Ion-pair upconversion pumped laser emission in Er3+ ions in YAG, YLF, SrF2, and CaF2 crystals

Abstract

Ion‐pair upconversion pumped laser emission at 2.7–2.9 μm between the ⁴I_11/2 and ⁴I_13/2 excited states of triply ionized erbium ions (Er³⁺) has been studied at 300 and 100 K in YLF, YAG, SrF₂, and CaF₂ hosts. Laser action was obtained by pumping directly into the transition’s terminal laser level. In all four hosts, the lifetime of the ⁴I_13/2 state is longer than that of the ⁴I_11/2 state, by factors of 5 and 80 for the first two, and factors of (5)/(2) and 2 for the SrF₂ and CaF₂, respectively. The absorption coefficient for the 1.533‐μm pump radiation is comparable in YLF, SrF₂, and CaF₂, but is larger by a factor of 3 in YAG. At room temperature the threshold pump energy for YAG is larger by a factor of 10 than for CaF₂, SrF₂, and YLF. Interpretation of the lasing delay times at threshold pumping levels in terms of a simple analytic model gives for the upconversion coefficients: α_YLF =1.2×10⁻¹⁷ cm³ s⁻¹, α_YAG =5.4×10⁻¹⁷ cm³ s⁻¹, αSrF₂ =2.9×10⁻¹⁵ cm³ s⁻¹, and αCaF₂ =3.2×10⁻¹⁵ cm³ s⁻¹. Nonoptimized upconversion pumped laser efficiency in Er:YLF was measured at 110 K to be 17%. A peculiar upconversion pumped lasing behavior was observed in Er:YAG at low temperatures.