An analytical model of cw quasi-three-level lasers that includes the influence of energy-transfer upconversion (ETU) has been developed. The results of the general output modeling were applied to a laser with Gaussian beams, and rigorous numerical calculations have been made to study the influence of ETU on threshold, output power, spatial distribution of population-inversion density, and fractional thermal loading. The model was applied to a laser operating at 946 nm in Nd:YAG, where the dependence of laser-beam size on laser performance was investigated in particular. A simple model for the degradation of laser-beam quality from a transversally varying saturated gain is proposed that is in good agreement with measurements of the laser in a plane-plane cavity.
By pumping with a cw diode-pumped Nd:YAG laser operating at 946nm laser operation of a new Yb-doped phosphate glass with 440mW cw output power and a slope efficiency of 48% with respect to the absorbed pump power was achieved at room temperature.
Laser performance of a diode-pumped Nd-doped multimode phosphate-glass fiber is reported. The selection of the fundamental mode in a multimode fiber is demonstrated, resulting in laser emission that is close to diffraction limited and that is nearly independent of the pump power. The heavily Nd-doped fibers with core diameters of 100 microm and lengths between 13 and 32 mm deliver as much as 130 mW of cw output power at 1.053 microm. A total efficiency of 31% with respect to launched pump power has been achieved.
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