Passive Q switching and mode-locking of Er:glass lasers using VO2 mirrors

Abstract

Passive Q switching of an Er:glass laser with the pulse width varying between 14 and 80 ns has been demonstrated, using three resonator vanadium‐dioxide‐coated (VO₂) mirror samples with temperature‐dependent reflectivity and differing in the reflectivity contrast. The reflectivity changes because of a phase transition from a semiconductor to a metallic state. Broad band operating characteristics of VO₂ mirrors provide Q switching over a wide range of wavelengths. In addition, mode‐locked pulses with much shorter time scales have been observed, due to exciton formation and recombination. A simple criterion is derived for the allowable ambient temperatures at which the Q switching operates effectively. A simple relation has also been found relating the duration of the Q‐switched pulse to the contrast in reflectivities of the two mirror phases.