Laser Short Pulse Heating of an Aluminium Film: Thermal Analysis Incorporating the Equation for Phonon Radiative Transport

Laser short pulse heating of Al thin film is considered and the equation for phonon transport is introduced to formulate phonon intensity distribution inside the film. Since thermal separation of electron and lattice subsystems takes place during short pulse heating, energy transfer from the electron subsystem towards the lattice subsystem is formulated through the electron-phonon coupling parameter. Equivalent equilibrium temperature is introduced to quantify the phonon intensity distribution inside the film. It is found that electron excess energy gain from the irradiated field is high in the early heating period, which results in rapid rise of electron temperature. Because of electron-phonon collisions, the rise of equivalent equilibrium temperature in the lattice site becomes gradual in the early heating period. As the heating period progresses, equivalent equilibrium temperature increases rapidly and as electron excess energy gain reduces, equivalent equilibrium temperature becomes gradual in the lattice subsystem.