Z-scan Measurement of Upconversion in Er:YAG

Cooperative, or energy-transfer, upconversion reduces the population of the I13/2 manifold in Er:YAG, increasing the laser threshold, but not, in theory, the slope efficiency [1]. We have measured the cooperative upconversion parameter in Er:YAG using the z-scan technique as a function of Er concentration (0.5% to 5%) with the sample at room temperature (298 K) and 80 K. The value we obtain at room temperature is 2-3 times larger than previously reported [2,3]. The value we obtain at 80 K is approximately eight times larger than the value at room temperature.