Fracture Limit

The mechanical properties of the laser host material determine the maximum surface stress that can be tolerated prior to fracture. If there were no other constraints, such as stress-induced focusing and birefringence, the thermal loading and thus average output power of a rod laser could be increased until stress fracture occurred. If σ_max is the maximum surface stress at which fracture occurs,

..........(1)

then we can rewrite (1) as follows:

..........(2)

where

........(3)

is a “thermal shock parameter.” A larger R_s indicates a higher permissible thermal loading before fracture occurs. Table 1.1 lists typical values for a number of laser materials if we assume a standard surface treatment.

TABLE 1.1. Thermal shock parameter for different materials.