laser-induced periodic surface structures (LIPSS), which confirm the polarization states unambiguously. The measured ablation thresholds of the ring mode radial and azimuthal polarizations are close to those of a Gaussian mode when allowance is made for the expected absolute intensity distribution of a ring beam generated from a Gaussian. In addition, ring mode vortex beams with varying orbital angular momentum (OAM) exhibit the same ablation threshold on titanium alloy. Beam scanning with ring modes for surface LIPSS formation can increase micro-structuring throughput by optimizing fluence over a larger effective beam diameter. The comparison of each machined spot was analysed with a machine learning method-cosine similarity-which confirmed the degree of spatial uniformity achieved, reaching cos > 0.96 and 0.92 for the 1 × 5 and 2 × 2 arrays, respectively. Scanning electron microscopy (SEM), optical microscopy and white light surface profiling were used to characterize and quantify the effects of surface modification.
基于1×5和2×2二元达曼光栅的衍射多光束应用于空间光调制器（SLM）并与纳米结构的S波片相结合，已被用于产生具有径向和方位角偏振的均匀多圆柱矢量光束。发现单矢量涡旋光束的矢量品质因数（并合度）为C = 0.95±0.02，因此显示出高度的矢量纯度。多光束已被用于用激光诱导的周期性表面结构（LIPSS）烧蚀抛光的金属样品（Ti-6Al-4V），这明确地证实了偏振态。当考虑到由高斯光束产生的环形光束的预期绝对强度分布时，测量的环形模式径向和方位角偏振的烧蚀阈值接近高斯模式的烧蚀阈值。此外，具有不同轨道角动量（OAM）的环形模式涡旋光束在钛合金上表现出相同的烧蚀阈值。用于表面LIPSS形成的环形模式光束扫描可以通过在更大的有效光束直径上优化能量密度来提高微结构化产量。用机器学习方法——余弦相似度——分析了每个加工光斑的比较结果，这证实了所实现的空间均匀度，对于1×5和2×2阵列，余弦相似度分别达到cos> 0.96和0.92。使用扫描电子显微镜（SEM）、光学显微镜和白光表面轮廓分析来表征和量化表面改性的效果。
