ABSTRACT
The splitting of the electronic levels under the action of the crystal field enables laser action with a quasi-three-level scheme. Consequently, the spectroscopic characteristics and laser properties of ytterbium are particularly host-dependent. The performance of ytterbium lasers is therefore not fundamentally limited by the quasi-three-level nature of the laser scheme but more classically by thermal issues. Indeed, the fraction of absorbed power deposited as heat generates a temperature gradient inside the crystal, which in turn causes the crystal to be under stress, and ultimately could lead to fracture. This property leads to locally variable crystal field around the dopant ions and the linewidths of the electronic transitions for the ytterbium cations are found to be broader in these so called “disordered” crystals than in “ordered” laser hosts.
