Microscopic and mesoscopic aspects of laser-induced desorption and ablation

In laser-induced desorption, bonds of isolated atoms or molecules are broken even while neighboring lattice sites remain virtually undisturbed, in a process properly described by microscopic mechanisms of photoexcitation, relaxation and highly localized lattice instabilities. In laser ablation, a substantial fraction of a monolayer is ejected by each laser pulse, and mesoscopic optical and thermoelastic properties come into play. In this paper, bond-orbital theory is shown to provide a natural connection between mesoscale response to incident laser light and microscopic potentials. In the case of laser-induced desorption, it is possible to calculate two-body potentials which describe bond-weakening as electrons are promoted from bonding to anti-bonding orbitals by photon absorption. Scaling of laser ablation thresholds with various mesoscopic parameters can also be described within the framework of the bond-orbital model.