Population of excited erbium levels in Er3+:Na0.4Y0.6F2.2 (Er:NYF) laser crystals

We have studied theoretically and experimentally the population dynamics of six radiative erbium levels in concentration series of Er3+:NYF crystals. The radiative transition probabilities were calculated by the Judd–Ofelt method; the nonradiative transition probabilities were estimated; energy transfer (ET) microparameters (for migration, selfquenching (SQ), and upconversion (UC) processes) in studied crystals were estimated theoretically using the method of quantum–mechanical model calculation. The rate equations for the six lowest energy levels of erbium in Er3+:NYF crystals, including the 3μm laser transition levels, were numerically solved for the case of excitation by nanosecond pulse at λpump=1.53μm. The theoretical and experimental results for Er3+:NYF crystals are in good agreement. Single mode CW laser action was achieved in Er:NYF crystal at 2.8μm with InGaAs LD pumping of the 4I11/2 level. Output power about 72mW with slope efficiency ∼4% was achieved in longitudinal pump scheme.