added 2 research items
Laser Induced Periodic Surface Structuring (LIPSS) is a powerful tool for creating sub-micrometric features on large surfaces in an up-scalable and industrial way. In order to control the process and reach a sufficient uniformity for some applications a careful attention must be paid to the control of the laser beam parameters like its polarization, stability and shape. A uni-form beam shape is mandatory in some cases. Although some demonstrations of beam shaping with high power handling optical components have been made, there is not much reported re-garding the use of SLM (Spatial Light Modulator) for beam shaping of ultrashort pulses. In the current work we show the possibility to use SLM with different type of laser sources, including a femtosecond system delivering up to 1 mJ per pulses.
Surface nanostructuring has received increasing attention in recent years due to the wide range of applications in which it offers advantages. Particularly, Laser-Induced Periodic Surface Structures (LIPSS) have proven useful for surface functionalization. LIPSS are periodic formations generated in most materials when irradiated with linearly polarized radiation. The orientation of these structures is directly linked to the polarization of the incident light, while other parameters of their morphology such as period and depth can be controlled with the number of pulses, fluence, wavelength and pulse duration of the incident light.
Birefringence induced by nanoripples generated by laser (Laser Induced Periodic Surface Structures, LIPSS), enables their use as polarization gratings. Their fabrication is simple, as LIPSS geometry is defined by the characteristics of the laser and the substrate in a one-step process. In this work LIPPS generated on stainless steel have been used to measure the change in polarization of the light reflected on them. Parameters such as period, depth or width of the ripples define the optical properties of these polarization gratings. As the fabrication parameters change, results show a gradual change in polarization. Our experiments, performed with a setup based in cylindrical focusing lens, demonstrate the fast fabrication of samples for different applications, such as waveplates.
A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4 mm/s with constant energy per pulse of 1.4 mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices.