900-mW average power and tunability from a diode-pumped 2.94-(mu)m Er:YAG oscillator

摘要

In this paper, the authors report on a diode-side-pumped Er:YAG laser that generates over 500 mW of average power at 2.94 (mu)m, and tunes over a 6 nm range centered about the 2.94-(mu)m transition. Prior to the development of the laser, diode-pumped Er:YAG lasers have been end-pumped monolithic devices that deliver (approximately)200 mW of output at 2.94 (mu)m. Much of the difficulty in obtaining higher average power from Er:YAG stems from the unfavorable lifetimes of the upper and lower laser levels, the complex state dynamics, and a low stimulated emission cross section ((sigma) (approx) 3 (times) 10(sup (minus)20) cm(sup 2)). One of the most important dynamical processes in Er:YAG is cross relaxation between neighboring Er(sup 3+) ions in the (sup 4)I(sub 13/2) level. By recycling much of the (sup 4)I(sub 13/2) population (lower laser level) into (sup 4)I(sub 11/2) (upper laser level), the cross relaxation overcomes the unfavorable lifetimes of the two levels, allowing the population inversion to be sustained. It is this cross relaxation along with thermalization of the two laser levels that allows cw oscillation on the 2.94 (mu)m line to take place. The laser that they describe here is a quasi-cw device as the approach to obtaining higher average power and limited tunability relies on side pumping with a quasi-cw InGaAs laser diode array. In this way, a higher gain-length product is generated, which is necessary for extending the tuning range of the laser, and for overcoming the higher losses associated with a discreet-element resonator.