Abstract

The Yb-Ho system is well known for its multiple possibilities of laser transitions from the visible to the middle infrared spectral region. The ytterbium codoping offers the possibility to use laser diodes at 970 nm as efficient pump sources. The energy is absorbed by Yb³⁺ and then transfered to the ⁵I₆-level in Ho³⁺, which is the upper laser level. The bleaching of the ³I₈ ground state which is the lower laser level is realized by the following processes: First of all, via the energy transfer from ytterbium. Furthermore, the ⁵I₇-level with its long lifetime of 10 ms is used as a reservoir. From this level efficient upconversion and excited state absorption processes to higher lying levels take place which not only feed population to the upper laser level but moreover prevent Ho³⁺-ions from relaxing to the ground state (Fig. 1).

© 1998 IEEE