Thermodynamics and laser material processing

In many laser applications it is the conversion of photon energy to heat that drives the process. Heat transfer theory accurately describes the effects produced, and other aspects of thermodynamics need not generally be considered explicitly. The highly nonequilibrium nature of laser materials processing operations can usually be ignored once the heat transfer problem is defined. However, “equilibrium” is a concept that is basic to thermodynamics, and so it is useful to examine this concept in the context of traditional laser materials processing applications. Some of the assumptions associated with the adoption of equilibrium solutions are discussed in this article. The roles of surface reconstruction and entropy in reaching an equilibrium state are evaluated. Surface tension effects and work done during laser processing are also investigated. It is concluded that the path to the steady state in laser materials processing involves geometrical as well as thermodynamic parameters.