Growth And Characterization Of RE:(Lu_xGd_1-x)₃Ga₅O₁₂(RE=Er³⁺,Dy³⁺) Mid-Infrared Laser Crystal

Nowadays,2～3 μm Mid-Infrared(MIR)laser has attracting much attentions in the fields of biomedical,spectral detection,and space military.Mid-infrared laser,also known as "eye-safe" laser,is located in the "molecular fingerprint" spectral region and has the characteristics of low photon energy.In addition,middle infrared laser is also the ideal pumping source of middle and infrared laser optical parametric oscillator.At present,one of the main output ways of mid-infrared laser is rare earth doped crystal laser.However,due to the drawbacks of matrix crystal on phonon energy thermal properties,the output power and efficiency of laser in this band still need to be improved.Therefore,developing high-qualitative 2～3 μm infrared laser is of great significance.The main purpose of this thesis is to prepare high-efficiency mid-infrared laser crystals by exploring growth technology,regulating crystal doping ratio and optimizing laser experiments.On the one hand,starting from the optimization of crystal structure,rare earth Lu3+ions are introduced on the basis of Er:GGG crystal to match the size of Er3+ ions,so as to balance the ion spacing and increase the disorder of crystal structure.On the other hand,starting with the doping of new rare earth ions,Dy3+ ons which can prodice a wide emission spectrum are introduced on the basis of LGGG crystals,in the end high quality Dy:LGGG crystals with good thermal properties were successfully grown.This paper is mainly composed of three parts,the specific content is as follows:1.Growth and characterization of Er:LGGG(Er:5%,Lu:10%)crystals.5%Er:LGGG crystal with the dimensions of Φ36 × 45 mm3 was grown by Czochralski method for the first time.The crystal was tested by Laue,XRD and XRF.The separation coefficient of Er3+ ion is 0.97.The density of the measured crystal is 7.15 ± 0.02 g/cm3 and the change of density with temperature is calculated.The thermal expansion,specific heat,thermal diffusion and thermal conductivity of the crystals with temperature were studied.It is found that the maximum half-peak width of the crystal at 967 nm is 11 nm,larger than that of Er:GGG crystal,which is very favorable for LD pumping.Finally,the fluorescence spectra and fluorescence lifetime of the crystal were tested,and the fluorescence lifetime of the upper level was 0.584 ms.2.Growth and characterization of Er:LGGG(Er:20%,Lu:10%)crystals.The doping ratio of Er3+ ion was optimized,high doping of 20%Er:LGGG crystal with the size of Φ 16 × 48 mm3 was grown by the Czochralski method.The separation coefficient of Er3+ ion was calculated as 1.04.The upper level fluorescence lifetime of the crystal is 1.42 ms,which is longer than that of Er:GGG crystal.The lower level fluorescence lifetime is 5.18 ms,less than Er:GGG crystal,which is very favorable for laser output.The transition probability,fluorescence branching ratio and radiation lifetime were analyzed by Judd-Ofelt(J-O)theory,and the fluorescence emission cross section was calculated.With a 976 nm laser diode as the pump source and an output coupling mirror transmittance of 3%,a maximum skew efficiency of 8.5%and a power of 350 mW can be achieved.The laser emission wavelength of 20%Er:LGGG is 2818 nm and the half-peak width is 17.49 nm,and the output power stability(RMS)is 1.5%at 350 mW for 2 hours.The beam quality is tested,and the horizontal and vertical directions are 1.374 and 1.228,respectively.Its comprehensive performance is better than that of Er:GGG crystal,indicating that Er:LGGG crystal has great potential in 3μm band.3.Growth and characterization of Dy:LGGG(Dy:2%,Lu:20%)crystals.Dy:LGGG crystal with the size of Φ 32 × 20 mm3 was grown by Czochralski method.The XRF test shows that the separation coefficient of Dy3+ ion and Lu3+ion in Dy:LGGG crystal is 0.4 and 0.583,respectively.The thermal expansion,specific heat and thermal diffusion and the change of thermal conductivity with temperature have been tested.It has been calculated that the crystal mean linear thermal expansion coefficient is 9.8 × 10-6 K-1,which is higher than the GGG crystal.