Abstract: The poly-crystalline silicon films deposited on an insulating substrate by LPCVD are recrystallized by CWAr⁺ laser irradiation. According to the relations between the average crystal-grain size and the laser power, we can divide the recrystallizing process into three stages, called solid phase crystallization, liquid phase crystallization and saturated crystallization. There exists a power window restricted by the recrystallized grain size, the properties of the interface between the polysilicon and SiO₂ layer as well as the irradiation damages. In this paper we analyse the mechanism of the formation of the irradiation damage and propose to diverge the laser beam and increase the thickness of SiO₂ in order to widen the power window.