Novel non-stoichiometric Co2+: spinel passive Q-switch

The development of an alumina-rich cobalt-doped spinel saturable absorber for the passive q-switching of 1530-1555 nm lasing is reported(1). This optimized composition results in crystals with excellent dopant uniformity that are highly manufacturable. The crystal growth and materials characterization are described as well as initial passive q-switch testing of the material. The single crystals grown and investigated crystallized in the Fd3m space group and have the formula Mg1-xCoxAlyOz where x is greater than 0 and less than 1, y is greater than 2 and less than about 8, and z is between about 4 and 13. Comparison data of stoichiometric spinel MgAl2O4 and alumina-rich non-stoichiometric spinel MgAl6O10 are presented. The spinel lattice is comprised of octahedral and tetrahedral cationic sites, and in the alumina-rich spinel essentially all of the magnesium and cobalt occupy tetrahedral sites. The alumina-rich cobalt-doped spinel studied exhibited uniform cobalt-dopant distribution throughout the crystal and desirable mechanical and physical properties. Q-switched pulses were produced using the alumina-rich Co2+ :MgAl6O10 saturable absorber in a 980 nm diode-pumped Yb:Er:glass solid-state-laser operating at 1543 nm. The q-switching established employed the T-4(i) absorption band of the Co2+ : MgAl6O10 and with quasi-CW pumping, pulsewidths greater than 20 ns, pulse energies of greater than 250 mu J, and free-running pulse repetition frequencies (PRFs) up to 1.2 kHz were demonstrated.