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The detailed polarized spectroscopic investigation of math and math states of Er3+ ions in Czochralski-grown NaLa(MoO4)2 single crystals doped with Er3+ and codoped with Ce3+ as a function of cerium concentration is presented. The main results of room-temperature lifetime investigation show that the math lifetime reduces by about 50 times from the solely Er-doped sample to the crystal codoped with 50 at. % of Ce, while in the same experimental conditions, the lifetime of the math level reduces by less than two times in the most heavily Ce codoped sample. This result looks very promising from the point of view of obtaining low-threshold 1.5-μm laser oscillation

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Using a variational approach, we examine analytically the threedimensional self-trapping of Gaussian beams in a medium with higherorder nonlinearity. We Ðnd exact analytic solutions for the spot width, and the conditions under which the Gaussian beam is stable to perturbation of its spot width. We also make a comparison with a Kerr-law medium.

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