Power scaling of thin-disk Tm-lasers based on Tm:KLu(WO4)2/KLu(WO4)2 epitaxy

Monoclinic double tungstate (DT) crystals, due to their maximum absorption and emission cross sections and minimum concentration quenching, seem ideal as hosts for thin-disk lasers with simplified geometry (number of pump passes). The first diode-pumped thulium thin-disk laser based on Tm:KY(WO₄)₂ generated CW output power of 4.9 W at 1950 nm using 4 pump passes [1]. The power handling capability of the thin-disk concept scales inversely proportional to the thickness and the high absorption of the monoclinic DTs reveals another important advantage of these anisotropic materials - enormous scaling potential, which, however, could be technically exploited by only relying on doped epitaxial layers. Recently, employing Tm-doped epitaxial layers grown on un-doped KLu(WO₄)₂ (KLuW) and 4 pump passes, we achieved 47% slope efficiency and CW output power of 5.9 W [2]. Here, we study the power scaling potential of this laser in the quasi-CW (QCW) mode.