Intensity pump effects in the kinetics of I-4(11 2) level in ErAG

A detailed analysis of the non-exponential behaviour of the kinetics of the initial laser level for three-micrometer generation I-4(11 2), in ErAG (Erbium Aluminium Garnet) crystals (laser transition I-4(11 2) -- I-4(13 2)), excited in the H-2(11 2) level with short laser pulses of variable intensity, is performed. The observed non-exponentiality of the I-4(11 2) decay and its dependence on the energy of the exciting pulse cannot be satisfactorily described with a rate equation modelling which includes only two-ion energy transfer processes among Er3+ ions as up-conversion from the terminal laser level (I-4(13 2)), up-conversion from the initial one, and cross-relaxation from I-4(9 2) and S-4(3 2) (thermalised, at room temperature, with H-2(11 2)). Our analysis has shown that the inclusion of three-ion up-conversion processes from both initial and terminal three-micrometer laser levels leads to an excellent agreement between experimental and theoretical non-exponentiality of the I-4(11 2) decay for various pumping intensities and allows the estimation of the three-ion up-conversion rates. (C) 1998 Elsevier Science B.V. All rights reserved.