Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues

The cw and Q-switched performance of Er:YAG lasers operating at 1645 nm were measured. Guided by previous work in the literature, we sought to improve efficiency at low pulse repetition frequencies by decreasing the doping level from 0.5 to 0.25 at. % to reduce upconversion losses. Only a small improvement was obtained with this first-time-tested lower-doped material. Measurements of the fluorescence due to upconversion directly indicated that loss due to this process could not account for the observed power loss at low pulse repetition frequencies. Enhanced green emission during Q-switched operation, resulting from two-photon absorption of 1645 nm intracavity laser light, is reported for what we believe to be the first time. Measurements indicated that the output loss from this process is negligible. (C) 2009 Optical Society of America