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 cosθ > 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.

Cylindrical vector vortex (CVV) beams are topical forms of structured light, and have been studied extensively as single beams, non-separable in two degrees of freedom: spatial mode and polarisation. Here we create arrays of CVV beams using a combination of dynamic phase controlled Dammann gratings and spin–orbit coupling through azimuthally varying geometric phase. We demonstrate control over the number, geometry and vectorness of the CVV arrays by simple adjustment of waveplates and computer generated holograms. To quantify the efficacy of our approach, we employ a recently proposed vector quality factor analysis, realising high quality vector beam arrays with purities in excess of 95%. Our approach is scalable in array size, robust (no interferometric beam combination) and allows for the on-demand creation of arbitrary vector beam arrays, crucial for applications that require multi-spot arrays, for example, in fast laser materials processing, multi-channel communication with spatial modes, and holographic optical traps, as well as in fundamental studies with vector optical lattices.

Laser micro-structuring of amorphous polyether(ether)ketone (PEEK) has been demonstrated with 180 fs/1 kHz NIR (775 nm) and NUV (387 nm) laser pulses. Significant differences in laser-material interaction is observed between the NIR and NUV wavelengths with single pulse ablation threshold found to be 2.01 ± 0.05 J cm⁻² and 0.23 ± 0.02 J cm⁻² at 775 nm and 387 nm respectively. This is connected to the requirement for multi-photon absorption at 775 nm, where PEEK is transparent, while at 387 nm, significant linear absorption within the material bandgap occurs, favouring sequential 2-photon absorption via reverse saturated absorption (RSA). Open aperture Z scan data yields a 2-photon absorption coefficient β ₃₈₇(I) which is intensity dependent, consistent with RSA. Multi-pulse exposure yields incubation coefficients of S₇₇₅ = 0.72 ± 0.01 and S₃₈₇ = 0.85 ± 0.02. This significant reduction in NUV incubation is consistent with a much higher level of electron excitation to the conduction band. Consequently, ablation of PEEK with NUV fs pulses is superior, exhibiting much reduced melting and re-deposition. Precision NUV polymer surface micro-structuring is accomplished while laser induced periodic surface structures (LIPSS) with pitch Λ ∼ 0.4 μm are observed at the base of ablated regions, aligned parallel to the incident polarisation. The ease of NUV LIPSS generation allowed surface patterning of large scanned areas which exhibit white light diffraction due to this sub-micron periodic surface modulation.