Grayscale laser lithography is capable of producing continuous-relief (2.5D) structures down to the micro- and nanoscale for applications such as micro-optics, micro-electromechanical systems and functional surfaces. The present work evaluates build accuracy by employing benchmark artefacts having an active area of up to 1 mm × 1 mm and a structure depth of up to 50 μm with a resolution of 1 μm as models for the production of 2.5D structures with a wide range of representative features in terms of elevation, slope, curvature, aspect ratio and area density. The topography of manufactured samples is determined via laser scanning confocal microscopy and 3D optical microscopy based on white light interferometry, with alignment algorithms developed within MATLAB employed to evaluate local build error over the entire surface. Further to the incident laser energy density within each region, the applied energy in adjacent regions is found to influence build accuracy due to the laser intensity distribution, light scattering and photochemical reaction effects, with the area density and aspect ratio of model features found to be of strong influence on outcomes. The results imply that greater build accuracy can be achieved by basing process parameters on not only the local model height but also that within adjacent regions. The present work was performed within the Horizon Europe project “Automated Maskless Laser Lithography Platform for First Time Right Mixed Scale Patterning” (OPTIMAL, Grant Agreement No. 101057029), with the aim of facilitating automated approaches for error correction and accuracy optimization.
Multi-core fibers (MCFs) are promising solutions for high power fiber based devices as they reduce nonlinearity and other unwanted detrimental effects, like transverse mode instability, by transporting, instead of a single high power beam, several low-powered ones to be coherently combined at the fiber output. This method relies on accurate evaluation of the phase differences between signals in different cores, which are significantly impacted by changes in the effective index of the propagating modes. For this to be effective, spatial heat generation must be accounted for. In particular, the heat flux from the doped cores to the external boundary causes a temperature gradient across the fiber, which affects the refractive index distribution, creating the chance for effective index change and thus dephasing of the output beams, which is harmful for beam combining. The results of in-depth numerical analysis on the performance of 9-core and 16-core MCFs under thermal effects are presented by studying the mode phase sensitivity to heat load and by introducing a coupled-mode theory model to study possible optical coupling effects. The effectively single-mode condition is also investigated by calculating the core modal overlap differences between fundamental and higher-order modes.
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