Printing functional, metal parts for mass production using powder bed fusion additive manufacturing requires the ability to deposit more energy at the working plane to increase build rate. Conventional approaches serially add fiber lasers and scanners to create dual and quad laser machines, but scaling this strategy is limited by the size of powder bed while current scan parameters do not utilize the full output potential of available laser sources. Instead, a processing head containing an array of lower power laser sources can melt wider regions of a powder bed simultaneously to increase build rate. A 16 channel processing head comprised of fiber-coupled direct diodes capable of outputting up to 960W of combined power is presented. Fiber arrays arranged to melt widened tracks of CoCr powder demonstrated builds with >99% density at 2x the build rate of conventional, single laser systems. Details of the array layout, optical system and controls are presented along with scan strategies for melt tracks of varying widths. Most importantly, the array configuration can be scaled to multi-kW outputs spread over larger areas without requiring new parameter development as the energy per unit area remains unchanged with channel count.
Fiber optic cables have been successfully deployed in ocean floors for decades to enable trans-oceanic telecommunication. The impact of strain and moisture on optical fibers has been thoroughly studied in the past 30 years. Cable designs have been developed to minimize strain on the fibers and prevent water uptake. As a result, the failure rates of optical fibers in subsea telecommunication cables due to moisture and strain are negligible. However, the relatively recent use of fiber optic cables to monitor temperature, acoustics, and especially strain on subsea equipment adds new reliability challenges that need to be mitigated. This paper provides a brief overview of the design for reliability considerations of fiber optic cables for subsea asset condition monitoring (SACM). In particular, experimental results on fibers immersed in water under varying accelerated conditions of static stress and temperature are discussed. Based on the data, an assessment of the survivability of optical fibers in the subsea monitoring environment is presented.
This paper describes the development and optimization of chiral, non-polar media with large second-order nonlinear optical responses. We employ molecular engineering, quantum- mechanical sum-over-states theory, and measurements of molecular hyperpolarizability by means of Kleinman-disallowed hyper-Rayleigh scattering in order to understand molecular properties. Then we analyze the appropriate arrangement of the chromophores that produce an optimum axial nonlinear optical medium. Chromophores with large Kleinman disallowed traceless symmetric second rank tensor hyper-polarizabilities (beta) can be aligned so as to result in large susceptibilities, (chi) (2), in structures that lack polar order. We found that (Lambda) -shaped chromophores with C2v or similar symmetry are good candidates for these materials as they can exhibit large second-rank components of the hyperpolarizability tensor. A wide variety of techniques can be used to fabricate bulk materials belonging to the chiral non-polar symmetry groups, D(infinity ) and D2. The microscopic chromophore alignment schemes that optimize the NLO response in such materials are deduced from general symmetry consideration for both molecules and bulk.
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