Cascade laser optimization for <sup>3</sup>H<sub>4</sub> → <sup>3</sup>H<sub>5</sub> and <sup>3</sup>F<sub>4</sub> → <sup>3</sup>H<sub>6</sub> sequent transitions in Tm<sup>3+</sup>-doped materials
Hippolyte Dupont, Lauren Guillemot, Pavel Loiko, Rosa Maria Solé, Xavier Mateos, Magdalena Aguiló, Francesc Dı́az, Alain Braud, Patrice Camy, Patrick Georges, Frédéric Druon
Abstract
We study a cascade laser scheme involving the 3 H 4 → 3 H 5 and 3 F 4 → 3 H 6 consecutive transitions in Tm 3+ -doped materials as a promising technique to favor laser emission at 2.3 µm. We examine the conditions in terms of the Tm 3+ doping levels for which the cascade laser is beneficial or not. For this, Tm:LiYF 4 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.% Tm 3+ , 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 3 H 4 → 3 H 5 and 3 F 4 → 3 H 6 transitions versus the Tm 3+ doping level is finally extended to other well-known Tm 3+ -doped laser materials.