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It has been shown, that cryogenic cooling of Yb3+-doped media is increasing laser performance significantly[1,2]. The reason for this is the thermal depopulation of the lower laser levels turning the quasi three level extraction scheme into a real four level scheme. By now most of these cryogenic cooled amplifiers aim on liquid nitrogen temperature. For future systems it has to be estimated what is an optimum operation temperature as compromise between laser performance and effort for cooling. This is needed as well from an energetic point of view as from an financial point of view. For this it is necessary to know the basic absorption and emission cross sections in dependence of temperature. We present measurement of such cross sections in an temperature range from 100K to room temperature for various gain material such as Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The absorption cross sections are calculated from the absorption spectra. The emission cross sections are determined from the absorption and emission spectra employing the Füchtbauer-Ladenburgmethod and theMcCumber relation [3,4]. Additional wavelength dependent gain measurements are used to cross check the validity of the measurements.

It has been shown, that cryogenic cooling of Yb3+-doped media is increasing laser performance significantly[1,2]. The reason for this is the thermal depopulation of the lower laser levels turning the quasi three level extraction scheme into a real four level scheme. By now most of these cryogenic cooled amplifiers aim on liquid nitrogen temperature. For future systems it has to be estimated what is an optimum operation temperature as compromise between laser performance and effort for cooling. This is needed as well from an energetic point of view as from an financial point of view. For this it is necessary to know the basic absorption and emission cross sections in dependence of temperature. We present measurement of such cross sections in an temperature range from 100K to room temperature for various gain material such as Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The absorption cross sections are calculated from the absorption spectra. The emission cross sections are determined from the absorption and emission spectra employing the Füchtbauer-Ladenburgmethod and theMcCumber relation [3,4]. Additional wavelength dependent gain measurements are used to cross check the validity of the measurements.