Thermally induced mode coupling in rare-earth doped fiber amplifiers

We present a simple semianalytical model of thermally induced mode coupling in multimode rare-earth doped fiber amplifiers. The model predicts that power can be transferred from the fundamental mode to a higher-order mode when the operating power exceeds a certain threshold, and thus provides an explanation of recently reported mode instability in such fiber amplifiers under high average-power operation. We apply our model to a simple step-index fiber design, and investigate how the power threshold depends on various design parameters of the fiber.     

Polymerization of ethylene with new diimine complexes of late transition metals

Three pyridylimine based complexes of Ni^II and Co^II were reacted with methylaluminoxane (MAO) and tested as catalysts in ethylene polymerization. The two nickel catalysts produced mainly methyl branched polymers with good to moderate activity, while the cobalt compound showed only marginal activity. Reaction conditions strongly affect the polymer properties, such as molecular weight, melting temperature, degree of branching, and chain end unsaturation type.