Blue and green cw upconversion lasing in Er:YLiF₄

Two new laser transitions are reported for the Er3+ ion in YLiF4: in the blue at 469.7 nm and in the green at 560.6 nm. These are pumped with red and near-infrared laser radiation using nonlinear excitation processes in which more than one upconversion step occurs, yet the threshold pump powers are as low as 10 mW. Single longitudinal mode cw operation was observed at temperatures below 40 K. This is the first report of a blue laser using the Er3+ ion, and the first report of an infrared-pumped blue laser.