Abstract

Recently we reported about laser action on the 3H43H6 transition of Tm3+ ion when it is excited due to energy transfer from four-fold co-ordinated Cr4+(t) ions in YAG crystal [1,2]. 2.02 um CW oscillation was performed by 1.06 CW Nd laser pumping. The lasing threshold was about 3 W. It is correspond to 15% quantum efficiency of energy transfer from a Cr4+(t) ion to a Tm3+ ion. On the other hand the quantum efficiency was equal to 90 % by the pulsed pumping as it was obtained from measuring of Cr4+(t) luminescence relaxation time. We supported some cause reducing the quantum efficiency of energy transfer from Cr4+(t) ions to a Tm3+ ions with CW pumping. So far as an excited Tm3+ ions density, is needed for lasing, (which we estimated as 1020cm−3) is considerably higher than the Cr4+ ions concentration (it is equal to 3.1*1017 cm−3), excitation migration in Tm3+ ions system must take place after excitation transfer from a Cr4+ ion to a Tm3+ ion to reach the necessary excitation density. But a migration rate in Tm3+ system is expected lower than an excitation transfer rate from a Cr4+ to a Tm3+ ion, therefore excited Tm3+ ions will be concentrated near a Cr4+(t) being souse of excitation. So a local saturation of Tm3+ ions excitation may take place, that will cause reducing of energy transfer rate from Cr4+(t) ions to Tm3+ ions. In order to evaluate the energy transfer rate by CW pumping we had measured depandences of transmittance of YAG: YAG:Tm3+, Cr4+ and YAG:Cr4+ crystals upon the pumping power up to the power density corresponding to our lasing experiments.

© 1995 Optical Society of America

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