Optical self-regulation during laser-induced oxidation of copper

Abstract

The oxidation of copper induced by a cw Ar+ laser beam is investigated using time-resolved reflectance measurements at λ=632.8 and 514.5 nm, together with supporting studies of film properties by scanning Auger and electron microscopies. The optical measurements and film composition analyses indicate that the oxide layer is mainly Cu2O. Since this material is partially transparent to both the probe and oxidizing laser beams, interference of each beam within the film results. This gives rise to strong reflectance variations which can be used to gain information about the oxidation reaction via theoretical simulations of the process. A model which explicitly treats the intimate relationship between temperature, oxide growth, and optical absorption is proposed. Free of adjustable parameters, the theory uses only optical, thermal, and furnace oxidation data from the literature, and gives calculated curves in good agreement with experiment. The results of this study have important consequences for investigations of the kinetics of laser-induced reactions whenever they are driven by absorption of light by a system whose optical properties depend on the reaction, i.e., are optically self-regulating.