Laser operation with near quantum-defect slope efficiency in Nd:YVO4 under direct pumping into the emitting level

One-micron continuous-wave (cw) laser emission with 0.80 slope efficiency (0.79 optical-to-optical efficiency) under Ti: sapphire and 0.75 slope efficiency relative to absorbed power under diode-laser pumping at 880 nm into the emitting level is demonstrated in a 1-mm-thick, 1.0-at. % Nd:YVO4 crystal. These values are superior to those obtained with 809-nm pumping into the level F45/2, and can be explained consistently by the effect of the quantum defect between the pump and laser radiation, the superposition of pump and laser mode volumes, the pump-level efficiency and the residual optical losses. In the analysis of the 809-nm pumping data a pump-level efficiency equal to the unity was employed, as determined with a method based on the pump-saturation effects on absorption.