Effect of Ga3+/Sc3+ on Yb3+ emission in mixed YAG at cryogenic temperatures Jan Hosta?a1,*, Venkatesan Jambunathan2, Dariia Chernomorets1,3, Andreana Piancastelli1

Emerging applications namely high harmonic generation, laser driven inertial fusion energy, laser shock peening, soft X-ray source and other commercial applications require laser sources with high average and high peak power (HAPP). To develop such HAPP laser sources, Yb:YAG is one of the most preferred gain media operating at cryogenic temperature either as ceramic or crystalline forms. At room temperature due to quasi-three level system this Yb:YAG is thermally populated leading to very high reabsorption losses, minimizing the laser efficiency. However, at cryogenic temperatures, it behaves as a four-level system minimizing the reabsorption losses, leading to higher efficiency. In addition, at cryogenic cooling Yb:YAG shows excellent thermo-optical and spectroscopic properties, which play a major role in overall performance of the laser systems [1]. Neverthelss, the emission bandwidth of Yb:YAG decreases with decrease in temperature [2], that limits the generation of short pulses in the sub picosecond and femtosecond regime which is essential for HAPP lasers. To improve this emission broadening, one way is to introduce some imperfections in the host matrix and create structural irregularities, viz. adding other cations such as Sc3+ and Ga3+ in the YAG site. Taking into account the above said facts, this work is devoted to study the emission properties at cryogenic tempertures on the effect of different concentration of Sc3+ and Ga3+ ions in Yb:YAG. Three different sets of mixed garnets Y3(Al1-x-yScxGay)5O12 doped with 3at.%Yb were prepared using solid state sintering route. They were characterized in terms of XRD, SEM and cryogenic emission spectroscopy. From the cryogenic emission spectra (100 K) of the mixed garnets, it is evident that there is a significant emission broadening for Ga3+ and Sc3+admixed Yb:YAG samples whereas the broadening is weaker in Sc3+ admixed Yb:YAG. All the experimental details along with the obtained results will be discussed in detail. [1] D.C. Brown, S. Tornegård, J. Kolis, High Power Laser Sci. Eng. 4 (2016) e15. [2] J. Körner, V. Jambunathan, J. Hein, R. Seifert, M. Loeser, M. Siebold, U. Schramm, P. Sikocinski, A. Lucianetti, T. Mocek and M. C. Kaluza, Appl. Phys. B 116 (2014) 75.