In lighting applications key drivers for optical design of surface textures are integration of optical elements, the disentanglement of optical functionality and appearance and late stage configuration.
We investigated excimer laser ablation as a mastering technology for micro textured surfaces, where we targeted an increase in correspondence between surface design and ablated surface for high aspect ratio structures. To achieve this we have improved the photo mask design using a heuristic algorithm that corrects for the angular dependence of the ablation process and the loss of image resolution at ablation depths that exceed the depth of field. Using this approach we have been able to demonstrate close correspondence between designed and ablated facet structures up to 75° inclination at 75 μm depth.
These facet design parameters allow for total internal reflection (TIR) as a means of beam deflection which is demonstrated in a range of mono shaped cone arrays in hexagonal tessellation. BSDF analysis was used to characterize the narrow TIR deflection beams that matched the peak positions of the design down to 28° apex. In addition, a single surface TIR-Fresnel lens design with focal distance 5 mm has been manufactured using this photo mask design algorithm and beam collimation up to 12° beam angle and 32° field angle is shown.
These outcomes demonstrate that the laser ablation process intrinsically yields sufficient small dispersion in structure and fillet radii for lighting applications.
It has been previously published how, using two separate Vertical-Cavity-Surface-Emitting-Lasers (VCSELs), a miniature laser-Doppler interferometer can be made for quasi-three-dimensional displacement measurements. For the use in consumer applications as PC-mice, the manufacturing costs of such sensors need to be minimized. This paper describes the fabrication of a low-cost laser-self-mixing sensor by integrating silicon and GaAs components using flip-chip technology. Wafer-scale lens replication on GaAs wafers is used to achieve integrated optics. In this way a sensor was realized without an external lens and that uses only a single GaAs VCSEL crystal, while maintaining its quasi-three-dimensional sensor capabilities.
A variation on the fluid jet polishing (FJP) technique, arbitrarily named Jules Verne (JV), will be described in this article. Jules Verne is a glass processing technique that removes material due to the fact that the tool and the surface are in close contact, and a slurry moves in between the tool and the surface. This approach has both advantages and disadvantages with respect to the original FJP modus: it enables a feed-controlled machining process, but deeper lying areas are harder to reach. A simulation model will be presented that predicts the flow of the slurry in the Jules Verne setup, which is followed by the computation of the trajectories of the particles in the flow. Furthermore, experimental data will be reported demonstrating the feasibility of the JV idea. A model will also be presented simulating the interaction between the surface and the impinging abrasives at a microscopic level, enabling the prediction of the final surface roughness.
The possibilities of iTIRM, an in-process surface measurement tool, are explored in this research. Experiments are done to test the applicability for qualifying and optimizing finishing processes for optical surfaces. Several optical glasses, different polishing agents and ductile grinding are included in these experiments. It is concluded that iTIRM can be used for both mentioned applications but that it is, at least for now, an R&D tool only and not applicable in production.
A prototype of a system for in-process monitoring of material removal in fluid jet polishing (FJP) is presented. The measurements make use of temporal phase unwrapping (TPU) allowing for a large working range. The measurement system will be discussed, with all problems that had to be overcome like water on the surface and vibrations, as well as the FJP system. The basics behind TPU will be presented and the first results will be shown. Finally, the capabilities of the system will be discussed. The presented system enables the in-process monitoring of the footprint as obtained by the FJP technique and measurement of the material removal rate.
This article describes the Fluid Jet Polishing process. An overview of the theoretical dependence of various important parameters is given. We discuss some results obtained with FJP, including typical material removal rates and roughness values. Some recent experiments are described that show that it is also possible to obtain removal rates as small as one nanometer per minute for glass surfaces. Specific surface profiles are created, both with and without the use of surface protecting masks.
One of the main activities of the Explosion Prevention and Protection Research Group of TNO is the quantification of explosion effects and the prediction of possible consequences. The research presented is aimed at setting up new guidelines for safety distances for urban areas around hazardous sites. To investigate the distribution of the blast load on buildings experimentally, the buildings are scaled down and exposed to a plane shockwave in a 40x40 cm2 shock tube. For perfect gasses the Hopkinson scaling law applies. This law states that if all characteristic times are scaled by the same factor as the length scale then all pressures, temperatures, densities and velocities will remain unchanged. In the shocktube the shockwave will propagate and interact with objects. The density distribution around the objects can be visualized using an interferometer and from the interferograms the pressure distribution can be computed. These data can be used to validate numerical results obtained with the Computational Fluid Dynamics code BLAST. This code, developed at the Prins Maurits Laboratory of TNO, simulates the interaction of three-dimensional blast waves with structures. The data obtained can be used for the accurate prediction of the blast load on individual buildings in an urban area. In the tests, rectangular blocks were used to obtain the two dimensional test situation shown in figure 1 .At some typical locations on the structures, the pressure signal was measured by means of piezo-resistive pressure-transducers. Interferograms were recorded using a phase-stepping double-reference-beam holographic interferometer. The principle of the interferometer setup is that the initial state and the disturbed state are both recorded on one single holographic plate, using two slightly tilted reference beams. When analyzing, the two reference beams simultaneously reconstruct the initial state and the disturbed state. The two states will interfere and the resulting interference pattern is recorded using a CCD camera. This interferometer setup is very attractive because, first of all, it is possible to record an interference pattern hardly influenced by the mechanical vibrations caused by the shock tube, secondly, this interferometer is easy to setup, and thirdly, most lens errors cancel out in the resulting image because of the double reference beam. A typical example of a reconstruction of an interferogram recorded with the holographic interferometer is shown in figure I. where the shockwave travels from the left to the right, interacting with two models of buildings. To be able to calculate tile pressure distribution, more than one reconstruction of the interferogram is needed. If the difference in optical pathlength between the reference beams is varied over an unknown, but constant, distance, at least four reconstructions are needed. From four different recordings the pressure distribution can be calculated. First, all pixels that do not have enough contrast are being removed, then the phase is calculated, for example using Carré's algorithm, the result of this can be seen in flgure 2. Subsequently the discrete 271 steps have to be removed, which is called phase unwrapping, and finally the grey values in this image have to be converted to pressure values. The resulting pattern of isobars can be seen in figure 3.This image can be compared to tile numerical simulation in figure 4 that was obtained using the BLAST-code. ibis paper presents an optical study of blast wave propagation and interaction with multiple structures and a method for obtaining quantitative information on the pressure distribution from a number of phase-stepped images.