Abstract
Normal cw operation of the Tm 3H4 →3F4 transition in laser host materials is either difficult or impossible due in large part to the longer lifetime of the lower laser level compared to the upper laser level resulting in self-termination. This transition has been lased cw by codoping LiYF4 with thulium and holmium to depopulate the long-lived 3F4 Tm3− lower laser level via transfer to the Ho3+ ion while at the same time lasing the 5I7 →5I8 transition.1 The difficulty with bulk single crystal hosts, however, is that to avoid self-quenching of the 3H4 upper laser level (due to the well-known cross-relaxation process) one must stay well under Tm concentrations of 4%. This, however, restricts the effective absorption of the pump source since the crystal length is limited by practical considerations and ground-state reabsorption losses, A glass fiber host on the other hand can be doped with very small Tm concentrations, avoiding the above problems, and still obtain excellent pump absorption since the length can be easily adjusted.
© 1992 Optical Society of America
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