Abstract
The spectral properties and laser performance of Er:SrF2 single crystals were investigated and compared with Er:CaF2. Er:SrF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er3+:4I11/2 level) than those of Er:CaF2 crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF2 single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF2 with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.
Highlights
In Er3+ based oxide crystals, such as Y3Al5O12 (YAG)[11,14,15], Gd3Ga5O12 (GGG)[16] and Gd3−xYxSc2Ga3O12 (GYSGG)[1,7] etc, the Er3+ doping concentrations vary from 30 at.% to as high as 50 at.%
This work we aim to investigate and compare the spectral properties and laser performance of Er:SrF2 and Er:CaF2 single crystals
We report dual-wavelength continuous-wave lasers around 2.8 μm in both 4at.% and 10at.% Er:SrF2 single crystals under 972 nm laser diode (LD) end pumping. 4at.% Er:SrF2 demonstrated the best laser performance with a low threshold of 0.100 W, a high slope efficiency of 22.0% and an maximum output power of 0.483 W
Summary
In Er3+ based oxide crystals, such as Y3Al5O12 (YAG)[11,14,15], Gd3Ga5O12 (GGG)[16] and Gd3−xYxSc2Ga3O12 (GYSGG)[1,7] etc, the Er3+ doping concentrations vary from 30 at.% to as high as 50 at.%. Compared with oxide crystals mentioned above, SrF2 crystal same as CaF2 crystal have an key advantage that is rare earth ions tend to form clusters even when the doping concentration is low[17,18]. Such clusters additional shorten the distance between Er3+ ions and enhances the energy transfer process between them, which is beneficial for achieving mid-infrared laser under low doping concentration. The fluorescence lifetimes of Er3+:4I11/2 level were measured with an Edinburgh FLS920 fluorescence spectrophotometer, using an ns OPO laser, emitting at 980 nm, as excitation source.
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