Abstract

Pump-induced heating of the laser gain media could considerably limit the performance of the laser/amplifier systems due to temperature-dependent dynamics such as thermal quenching of fluorescence lifetime, thermal lensing, and thermally induced stress. Hence, accurate determination of temperature distribution inside the laser crystals is quite important for understanding and surpassing the limitations of thermal effects. This in turn requires accurate knowledge of fractional thermal load (FTL) created by the pump beam in the laser crystal. It is possible to estimate FTL indirectly via investigating the variation of crystal temperature or thermal lensing with absorbed pump power level, but these indirect methods require accurate knowledge of the other system parameters such as thermal conductivity and thermo-optic coefficient [1]. Direct measurement of the fractional thermal load in Yb:YAG and Nd:YAG has been reported using laser calorimetry at room temperature but only in non-lasing conditions [2]. In this work, to the best of our knowledge, we will report directly measured FTL values for Yb:YLF and Yb:YAG materials under lasing conditions and at cryogenic temperatures for the first time.

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