Growth And Spectroscopic Characterization Of Infrared Laser Crystals In SrLaAlO₄ Activated By Rare Earth Ions

The emission range of 2.7-3μm mid-infrared laser overlaps with the strongest absorption band of water vapor in the atmosphere,which can reduce transmission losses,and has been widely used in medical surgery,optoelectronic countermeasures,environmental monitoring,and remote sensing.In recent years,due to the rapid development of high-power laser diodes（LDs）,using LD direct pumping for rare earth ion-doped laser crystals has become an important means to obtain 2.7-3μm mid-infrared lasers.Among many rare earth ions,the transition radiation wavelengths of Er³⁺:⁴I_11/2→⁴I_13/2 and Ho³⁺:⁵I₆→⁵I₇ are exactly in the 2.7-3μm wavelength range.In this paper,we chose Sr La Al O₄ as the substrate crystal,and carried out the growth and spectral study of Er³⁺and Ho³⁺-doped Sr La Al O₄ mid-infrared laser crystals.The specific research contents are as follows:（1）Using the Czochralski method,we grew 10at%Er³⁺single-doped Sr La Al O₄ crystals,and measured their room temperature polarized absorption spectrum,fluorescence emission spectrum,and fluorescence decay curve.Based on the Judd-Offelt（J-O）theory,a series of important spectral parameters were calculated.Theσandπpolarized absorption cross-sections at 978 nm were 2.4×10^-21 cm² and 1.4×10^-21 cm²,respectively.In addition,the maximum emission cross-section appeared at 2745 nm,which was 0.71×10^-20 cm².The energy level lifetimes of the upper level ⁴I_11/2 and the lower level ⁴I_13/2 were 1.06 ms and 4.42ms,respectively,indicating that there was a self-termination effect in the 2.7μm transition of Er³⁺:Sr La Al O₄ crystal.（2）In view of the self-termination effect of 10 at%Er³⁺:Sr La Al O₄ crystal,this paper used the method of co-doping with activated ions Pr³⁺and Sm³⁺to optimize it.We grew10at%Er³⁺/0.5at%Pr³⁺:Sr La Al O₄ and 10at%Er³⁺/0.5at%Sm³⁺:Sr La Al O₄ crystals by the Czochralski method,and conducted spectral studies under the same testing conditions as the single-doped crystals.The results showed that after co-doping with Pr³⁺,not only the upconversion and near-infrared luminescence were weakened,but also the emission in mid-infrared was enhanced.The fluorescence lifetime of the lower level ⁴I_13/2 was reduced from4.42 ms to 0.93 ms,which greatly improved the self-termination effect.After co-doping with Sm³⁺,the same phenomenon of weakened near-infrared luminescence and enhanced mid-infrared luminescence occurred.At the same time,the energy level lifetime of ⁴I_13/2 decreased from 4.42 ms to 0.98 ms,which also greatly improved the self-termination effect.The experiment showed that Er³⁺/Pr³⁺:Sr La Al O₄ crystals and Er³⁺/Sm³⁺:Sr La Al O₄ crystals both have great potential to achieve laser output in the 2.7-3μm mid-infrared range pumped by LD.（3）We grew Sr La Al O₄ crystals doped with different concentrations（1at%,2at%,3at%）of Ho³⁺,3at%Ho³⁺and sensitizing ions(10at%Yb³⁺)and co-doping ions(0.5at%Eu³⁺),and calculated a series of spectral performance parameters.The results showed that 3at%Ho³⁺:SLA crystal was the most suitable for mid-infrared laser output,but lacked peak matching with commercial high-power LDs.When Yb³⁺and Eu³⁺were co-doped,Yb³⁺made it suitable for commercial 980 nm LD pumping,and Eu³⁺not only suppressed the near-infrared luminescence,enhanced the 2.86μm luminescence,but also shortened the lifetime of the Ho³⁺:⁵I₇ level.According to the research results of this paper,Ho³⁺/Yb³⁺/Eu³⁺:Sr La Al O₄crystal is expected to be pumped directly by commercial LD to achieve 2.86μm mid-infrared laser output.