Study On Luminescence From ¹D₂ Level Of Pr:YLF Crystal

Near-infrared（NIR）lasers have been widely applied in many fields such as industrial processing,biomedicine,optical communication.Particularly,rare-earthdoped solid-state lasers have gotten a wide range of attention and research for many advantages such as smaller volume,lighter weight and higher efficiency.So far,the rare-earth ions commonly applied for generating NIR lasers are Nd³⁺,Yb³⁺,Er³⁺,Tm³⁺and Ho³⁺ respectively.However,except for these rare-earth ions,the ion of Pr³⁺,which is well-known for being widely applied for visible lasers,can also contribute to the studying of NIR lasers because the ¹D₂ level has extremely rich NIR transitions.Nevertheless,the 3PJ level with abundant visible transitions has attracted people’s excessive attention for a long time,while the ¹D₂ level with great potential in NIR lasing have been ignored all the time.For further studying luminescence properties of ¹D₂ level deeply,the Pr:YLF crystal was selected as a research object for its mature growth and excellent performance,then the polarized spectra of YLF crystals with different Pr³⁺ concentrations were measured.Meanwhile,the spectral analyses were conducted detailly,including J-O analysis and theoretical analysis of lasing characteristics,all these could bring a comprehensive study on the luminescence characteristics of ¹D₂ level theoretically.The main contents can be summarized as follows:（1）The absorption and emission spectra of different Pr:YLF crystals were measured,and detailed J-O theoretical analyses have been conducted.Firstly,four YLF crystals with Pr³⁺ concentrations of 0.3 at.%,0.5 at.%,1.0 at.%,2.0 at.%were treated as experimental samples,for getting the polarized absorption spectra and emission spectra respectively.Next,according to the measured absorption spectra,the standard and modified J-O models were applied for calculating J-O parameters respectively,the optimal model for spectral analyses in this work could be ensured by a comparative study.Then the ¹D₂ emission characteristic parameters such as emission cross sections and quantum efficiency were studied deeply,which were based on the calculation of optimal model,measured polarized emission spectra and fluorescence decay curves.Finally,all the peak wavelengths of each transition originated from ¹D₂ level were picked out for further calculating parameters such as optical gain factors and saturation intensity.In addition,the relative threshold of different Pr:YLF crystals were compared,and the 2.0 at.%sample could be determined as the most suitable Pr:YLF crystal for further studying laser.（2）The laser characteristics of ¹D₂ level have been theoretically predicted.Detailly,the 2.0 at.%Pr:YLF crystal was treated as a research object,and the peak wavelengths with larger emission cross sections at ¹D₂→¹G₄,3F³⁺³F₄,³H₆+³F₂,³H₅ transition were selected as lasing wavelengths to be investigated,then the laser characteristic parameters including threshold and slope efficiency were calculated.Additionally,the effects on these parameters from pump spot radius and output mirror’s transmittance were investigated.