Cascade laser optimization for 3H4 → 3H5 and 3F4 → 3H6 sequent transitions in Tm3+-doped materials.

Abstract

We study a cascade laser scheme involving the 3H4 → 3H5 and 3F4 → 3H6 consecutive transitions in Tm3+-doped materials as a promising technique to favor laser emission at 2.3 µm. We examine the conditions in terms of the Tm3+ doping levels for which the cascade laser is beneficial or not. For this, Tm:LiYF4 lasers based on crystals with several doping levels in the range of 2.5 - 6 at.% with and without cascade laser are studied. For low doping of 2.5 at.% Tm3+, adding the laser emission at 1.9 µm allows to double the output power at 2.3 µm, whereas for high doping of 6 at.%, allowing the laser to operate at 1.9 µm totally suppresses the laser emission at 2.3 µm. An analytical model is developed and confronted with experimental results to predict this doping-dependent phenomenon and forecast the potential benefits. This study of cascade laser emission on the 3H4→ 3H5 and 3F4→ 3H6 transitions versus the Tm3+ doping level is finally extended to other well-known Tm3+-doped laser materials.