We report the observation of modulational instability (MI) of a partially spatially incoherent beam induced by seeding noise through cross-phase modulation. We show experimentally that a threshold exists for such induced incoherent MI to occur that depends on the degree of spatial coherence as well as on the strength of the nonlinearity. Above threshold, the induced MI leads to the formation of ordered and disordered patterns of incoherent light.
We demonstrate experimentally that a periodic perturbation on a partially spatially incoherent optical beam induces modulation instability that depends strongly on the perturbation periods as well as on the strength of the nonlinearity and the degree of spatial coherence. At a fixed value of the nonlinearity and coherence, the incoherent modulation instability has a maximum growth at a preferred perturbation period (or spatial frequency), leading to the formation of ordered patterns. While the nonlinearity in our photorefractive system is inherently anisotropic, pattern control and pattern switching with anisotropic coherence is readily realized. Our experimental observations are in good agreement with theoretical predictions.
As future land-based gas turbine engines are being designed to operate with inlet temperatures exceeding 1300°C (2370°F), efforts at NETL have been focused on developing advanced materials systems that are integrated with novel airfoil cooling architectures. Recent achievements in the areas of low cost diffusion bond coat systems applied to single- and poly-crystalline nickel-based superalloys, as well as development of thin nickel-based oxide dispersion strengthened layers are presented in this paper. Integration of these material systems with commercially cast, novel, pin-fin internal cooling airfoil arrays, tripod film cooling hole architectures, trailing edge cooling geometries, and near surface micro-channel concepts is also presented.
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