Generation of Kerr combs centered at 4.5 µm in crystalline microresonators pumped with quantum-cascade lasers.

We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 µm, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8).

Narrowband Er:YAG nonplanar ring oscillator at 1645 nm.

We report 1645 nm narrowband operation of a monolithic Er:YAG nonplanar ring oscillator resonantly pumped at 1532 nm. Unidirectional cw power up to 0.5 W was obtained with a measured linewidth of 21 kHz.

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.