Ultrafast Cylindrical Vector Beams for Improved Energy Feedthrough and Low Roughness Surface Ablation of Metals

Abstract

The use of ultrafast cylindrical vector vortex beams in laser–matter interactions permits new ablation features to be harnessed from inhomogeneous distributions of polarization and beam geometry. As a consequence, the ablation process can yield higher ablation efficiency compared with conventional Gaussian beams. These beams prevent surface quality degradation during the ablative processes. When processing stainless steel and titanium, the average surface roughness obtained by deploying the cylindrical vector is up to 94% lower than the Gaussian case, and the processing efficiency is 80% higher.

Transverse Spin Hall Effect and Twisted Polarization Ribbons at the Sharp Focus

“…On the axis-centered circles in the focal plane for which |T(r)| > |R(r)|, the spin density S z is positive and, vice versa, on circles where |T(r)| < |R(r)|, the spin density is negative. Thus, we have shown that at the tight focus of field (21), the sign of the longitudinal spin component S z is alternating. Assuming a positive S z on some radius in the focal plane, we find that with increasing radius, S z is decreasing before becoming zero and then negative with further increasing radius.…”

“…the optical axis, the major axis vector of the polarization ellipse in Figure 3 makes four half-turns, or two full turns. When compared to the polarization singularity index for V-point in the original plane (η = 1), a larger singularity index value at the focus for the C-point (IC = 2) is due to the fact that while in the original plane, the optical vortex topological charge (n = 1) has no effect on the singularity index of field (21), in the focal plane, the optical vortex changes the polarization pattern topology, increasing the polarization index value by 1 thanks to extra phase jumps by π.…”

“…A specific feature of light field ( 21) is that at its tight focus, the longitudinal projection of the E-vector equals zero. At the center of a linearly polarized light field (21), there is a V-point polarization singularity where the linear polarization vector is uncertain. For the V-point polarization singularity, the Poincare-Hopf index is η = 1, which means that when making a full circle about the beam center in the original plane, the linear polarization vectors make a full turn.…”

“…This effect may be called a transverse (azimuthal) spin Hall effect. 22) and putting n = 1, field (21) is seen to produce an on-axis C-point of right-handed circular polarization, with its polarization singularity index being equal to Ic = 2. Upon moving anticlockwise around the optical axis, the major axis vector of the polarization ellipse in Figure 3 makes four halfturns, or two full turns.…”

“…Figure 3 depicts intensity patterns across the focal spot generated by the initial field (21) at n = 1, with white-yellow areas marking the maximum intensity and violet-black areas showing the minimum intensity. In view of Equation (22) and putting n = 1, field(21) is seen to produce an on-axis C-point of right-handed circular polarization, with its polarization singularity index being equal to Ic = 2. Upon moving anticlockwise around the optical axis, the major axis vector of the polarization ellipse in Figure3makes four halfturns, or two full turns.…”