Heat and Mass Transfer in Pulsed-Laser-Induced Phase Transformations

In terms of heat transfer, the fundamental question raised in this chapter is whether essential features of pulsed laser melting and resolidification at the nanosecond time scale can be described using a thermal model. Of specific interest is the description of the transient melting front propagation as a function of the induced temperature field. Several techniques have been developed to probe the transient temperature field during pulsed laser processing. However, as will become apparent, every technique has inherent limitations suitable only for particular materials, temperature ranges, spatial constraints, and so forth. A standard time-offlight measurement was used to measure the lattice temperature of bulk crystalline silicon during pulsed ruby laser heating [96]. This method involves measurement of the kinetic energy of particles released from the surface of the material. A characteristic temperature is extracted by fitting equilibrium Maxwellian distributions to the translational kinetic-energy data. However, the derivation of the temperature is based on the assumption that the ejected particles are in a thermal equilibrium state. Such an assumption may not be valid, particularly when the sputtering mechanism