UCLA

Erbium-doped in YAG (Y3Al5O12) and in yttira (Y2O3) are the most often used laser

gain media for generation of 1.6 μm and 3 μm laser radiation. Of all the laser gain media

studied, Er-based materials are the most complicated due to the presence of rich non-linear energy transfer kinetics processes. Energy transfer upconversion (ETU) and excited state absorption (ESA) processes in Er-based laser gain materials has been investigated by many groups over the last four decades using the fluorescence decay time as an indirect measure of the ETU and ESA rates. The values reported for ETU and ESA vary two-to-three orders of magnitudes for the same materials. When attempting to model and prototype high power Er-based lasers, such a large uncertainty in the values for ETU and ESA coefficients leads to large (and sometimes unrealistic) predictions in terms of laser performance. To allow the laser community to better model and prototype high power Er-based lasers, a more accurate knowledge of ETU and ESA coefficients is needed. The objective of the present effort was to develop a faster and more accurate technique for quantifying, in absolute terms, the values for ETU and ESA coefficients in Er-based materials. The technique reported here emphasized measuring the rise and decay times of the fluorescence signal from the energy states that directly impact ETU and ESA as a function of pump wavelength and pump intensity. ETU and ESA was investigated in 0.5% and 50% single crystal and polycrystalline (ceramic) Er:YAG and 1%, 15%, and 25% polycrystalline Er:Yttria with the fluorescence signal quantified for the 4S3/2, 4F9/2, 4I9/2, 4I11/2, and 4I13/2 states. Results for the rise and fall time of the fluorescence signal in the case of 0.5% Er:YAG do not show any appreciable ETU component. This result is consistent with results already published in literature and

thus validating that the technique developed in the present study. In the case of the 50%

Er:YAG, measurements were made, which allowed the direct observation of the effects of

ESA and ETU of the 4I11/2, and 4I13/2 energy states (laser states). This technique appears to be applicable to many other rare earth ion systems.