Back-reflection Pumping Versus Contradirectional Pumping in Upconversion Solid State Lasers

We show that a change from contradirectional pumping to back-reflection pumping in upconversion lasers can reduce the threshold by 50%, increase the slope efficiency by 87%, and increase the laser output power by a factor of two to six depending on the pump powers. Our predictions are anchored to an upconversion Pr 3+ ZBLAN fiber laser experiment to within 10%.