Growth And Mechanism Of Yttrium - Doped Yttrium Vanadate And Yttrium Phosphate Series Laser Crystals

As the development of laser diodes, the diode pumped solid state lasers have played the important role in many fields, such as the scientific research, military,medicine, material processing and our daily life, because of its high efficiency, high integration and high stability. The laser gain medium is the core element for the laser technology. A perfect laser gain medium will promote the laser technology developing rapidly. As the most important part of the laser gain medium, laser crystal with high quality and big size often play as the milestone of laser development, such as the Nd:YAG crystal and Nd:YVO₄ crystal. In order to obtain crystals with high quality and big size, it is necessary to optimizing the growth processes through understanding the crystal structure and characterizing and analyzing the defects of crystal.The Yb doped vanadate crystals have been proved as good laser crystals with excellent laser performance in continuous wave and plus mode, and also show some interesting laser performance such as the bistable of output laser and the transformation of laser polarized states. Researching on this series of laser crystals will contribute to obtain more excellent laser output and guide the new laser crystal exploration in some extent. Up to mow, the laser performances of the Yb:YVO₄,Yb:LuVO₄, Yb:GdVO₄, Yb:Y_xGd_1-xVO₄ and Yb:LuxGd_1-xVO₄ in vanadate series crystals have been studied, the Yb:Y_xLu_1-xVO₄ crystals have remainly not been grown.So the czochralski method was used to grow the Yb:Y_xLu_1-xVO₄ laser crystals, and the properties were characterized. The orthophosphate crystals possess the structure with the vanadate crystals and own good physical chemistry properties. The preliminary laser results of the Yb doped orthophosphate crystals shows that the Yb doped orthophosphate crystals will be excellent laser gain medium. The orthophosphate crystals were difficult to grow. A breakthrough in crystal growth was necessary for the property characterizations,such as laser property, thermal property and so on.The contents of this dissertation are outlined as following:The Yb:Y_xLu_1-xVO₄ series crystals were grown by Czochralski method successfully for the first time. The crystal growth equipment, crystal growth method and technological processes were introduced. The crystal shape morphology was discussed combining with the crystal thermodynamic theory. The influences of temperature on the crystal shape morphology during different growth stage were also discussed. The influence factors on crystal quality were discussed in the terms of thermodynamic and kinetic, such as material purity, temperature field, crystal seed,anneal procedure and so on.The（100） face and（001） face were etched by different corrosives with proper time. The density and distribution of dislocations in crystal were characterized by etch pits. The TEM diffraction contrast image was used to characterize the dislocation morphology in the（100） face. Both the results show that the density of dislocations in the（001） face was bigger than the（100） face’s, which was explained with the crystal structure. The structure of edge dislocation was observed by using the HRTEM image directly, the two dislocations with equal and oppo-site burgers vector were found. The thermal expansion coefficient of the crystal was tested. By analyzing the crystal structure and the thermal expansion coefficient, the possible reason for the pair of dislocations were given: during the anneal procedure after crystal growth, the thermal stress caused by the anisotropy of thermal expansion make the（010） face break up into two half atomic face and forming two edge dislocations.The Yb:YPO₄ crystal was grown by spontaneous nucleation method using Pb2P2O7 as flux. The influences of the proportional change of PbO and P2O5 on crystal growth was tested and discussed. In order to improve the mater transport of the crystal growth system, the alkali metal ion was used to reduce the viscosity of the solution. As a result, the crystal size became bigger and the amount of the nucleation reduced. The XRD was used to determined the crystal structure, which showed that the additives did not change the Yb:YPO₄ structure and confirmed the effectiveness of the flux system improvement. The polarized absorption spectra were measured, and the absorption cross-sections and linewidth were calculated. The continuous wave（cw）laser operation of Yb:YPO₄ crystal was obtained successfully in the room temperature.The laser output power was 0.36 W when the absorbed pump power reached 2.2 W.The laser emission spectra for the different output couplings were measured.