Abstract

A detailed analysis of the non-exponential behaviour of the kinetics of the initial laser level for three-micron generation ⁴I_11/2, in ErAG (Erbium Aluminium Garnet) crystals (laser transition ⁴I_11/2 →⁴I_13/2), excited in the ⁴H_11/2 level with short laser pulses of variable intensity, is performed. The observed non-exponentiality of the ⁴I_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 (⁴I_13/2), up-conversion from the initial one. and cross-relaxation from ⁴I_9/2 and ⁴S_3/2 (thermalised, at room temperature, with ²H_11/2) Our analysis has shown that the inclusion of three-ion up-conversion processes from both initial and terminal three-micron laser levels leads to an excellent agreement between experimental and theoretical non-exponentiality of the ⁴I_11/2 decay for various pumping intensities and allows the estimation of the three-ion up-conversion rates The best agreement with the experimental non-exponentialities was obtained ω₁₁₁ = ω₂₂₂ = 2 x 10^-34 cm⁶s^-1 and q₂ = 0.9, where ω₁₁₁ and ω₂₂₂ represent the rates of three-ion upconversion from ⁴I_13/2 and ⁴I_11/2, respectively, and q₂ is the ratio o two-ion up-conversio rates.

© 1998 IEEE