Laser microprocessing of steel with radially and azimuthally polarized femtosecond vortex pulses

Abstract

The use of a liquid-crystal spatial light modulator (SLM) device to convert a linearly polarized femtosecond laser beam into a radially or azimuthally polarized vortex beam is demonstrated. In order to verify the state of polarization at the focal plane, laser induced periodic surface structures (LIPSS) are produced on stainless steel, imprinting the complex vectorial polarization structures and confirming the efficacy of the SLM in producing the desired polarization modes. Stainless steel plates of various thicknesses are micromachined with the radially and azimuthally polarized vortex beams and the resulting cut-outs are analysed. The process efficiency and quality of each mode are compared with those of circular polarization. Radial polarization is confirmed to be the most efficient mode for machining high-aspect-ratio (depth/width > 3) channels thanks to its relatively higher absorptivity. Following our microprocessing tests, liquid-crystal SLMs emerged as a flexible off-the-shelf tool for producing radially and azimuthally polarized beams in existing ultrashort-pulse laser microprocessing systems.

Ripple formation on nickel irradiated with radially polarized femtosecond beams

“…Laser beams with cylindrical polarization states, namely radial and azimuthal polarization, have gained remarkable attention in the past two decades, as the symmetry of the polarization enables new processing strategies [1] with applications in various fields including microscopy, lithography [2], electron acceleration [3], material processing [1,4,5] and optical trapping [6]. The so-called cylindrical vector beams (CVB) have been the topic of numerous theoretical and experimental investigations [4,[7][8][9][10].…”

Generation of Femtosecond Optical Vortex Beams in All-Fiber Mode-Locked Fiber Laser Using Mode Selective Coupler

“…As vortex beams have a phase singularity, they have a doughnut-shaped spatial profile with zero intensity at the center. Due to the doughnut spatial structure and OAM properties, optical vortex beams attract a lot of attention in view of their applications, including optical tweezers [3], particle trapping [4], high precision micromachining [5], [6], quantum computation [7], data transmission [8], optical communications [9]- [11] and material processing [12]- [16].…”

Generation and double-slit interference of higher-order vector beams

“…For example, the radially polarized (RP) beam has a cylindrical symmetry during polarization, which enables it to provide a sharper focused spot beyond the diffraction limit when focused by a high numerical aperture lens; additionally, there is a strong longitudinal electric field component with a nonpropagating component in the focus [2][3][4]. The vector beams have been widely used in particle guiding, accelerating [5] and trapping [6,7], metal microprocessing [8,9], optical data storing [10], and high resolution microscopy applications [11,12].…”