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 beam is demonstrated. The influence of each polarization on various aspects of ultra-short pulse laser micro-processing is discussed. For the first time, Laser Induced Periodic Surface Structures (LIPSS) were produced on stainless steel using these modes of polarization, imprinting the complex polarization vector structures at the focal point of a low numerical aperture objective. Micro-machining stainless steel plates of various thicknesses is investigated. Analysing the resulting cut-outs reveals the specific properties of machining with radial and azimuthal polarizations. The process efficiency and quality of each mode are compared with those of circular polarization. Radial polarization is confirmed as the most efficient mode for coupling laser energy into the material, ablating more material overall than azimuthal or circular polarizations. Thanks to their high absorptivity, radially polarized beams are found to produce more ablation in the upper parts of the machined structures. Because of their higher reflectivity, azimuthally polarized beams are more efficient to channel laser energy to the bottom of deep structures, making them best suited for machining high aspect-ratio structures. Following our micro-processing tests, cylindrical polarizations such as radial or azimuthal are confirmed to be powerful tools in laser engineering. Depending on the aspect-ratio of the machined structures, radial or azimuthal polarization is most suited. Liquid crystal SLMs emerged as a flexible off-the-shelf tool for generating radial and azimuthal polarized beams in existing ultra-short pulse laser systems.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 beam is demonstrated. The influence of each polarization on various aspects of ultra-short pulse laser micro-processing is discussed. For the first time, Laser Induced Periodic Surface Structures (LIPSS) were produced on stainless steel using these modes of polarization, imprinting the complex polarization vector structures at the focal point of a low numerical aperture objective. Micro-machining stainless steel plates of various thicknesses is investigated. Analysing the resulting cut-outs reveals the specific properties of machining with radial and azimuthal polarizations. The process efficiency and quality of each mode are compared with those of circular polarization. Radial polarization is confirmed as the most efficient mode for coupling laser energy into the material, ablating more material overall than azimuthal or circular polarizations. ...
Published Version
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