Crystal Growth And Spectra Properties Of The Doped Yb³⁺:Ca₃Ga₂Ge₃O₁₂ Crystal

With the improvement of the laser diode performance,the solide-state laser devices have been greatly developed.Especially the development of the InGaAs laser diode with a wavelength between 900 and 1,100 nm has stimulated interest in the Yb³⁺-doped laser crystals.Among the numerous of Yb³⁺-doped materials,Yb:Ca₃Ga₂Ge₃O₁2 cryatal possesses many attractive laser characteristics including broad absorption and emission band,long fluorescence lifetime,excellent optical,thermal and mechnical properties.It may be a promising laser material for high efficiency,high power diode-pumped solide-state lasers.In this paper,the growth,physical properties,thermodynamic properties,spectral and laser properties of the Yb:CGGG crystal were studied.In this paper,high-quality Yb:CGGG crystals with 5 at%and 11.5at%doped Yb concentrations were successfully grown with intermediate frequency induction heating Czochralski method.The influence of growth conditions,interracial morphology and protection atmosphere on the crystal defect occurrence was reported.In the same time, the volatile in different growth atmosphere was also studied,and the appropriate growth atmosphere(N₂ and CO₂ were 1:1 mixed) was comfirmed.Because the volatile was very serious(the main volatile was GeO₂),so the GeO₂ should be appropriate excessive in the raw materials.The main elements and their contents were determined with X-ray fluorescence method in different part of the crystal and the volatile,and their segregation coefficient especially Yb³⁺ were accounted.Using chemical corrosion method,we analysed the distribution of the dislocation, and studied the inclusion and bubbles and their formation mechanism in the crystal by the Polarizing Microscope.With the buoyancy method,we tested the practical density of the crystal,which is similar to the theoretical density.The Knoop micro-hardness of the crystal is 1257.9kg·mm^-2.The thermal properties of the crystals,including specific heat under constant pressure,thermal expansion ratio,and thermal diffusion coefficient, wree measured and the specific heat with constant volume,thermal expansion coefficient,density as a function of temperature,and thermal conductivity of the crystal were calculated using the relationship of the thermal properties.Although the attained datas are a little smaller in compared with these of YAG crystal,they are approximate,so this crystal is also a good laser crystal.The laser damage threshold of the crystal was a little smaller than that of YAG.The absorption spectra of the doped crystals and the transmittance spectra of the matrix crystals in the UV-Vis-IR aera were measured,There was not obvious absorption peak in UV-Vis aera,the reason was that CO₂ in the protection atmosphere would decompose into O₂ in high temperature situation and generates appropriate partial pressure of oxygen,which restrains the occurance of the oxygen vacancy.In the near infrared aera, there are three absorption peaks(912nm,941nm and 967nm),and the main absorption peak is at 941nm,which is almost consistent with the radiation wavelength of the InGaAs laser diode(940nm).The transmittance spectra of the matrix crystals were measured and compared to the doped crystals the results indicate that dopant has no apparent affect on the absorption of the radiative center.The transmittivity is more than 80%in the area of the doped crystals.The emission peak of the fluorescene spectrum is nearly at 1031nm,which would be red-shifted in high Yb³⁺ concentration cryatal with dopant levels of up to 11.5at%.The fluorescence lifetime of Yb:CGGG crystal is about 1.38ms.the primary laser properties of Yb:CGGG crystal were studied and it is expected that the output power would be remarkably increased if the crystal was coated.