Analysis of Tungstates and Sesquioxides, Two of the Best Yb 3+ -Doped Laser Crystals According to Different Evaluations.
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ANALYSIS OF TUNGSTATES AND SESQUIOXIDES, TWO OF THE BEST Yb3+-DOPED LASER CRYSTALS ACCORDING TO DIFFERENT EVALUATIONS. Georges Boulon, Alain Brenier, Laetitia Laversenne, Yannick Guyot, Christelle Goutaudier, Marie-Thérèse Cohen-Adad, Gérard Métrat, Noelle Muhlstein, Physical Chemistry of Luminescent Materials, Claude Bernard/Lyon1 University, UMR 5620 CNRS, Bât. A.Kastler,10 rue Ampère, Domaine Scientifique de la Doua, 69622 Villeurbanne, France. ABSTRACT The development of reliable InGaAs laser diode pump sources emitting in the 900-980 nm spectral range is stongly influencing the field of lasers based on Yb3+-doped solid state crystals. Ca5(PO4)3F (C-FAP) and S-FAP (Sr5(PO4)3F) were soon recognized to be favourable hosts for Yb3+ lasing in the nanosecond pulse regime. This fact was supported by an evaluation of the spectroscopic properties of several Yb3+-doped crystals useful for laser action. This evaluation is 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 there is a need of a new evaluation of Yb3+doped crystals in order to predict the laser efficiency in a more realistic manner in different kinds of regimes. We present here the main spectroscopic properties of two Yb3+-doped laser crystals which are grown in our Group: (i) KY(WO4)2 double tungstates by the Floating Crystal method and (ii) Y2O3 sesquioxides by the Laser Heated Pedestal Growth method. The approach, based on a quasi-three level laser model, leads to compare all known Yb3+-doped crystals in a two-dimensional diagram considering the laser extracted power and the slope efficiency. We shall show that tungstates and sesquioxides belong to the highest laser crystal potential in CW-end pumping configuration. INTRODUCTION The most promising ion that can be used in a non-Nd laser in the same range of emission wavelength is Yb3+. The Yb3+ ion have some advantages over the Nd3+ ion as laser emitting center due to its very simple energy level scheme, constituted of only two levels : the 2F7/2 ground state and the 2F5/2 exited state. There is no excited state absorption reducing the effective laser cross-section, no up-conversion, no concentration quenching. The intense Yb3+absorption lines are well suited for laser diode pumping near 980 nm and the small Stokes shift between absorption and emission reduces the thermal loading of the material during laser operation. The disadvantage of Yb3+ is that the final laser level of the quasi threelevel system is thermally populated, increasing the threshold. Among new directed searches for novel laser crystals,one important is the use of Yb3+ active ion in an inertial-fusion-energy diode pumped solid state laser. Ca5(PO4)3F (C-FAP) and Y3Al5O12 (YAG) were soon recognized to be favorable hosts for Yb lasing in the nanosecond pulse regime. This fact was supported by an evaluation of the spectroscopic properties of several Yb-doped crystals useful for laser action [1]. Th
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