Growth Of Cr,Ca:GGG Single Crystal And Influence Of Annealingand Radiation On Cr Recharging Process

Cr⁴⁺ doped crystals are widely used in tunable and passive Q-switched lasers.Tunable lasers are widely used in medical science,measurement,detection,communication and photoelectric confrontation.As the premise and basis of all solid state laser,tunable laser crystal plays a vital role in the new all solid tunable laser;The passive Q-switch laser is widely used in narrow pulse width,high peak power laser pulse;the application covers industry,medical military and so on.Cr⁴⁺ doped crystals have wide emission bandwidth and match with some pump laser wavelengths and accessible to get compact ultrashort pulse output.As saturable absorbers,Cr⁴⁺ doped crystals are the most extensively used Q-switched for the 1 μm band.The study of Cr⁴⁺ doped crystal laser materials and devices have become one of the hottest field in laser materials.In this paper,Cr,Ca:GGG polycrystals were synthesized by solid-phase synthesis method under the temperature of 1200℃.GGG crystals co-doped with Ca2+ and Cr⁴⁺（Cr,Ca:GGG）were successfully grown in an atmosphere（98%Ar + 2%O2）by Czochralski method.The content of each element in the crystal were analyzed by X-ray fluorescence spectroscopy（XRF）.The optical homogeneity and the rocking curve of the as-grown crystal was tested,the optical uniformity of the crystal was good and the lattice was intact.The defects in the crystals were explored by means of chemical etching using polarization microscopy.The thermal properties of the crystals were tested,including thermal expansion,thermal conductivity and thermal diffusion.The influence of annealing conditions on Cr recharging process,from Cr3+ to Cr⁴⁺was investigated by an absorption spectrometry.The optimum annealing condition was determined after taking into consideration various factors,including annealing temperature,time of duration,and the concentration of O2 in annealing atmosphere.The annealed Cr,Ca:GGG crystal slab was used as a saturable absorber in Q-switched lasers successfully.For the Q-switching operation,the maximum output power of 2.26 W was obtained with 40%output mirror.The shortest pulse width of 10.19 ns was obtained with 4.2%output mirror under the absorber pump power of 2.19 W.