Assessment of the Thermal Shock Resistance of Neodymium Doped Alumino-Phosphate Laser Glasses

Abstract

The resistance to thermal shock is one of the main properties to be considered in the design of glasses for their application as high power and high energy laser glasses. Neodymium doped phosphate glasses have inherent spectroscopic advantages for their use as laser hosts, however, their rather low mechanical performance can be a limiting factor for their use. It is very important to characterise the thermo-mechanical resistance of proprietary phosphate glass compositions as laser glasses, however, it is not common to find systematic studies on the influence of glass composition on the thermal shock resistance in phosphate glasses, which is defined as the mechanical resistance of the material to the stresses generated by thermal fluctuations. This includes considering the elastic properties of the medium, its thermal conductivity, the coefficient of thermal expansion and the fracture toughness. In the present work we have studied these properties in a series of alumino-phosphate glasses doped with Nd₂O₃ as a function of the alumina content. The above properties have been determined by Brillouin spectroscopy, dilatometry and thermal diffusivity, while the fracture toughness has been approached by means of a theoretical model that uses the calculation of the energy necessary to create a new surface while a pre-existing crack progresses. The results showed that the calculated fracture toughness agrees with the one of similar commercial laser glass compositions, and that the thermal shock resistance calculated in the metaphosphate glasses increases with the addition of Al₂O₃.