Kinetic control of surface patterning by laser-induced photochemical deposition in liquid solutions. I. Theoretical developments.

We theoretically analyze the real-time formation of holographic grating driven by laser-photochemical deposition in liquid solutions. Considering the one-photon excitation of a two-level system, we present a reaction/diffusion description of the species produced photochemically by the excitation of a continuous laser wave. By assuming that a deposit is heterogeneously nucleated on the substrate when concentration of the reaction product reaches solubility, we develop a thermodynamic analysis of its late-stage growth under laser irradiation. A rate equation is proposed and used to describe the kinetics of three different types of patterning: dot array, periodic line writing, and holographic grating formed by two interfering beams. In each case, the predicted deposit growth laws show the emergence of scaling regimes that give rise to a universal picture of the processes involved, whatever the initial photosensitive medium is. Due to the crucial role played by patterned coatings in numerous practical applications (lithography or holography, for instance), this control in situ of the kinetics offers the opportunity to totally monitor the desired patterning. It also suggests the way to develop a unified description for holographic grating formation driven by photochemical deposition.