Highly Efficient Tm³+:LiYF₄ Cascade Laser for Telecom Wavelengths

Lasers operating at telecommunication wavelengths around 1.5 μm are demanded, i.e., for optical communication, eye-safe light detection and ranging, materials processing and non-linear frequency conversion. Er<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>+-based laser systems are well established in this regard. Trivalent thulium (Tm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>+) also has potential for laser operation around 1.5 μm utilizing the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${}^{3}\mathrm{H}_{4}\rightarrow{}^{3}\mathrm{F}_{4}$</tex> transition (Fig. 1 a) [1], [2]. However, the long lifetime of ~15 ms of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${}^{3}\mathrm{F}_{4}$</tex> lower laser level facilitates self-termination, preventing continuous-wave (cw) laser operation.