Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

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The manufacturing industry often relies on numerical simulations to reduce the number of trial-anderror iterationsrequired during the process development to reduce costs. However, this can bedifficultin high strain rate manufacturing processes. For instance, in high-velocity impact welding, extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone.In this paper, numerical simulations were conducted using Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrangian-Eulerian (ALE) methods to investigatea high-velocity oblique impact between two metal plates. While the preliminary results show that the two methods were capable of modeling the process,a trade-off between the computational costand full prediction of the critical process parameters should beconsidered for industrial applications.

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