A new method for high resolution curvature measurement applied to stress monitoring in thin films

By combining the well-known grid reflection method with a digital image correlation algorithm and a geometrical optics model, a new method is proposed for measuring the change of curvature of a smooth reflecting substrate, a common reporter of stress state of deposited layers. This tool, called Pattern Reflection for Mapping of Curvature (PReMC), can be easily implemented for the analysis of the residual stress during deposition processes and is sufficiently accurate to follow the compressivetensile-compressive stress transition during the sputtering growth of a Ag film on a Si substrate. Unprecedented resolution below 10-5m-1can be reached when measuring a homogeneous curvature. A comparison with the conventional laser-based tool is also provided in terms of dynamical range and resolution. In addition, the method is capable of mapping local variations in the case of a non-uniform curvature as illustrated by the case of a non-homogeneous Mo film under high compressive stress. PReMC offers interesting perspectives for in situ accurate stress monitoring in the field of thin film growth.

Subthreshold Micropulse Laser vs. Conventional Laser for Central Serous Chorioretinopathy: A Randomized Controlled Clinical Trial

Purpose: To investigate the effectiveness and safety of 577-nm subthreshold micropulse laser (SML) on acute central serous chorioretinopathy (CSC).Methods: One hundred and ten patients with acute CSC were randomized to receive SML or 577-nm conventional laser (CL) treatment. Optical coherence tomography and best-corrected visual acuity (BCVA) were performed before and after treatment.Results: At 3 months, the complete resolution of subretinal fluid (SRF) in 577-nm SML group (72.7%) was lower than that in CL group (89.1%) (Unadjusted RR, 0.82; P = 0.029), but it was 85.5 vs. 92.7% at 6 months (unadjusted RR, 0.92; P = 0.221). The mean LogMAR BCVA significantly improved, and the mean central foveal thickness (CFT) significantly decreased in the SML group and CL group (all P < 0.001) at 6 months. But there was no statistical difference between the two groups (all P > 0.05). In the SML group, obvious retinal pigment epithelium (RPE) damage was shown only in 3.64% at 1 month but 92.7% in the CL group (P < 0.001).Conclusions: Although 577-nm SML has a lower complete absorption of SRF compared with 577-nm CL for acute CSC at 3 months, it is similarly effective as 577-nm CL on improving retinal anatomy and function at 6 months. Importantly, 577-nm SML causes less damage to the retina.

Development of micromirror-based laser line generator

A laser line generator projects a straight line on an object and is widely used for alignment, identification, barcode reading, etc. Conventional laser line generators make use of cylindrical and Powell lenses that convert a laser beam spot into a line. Because of a fixed fan angle, however, the length and brightness of the generated line depends on the working distance between the laser module and object. In this project, using the optical system design software Zemax and engineering CAD software Solidworks, a micromirror based laser line generator is designed and fabricated. The performance of the fabricated micromirror based laser line generator is tested and compared with the performance of a conventional laser line generator. The results show that the length and brightness of image line can be kept constant by the designed generator.

Development of micromirror-based laser line generator

A laser line generator projects a straight line on an object and is widely used for alignment, identification, barcode reading, etc. Conventional laser line generators make use of cylindrical and Powell lenses that convert a laser beam spot into a line. Because of a fixed fan angle, however, the length and brightness of the generated line depends on the working distance between the laser module and object. In this project, using the optical system design software Zemax and engineering CAD software Solidworks, a micromirror based laser line generator is designed and fabricated. The performance of the fabricated micromirror based laser line generator is tested and compared with the performance of a conventional laser line generator. The results show that the length and brightness of image line can be kept constant by the designed generator.

An Autonomous Laser Kirigami Method With Low-Cost Real-Time Vision-Based Surface Deformation Feedback System

We introduce an autonomous laser kirigami technique, a novel custom manufacturing machine system which functions somewhat similar to a photocopier. This technique is capable of creating functional freeform shell structures using cutting and folding (kirigami) operations on sheet precursors. Conventional laser kirigami techniques are operated manually and rely heavily on precise calibrations. However, it is unrealistic to design and plan out the process (open loop) to realize arbitrary geometric features from a wide variety of materials. In our work, we develop and demonstrate a completely autonomous system, which is composed of a laser system, a 4-axis robotic arm, a real-time vision-based surface deformation monitoring system, and an associated control system. The laser system is based on the Lasersaur, which is a 120-Watt CO2 open source laser cutter. The robotic arm is employed to precisely adjust the distance between a workpiece and the laser lens so that a focused and defocused laser beam can be used to cut and fold the workpiece respectively. The four-axis robotic arm provides flexibility for expanding the limits of possible shapes, compared to conventional laser machine setups where the workpiece is fixed on rigid holders. The real-time vision-based surface deformation monitoring system is composed of four low-cost cameras, an integrated AI-assisted algorithm, and the sensors (detachable planar markers) mounted on the polymer-based sheet precursors, and allows real-time monitoring of the sheet forming process and geometric evolution with a geometric feature estimation error less than 5 % and delay time around 100ms. The developed control system manages the laser power, the laser scanning speed, the motion of the robotic arm based on the designed plan as well as the close-loop feedback provided by the vision-based surface deformation monitoring system. This cyber-physical kirigami platform can operate a sequence of cutting and folding processes in order to create kirigami objects. Hence, complicated kirigami design products with various different polygonal structures can be realized by undergoing sequential designed laser cuts, and bends (at any folding angles within designed geometric tolerance) using this autonomous kirigami platform.

Low-Power Laser Micro-Shaping of Dye-Volatile Cocrystals: The Gentle Cutting Edge of Photoresponsive Materials

Cocrystallisation of a fluorinated azobenzene with volatile cocrystal components dioxane or pyrazine yields halogen-bonded cocrystals that can be cut, carved or engraved with low-powered visible laser light. This process, termed cocrystal laser micro-shaping (CLMS), is enabled by cocrystallisation of a visible light dye with a volatile component, giving rise to materials that can be selectively disassembled with micrometer precision using gentle, non-burning irradiation in a commercial confocal microscope setup. The ability to shape and even machine cocrystals in 3D using laser powers between 0.5 and 20 mW, which are 2-4 orders of magnitude lower compared to laser powers used for machining metals, ceramics or polymers, is rationalized by CLMS targeting the disruption of weak supramolecular interactions between cocrystal components, rather than the breaking of covalent bonds in polymers or disruption of ionic structures required for conventional laser beam or focused ion beam machining processes, mainly by high-power laser heating.<br>

Low-Power Laser Micro-Shaping of Dye-Volatile Cocrystals: The Gentle Cutting Edge of Photoresponsive Materials

Cocrystallisation of a fluorinated azobenzene with volatile cocrystal components dioxane or pyrazine yields halogen-bonded cocrystals that can be cut, carved or engraved with low-powered visible laser light. This process, termed cocrystal laser micro-shaping (CLMS), is enabled by cocrystallisation of a visible light dye with a volatile component, giving rise to materials that can be selectively disassembled with micrometer precision using gentle, non-burning irradiation in a commercial confocal microscope setup. The ability to shape and even machine cocrystals in 3D using laser powers between 0.5 and 20 mW, which are 2-4 orders of magnitude lower compared to laser powers used for machining metals, ceramics or polymers, is rationalized by CLMS targeting the disruption of weak supramolecular interactions between cocrystal components, rather than the breaking of covalent bonds in polymers or disruption of ionic structures required for conventional laser beam or focused ion beam machining processes, mainly by high-power laser heating.<br>