Laser-Material Interactions of High-Quality Ultrashort Pulsed Vector Vortex Beams.

Yue Tang,Stuart P Edwardson,David Rico Sierra,Walter Perrie,Geoff Dearden,Qianliang Li,Dun Liu

doi:10.3390/mi12040376

Yue Tang, Stuart P Edwardson + Show 5 more

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https://doi.org/10.3390/mi12040376

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Abstract

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.

Highlights

A meta-surface (J plate) using intracavity in a compact laser has led to direct control of the angular momentum of visible light with orbital angular momentum (OAM) quantum numbers l >100 as well as non-symmetric vector vortex beams lasing simultaneously on independent
Using Equation (1), we found fluous; Equation (1) can be simplified i the concurrence (C) for our single vector vortex beam to be C = 0.95 ± 0.02 (1σ), close to an ideal vector vortex beam, C = 1
The ablation threshold fluence for a Gaussian beam can be obtained from the equaThe ablation threshold fluence for a Gaussian beam can be obtained from the equation [33]

Summary

Introduction

The ability to create complex spatial and vector optical fields is accelerating the progress of scientific fields such as encoding information in optical communications [1], sub-diffraction high-resolution imaging [2], particle acceleration [3], improving stability of NL filamentation in dielectrics [4] and sophisticated control of light–matter interactions such as an optical spanner [5,6] Such states of light, able to carry high levels of orbital angular momentum (OAM), can be created externally from a Gaussian beam with uniform polarization by the use of spatial light modulators, spin–orbit components such as liquid crystal Q plates [7,8], nanostructured S-waveplates [9] and complex metasurfaces [10]. A meta-surface (J plate) using intracavity in a compact laser has led to direct control of the angular momentum of visible light with OAM quantum numbers l >100 as well as non-symmetric vector vortex beams lasing simultaneously on independent

Methods

Results

Conclusion