The inclusion problem in laser glass

The problem of inclusion damage in laser glass is considered with attention directed to an improved treatment of the stress around a hot inclusion particle. The existence of a layer of molten glass surrounding such particles is suggested; and the new analysis indicates a maximum tensile stress in the nearby cooler glass, rather than at the solid- liquid glass boundary. The magnitude of this tensile stress can exceed the expected strength of the glass for a range of particle sizes under high power laser operation, and failure is then expected to occur. Thereakdown condition is shown to depend upon the flux level and pulse time of the laser beam, as well as the size and shape of the inclusion particles and various material properties of the inclusion and glass. Under most conditions of laser operation, nonmetallic inclusions - even those containing large concentrations of highly absorbing ions - are expected to be safe; and under all conditions they should be appreciable less dangerous than similar metal particles.