Vector Beams with Parabolic and Elliptic Cross-Sections for Laser Material Processing Applications

Beam profile engineering, where a desired optical intensity distribution can be generated by an array of phase shifting (or amplitude changing) elements is a promising approach in laser material processing. For example, a spatial light modulator (SLM) is a dynamic diffractive optical element allowing for experimental implementations of controllable beam profile. Scalar Mathieu beams have elliptical intensity distribution perceivable as optical knives in the transverse plane and scalar Weber beams have a parabolic distribution, which enables us to call them optical shovels. Here, we introduce vector versions of scalar Mathieu and Weber beams and use those vector beams as a basis to construct controllable on-axis phase and amplitude distributions with polarization control. Further, we generate individual components of optical knife and shovel beams experimentally using SLMs as a toy model and report on our achievements in the control over the beam shape, dimensions and polarization along the propagation axis

Dielectric materials volume and surface processing using femtosecond vortex beam

We demonstrate the possibility to modify dielectric materials (borosilicate glass) surface and volume using tightly focused femtosecond vortex beams (with different topological charge m = 1; m = 2; m = 3; m = 5; m = 10; m = 25) formed by computer generated amplitude holograms. By controlling femtosecond vortex beam (λ=1030 nm) waist position [...]z, number of incident pulses N, topological charge m and pulse energy Ep we get different structures induced: from micron-size ring-shaped to nanosized structures

Laguerre-Gaussian quasi-modal q-plates from nanostructured glasses

A quasi-modal version of the recently introduced Laguerre-Gaussian modal q-plates [Rafayelyan and Brasselet, Opt. Lett. 42, 1966–1969 (2017)] is proposed and implemented using femtosecond direct laser writing of space-variant nanogratings in the bulk of silica glass. The corresponding design consists of linear azimuthal modulation of the optical axis orientation and polynomial radial modulation of the retardance profile. Experimental demonstration is made for Laguerre-Gaussian modes with azimuthal indices l =(1, 2, 3) and radial index p = 0. Such quasi-modal q-plates overcome previous limitations regarding the robustness of modality against the handedness of the incident circular polarization state.Traitement hyperspectral du moment angulaire orbital de la lumièr

Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass

We demonstrate the generation of optical vortices with radial or azimuthal polarization using a space variant polarization converter, fabricated by femtosecond laser writing of self-assembled nanostructures in silica glass. Manipulation of the induced form birefringence is achieved by controlling writing parameters, in particular, the polarization azimuth of the writing beam. The fabricated converter allows switching from radial to azimuthal polarization by controlling the handedness of incident circular polarization

Three-dimensional modeling of the heat-affected zone in laser machining applications

Thermal load as well as its three-dimensional (3D) spatial distribution has been estimated inside representative materials: glass (low thermal diffusion), silicon (semimetal properties), and sapphire (a crystalline dielectric of a high thermal conductivity) for typical laser processing and direct laser writing applications. The 3D temperature distribution allows to calculate thermal stress around the focal region. This provides an assessment tool for optimization of laser microprocessing conditions for controlled laser dicing and cutting applications

Towards the generation of broadband optical vortices: extending the spectral range of a q-plate by polarization-selective filtering

Optical vortex beams in the visible and near-infrared spectrum over a wide spectral region are generated by a single S-waveplate polarization converter using polarization-selective filtering. A spectral coverage of 600 nm is demonstrated, with maximum efficiency at a wavelength of 530 nm. The broadband coverage is obtained using polarization filtering, which is applicable for any component based on geometric phase retardation. The efficiency of the filtering varies from 50% to 95% depending on the wavelength. This technique has potential application in stimulated emission microscopy and lithography