Two-frequency Er-Yb:glass microchip laser passively Q switched by a Co:ASL saturable absorber

Passive Q switching of a two-frequency Er³⁺ -Yb³⁺:glass laser at 1.55 μm with a new Co²⁺: La_xSr_1-xMg_x-yCo_yAl_12-xO ₁₉ crystal as a saturable absorber is demonstrated. We show that, with an extended cavity setup, the beat frequency between the orthogonally polarized laser eigenstates is continuously tunable by adjustment of the retardance of an intracavity birefringence. A similarly built microchip laser emits two-frequency pulses of 6-ns duration with a beat frequency of as much as 19 GHz. Moreover, two-frequency pulses at 777 nm are obtained by second-harmonic generation in a periodically poled lithium niobate crystal. Such pulses can be useful for applications such as Doppler lidar radar.