Search of optimized trivalent ytterbium doped-inorganic crystals for laser applications

The development of reliable InGaAs laser diode pump sources emitting in the 900-980-nm spectral range is strongly influencing the field of lasers based on Yb3+-doped solid state crystals. Ca-5(PO4)(3)F (C-FAP) and S-FAP (Sr-5(PO4)(3)F) have been recognized as favorable hosts for Yb3+ lasing in the nanosecond pulse regime. This fact has been supported by an evaluation of the spectroscopic properties of several Yb3+-doped crystals useful for laser action [1]. This evaluation was based on two parameters known from spectroscopy, the emission cross-section at the laser wavelength and the minimum pump intensity required to achieve transparency at the laser wavelength. We think that there is a need for a new evaluation of Yb3+-doped crystals in order to predict the laser efficiency in a more realistic manner in different kinds of regimes. According to a new evaluation [2-4], we present here the main spectroscopic properties of two Yb3+-doped laser crystals which are grown in our group: (i) KGd(WO4)(2) double tungstates by the nucleated floating crystal method [5] and (ii) Sc2O3 sesquioxides by the laser heated pedestal growth method [6]. The new evaluation, based on a quasi-three level laser model, leads to comparison of all known Yb3+-doped crystals in a two-dimensional diagram considering the laser extracted power in the oscillator regime and the small-signal gain in the amplifier regime. (C) 2002 Published by Elsevier Science B.V.