It has been recently demonstrated that it is possible to significantly alter the maximum power input required for mechanical failure of glass used for high average power laser applications by employing an ion exchange process that does not alter the optical properties of the strengthened glass. We present the analysis of the thermal stresses, fracture, and strengthening for the experimental geometry used. From this analysis the fracture strength of the untreated and treated glass can be estimated. Some suggestions for the control of thermal stresses during the operation of solid‐state lasers using glass slab geometries are presented. The second part of this report presents a micromechanical analysis of the strengthening effect due to the ion exchange process in which the enhancement in fracture strength is correlated to the depth of the zone in which ion exchange has occurred, to the length of microscopic flaws present on the surface of the glass, and to the magnitude of the microscopic volume expansion due to the ion exchange process. In particular, we consider the cases where the depth of the treated zone is much smaller or much greater than the depth of surface flaws. The magnitude of the enhancement in fracture strength is calculated in terms of these microscopic quantities for some material properties typical of phosphate glasses.