Measurement of upconversion in Er:YAG via z-scan

We demonstrate the use of the z-scan technique for measuring the upconversion coefficient in Er:YAG. The upconversion coefficient is found to be linearly proportional to the concentration for samples of concentration 0.5-3.0 at.%. A fit to four samples at room temperature yields a value of Cup=(2.0+/-0.5)×10−17 cm3/s/at.%. The coefficient at liquid-nitrogen temperatures is Cup=(9.5+/-2.4)×10−17 cm3/s/at.%.