Laser-induced surface modifications for optical applications

Surface treatments by applying laser processing have gained a significant attention due to the achievable surface properties along with the selectivity that cannot be realized with other methods. The focus of this research is on investigating and developing laser-based treatment methods, i.e. laser-induced surface oxidation, laser-induced oxygen reduction, and laser-induced periodic surface structures (LIPSS), to address the requirements of specific applications in optics, aesthetics, and anti-counterfeiting, e.g. colour marking and the fabrication of optical devices and diffraction holograms. A single spot oxidation method is proposed to control the size of the oxidation area and its thickness on titanium substrates. A pixel resolution down to the beam spot size with high special control is achieved. To produce diffraction optical devices on glass substrates a direct writing another method is proposed. Especially, the method is implemented and validated for fabricating two-level phase-type FZPs with a nanosecond laser by converting a titanium film on glass substrates into titanium dioxide patterns with a thickness controlled at nano scale. The flexibility and applicability of laser-induced oxidation is extended with a method for erasing colour marks selectively by employing a laser-induced oxygen reduction. Finally, a method for producing LIPSS patterns with varying orientations is developed and then validated for fabricating diffraction gratings on metallic surface

Micromechanical Modelling of the Deformation and Damage Behaviour of Al6092/SiC Particle Metal Matrix Composites

To enhance the performance and design of metal matrix composites, it is extremely important to gain a better understanding of how the microstructure influences the deformation and damage behaviour of metal matrix composites under different loading conditions. Finite element (FE) analysis can be used to collect certain micromechanical information of composites that is difficult to obtain from experiments. In this work, the effect of the distance between the SiC particles and the loading conditions on the deformation and damage behaviour of Al6092/SiC particle composites is investigated under different strain rates (i.e., 1x10-4 , 2x10-4 , and 4x10-4 s-1). A program is developed to generate the 2D micromechanical FE model with 17.5Vol. % SiC particles. Based on the scanning electron microscopy (SEM) images, the FE model contains four SiC particle sizes (3.1, 4.46, 6.37, and 9.98 μm) with various percentages, which are randomly distributed in the micromechanical Al6092 alloy matrix. User-defined field (USDFLD) subroutine was developed and implemented through Abaqus/Standard based on maximum principal stress and Rice-Tracey triaxial damage indicator to evaluate the formability of the aluminium matrix composite (AMC) and to predict the brittle and ductile fracture of the SiC particles and the aluminium matrix, respectively, under tensile and shear loads. The results showed that the distribution of SiC particles in Al matrix has a significant effect on the mechanical properties of Al6092/SiC 17.5 particle composites. The formability and damage behaviour of composites improve as particle distance increases and strain rate decreases under tensile and shear loading. The fracture initiation toughness of fine SiC particles is higher than that of coarse SiC particles

Carbon Nanotube Array Based Binary Gabor Zone Plate Lenses

Diffractive zone plates have a wide range of applications from focusing x-ray to extreme UV radiation. The Gabor zone plate, which suppresses the higher-order foci to a pair of conjugate foci, is an attractive alternative to the conventional Fresnel zone plate. In this work, we developed a novel type of Beynon Gabor zone plate based on perfectly absorbing carbon nanotube forest. Lensing performances of 0, 8 and 20 sector Gabor zone plates were experimentally analyzed. Numerical investigations of Beynon Gabor zone plate configurations were in agreement with the experimental results. A high-contrast focal spot having 487 times higher intensity than the average background was obtained

Micromechanical Modeling of the Deformation and Damage Behavior of Al6092/SiC Particle Metal Matrix Composites

To enhance the performance and design of metal matrix composites, it is extremely important to gain a better understanding of how the microstructure influences the deformation and damage behaviour of metal matrix composites under different loading conditions. Finite element (FE) analysis can be used to collect certain micromechanical information of composites that is difficult to obtain from experiments. In this work, the effect of the distance between the SiC particles and the loading conditions on the deformation and damage behaviour of Al6092/SiC particle composites is investigated under different strain rates (i.e., 1x10-4 , 2x10-4 , and 4x10-4 s-1). A program is developed to generate the 2D micromechanical FE model with 17.5Vol. % SiC particles. Based on the scanning electron microscopy (SEM) images, the FE model contains four SiC particle sizes (3.1, 4.46, 6.37, and 9.98 μm) with various percentages, which are randomly distributed in the micromechanical Al6092 alloy matrix. User-defined field (USDFLD) subroutine was developed and implemented through Abaqus/Standard based on maximum principal stress and Rice-Tracey triaxial damage indicator to evaluate the formability of the aluminium matrix composite (AMC) and to predict the brittle and ductile fracture of the SiC particles and the aluminium matrix, respectively, under tensile and shear loads. The results showed that the distribution of SiC particles in Al matrix has a significant effect on the mechanical properties of Al6092/SiC 17.5 particle composites. The formability and damage behaviour of composites improve as particle distance increases and strain rate decreases under tensile and shear loading. The fracture initiation toughness of fine SiC particles is higher than that of coarse SiC particles

Fabrication of TiO2 Thin Film Based Fresnel Zone Plates by Nanosecond Laser Direct Writing

Fresnel zone plates (FZPs) have been gaining a significant attention by industry due to their compact design and light weight. Different fabrication methods have been reported and used for their manufacture but they are relatively expensive. This research proposes a new low-cost one-step fabrication method that utilizes nanosecond laser selective oxidation of titanium coatings on glass substrates and thus to form titanium dioxide (TiO2) nanoscale films with different thicknesses by controlling the laser fluence and the scanning speed. In this way, phase-shifting FZPs were manufactured, where the TiO2 thin-films acted as a phase shifter for the reflected light, while the gain in phase depended on the film thickness. A model was created to analyze the performance of such FZPs based on the scalar theory. Finally, phase-shifting FZPs were fabricated for different operating wavelengths by varying the film thickness and a measurement setup was built to compare experimental and theoretical results. A good agreement between these results was achieved, and an FZP efficiency of 5.5% to 20.9% was obtained when varying the wavelength and the oxide thicknesses of the zones.</jats:p