Abstract: Combining the advantages of high thermal conductivity, large emission bandwidth and appropriate emission cross-section, the fluorite-type laser crystal Nd,Y∶SrF₂ (NYSF) has important application in high-power laser techniques. Dislocation in laser crystals is an important category of microscopic defects which implies the integrity of crystalline lattice structure, and influences the mechanical and optical performances of crystals. The NYSF crystals were grown by vertical Bridgman method and the optimized experimental parameters for chemical etching of dislocation defects were obtained by comparing the influence of various etching conditions on the morphology of etch pits in in NYSF crystals. The optimized etching condition are: concentration of 4 mol/L hydrochloric acid solution as a corrosive solution and corrosion temperature of 60 ℃ and corrosion time of 9~12 min. The evolution of dislocation etch pit morphology was studied and the relationship between the lattice structure and the morphology of etch pits was analyzed. The distribution of dislocation defects in NYSF was characterized by chemical etching method. The axial distribution first decreases and then increases from the shouldering to the tail, and the radial distribution gradually increases from the center to the edge. The influence of crystal growth processes on the formation of defects was discussed and the possible reason why dislocation density increases with increasing crucible drop rate was proposed.

Key words: Nd,Y∶SrF₂, laser crystal, fluoride crystal, vertical Bridgman method, dislocation, etch pit morphology, crystal defect