High-efficiency 1064 nm nonplanar ring oscillator Nd:YAG laser with diode pumping at 885 nm.

We experimentally demonstrate a monolithic single-frequency nonplanar ring oscillator (NPRO) laser pumped by diode lasers from a thermally excited ground level directly into a metastable level of Nd:YAG gain medium. Continuous-wave output power of 4.54 W is obtained at 1064 nm with 7.6 W input at 885 nm, and the slope efficiency is 76.9% at incident power above 2 W. Compared with the 50.7% slope efficiency obtained using 808 nm pumping for the same NPRO, this direct pumping shows a potential advantage in improving the energy efficiency. The observation is consistent with an analysis of the heat generation in both direct and traditional pumping schemes. The power fluctuation is measured to be within 0.8% at 3 W output during a 10 h period.