Most previous studies have employed surface patterning to improve the performance of lubrication systems. However, few have experimentally analyzed improved effects on friction reduction in SiC mechanical seals by ultra-fast laser pulse texturing. This work applies surface texturing on a non-contact mechanical seal and analyzes the characteristics of the resultant surface morphology. A femtosecond laser system is employed to fabricate micro/nanostructures on the SiC mechanical seal, and generates microscale-depth stripes and induces nanostructures on the seal surface. This work examines the morphology and cross section of the SiC nanostructures that correspond to the different scanning speeds of the laser pulse. Results show that varying the scanning speed enables the application of nanostructures of different amplitudes and widths on the surface of the seal. The friction coefficient of the introduced SiC full-textured seal is about 20% smaller than that of a conventional SiC mechanical seal. Hence, femtosecond laser texturing is effective and enables direct fabrication of the surface micro/nanostructures of SiC seals. This
We have conducted experimental investigations for the micromachining of dielectrics (fused silica) using an integrated femtosecond (fs) and nanosecond (ns) dual-beam laser system at different time delays between the fs and ns pulses. We found that the maximum ablation enhancement occurs when the fs pulse is shot near the peak of the ns pulse envelope. Enhancements up to 13.4 times in ablation depth and 50.7 times in the amount of material removal were obtained, as compared to fs laser ablation alone. The fs pulse increases the free electron density and changes the optical properties of fused silica to have metallic characteristics, which increases the absorption of the ns laser energy. This study provides an opportunity for efficient micromachining of dielectrics.
Solar-tracking concentrators can potentially lead to low-cost photovoltaic modules that minimize the use of costly semiconductor materials by improving optical collection and coupling. However, solar concentrators and accompanying trackers have proven to be expensive, bulky, and heavy, thereby resulting in increased balance-of-system costs. Here we demonstrate a lightweight and low-profile, and potentially low-cost planar solar-tracking concentrator based on the ancient Japanese art of origami. The tightly packed hexagonal concentrator and tracker arrays are fabricated by cutting and folding thin reflecting sheets that capture and direct concentrated light onto a small, high-efficiency GaAs solar cell. The tracker enables single-axis solar tracking via a simple one-dimensional translational motion of an actuator with minimal energy expense (∼2.9 J/ m 2 /day). Further, we demonstrate stable operation over 10 000 cycles. The solar concentrated cell achieves a 450% increase in diurnal energy output compared with an equivalent, unconcentrated cell. The potentially low cost and low profile of the origami concentrators may lead to their wide deployment on rooftops and other building-integrated applications.
This paper reports using femtosecond laser marker to fabricate the three-dimensional interior microstructures in one closed flow channel of plastic substrate. Strip-like slots in the dimensions of 800 μm×400 μm×65 μm were ablated with pulse Ti:sapphire laser at 800 nm (pulse duration of ∼120 fs with 1 kHz repetition rate) on acrylic slide. After ablation, defocused beams were used to finish the surface of microstructures. Having finally polished with sonication, the laser fabricated structures are highly precise with the arithmetic roughness of 1.5 and 4.5 nm. Fabricating such highly precise microstructures cannot be accomplished with nanosecond laser marking or other mechanical drilling methods. In addition, since laser ablation can directly engrave interior microstructures in one closed chip, glue smearing problems to damage molded microstructures possibly to occur during the chip sealing procedures can be avoided too.
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