Investigation of the roundtrip cavity loss in laser diode pumped erbium:ytterbium-phosphate glass microchip lasers

We present a method for determination of the roundtrip cavity loss in the laser diode pumped erbium:ytterbium-codoped phosphate glass microchip laser. Slope efficiency and laser threshold were measured in the experiment and their dependencies on roundtrip cavity loss were derived through rate equations. According to the energy levels, cumulative upconversion and cooperative upconversion are taken into consideration to ensure the accuracy of the derivation. Roundtrip cavity losses in different cavity configurations were investigated.