Abstract: A substrate is brought into close proximity with one or more gas injectors to deposit a thin film. As the substrate is moved horizontally along a predefined direction, it is injected with reactive gases and pyrolytically heated with a heating light focused on the substrate. To prevent photolytic reactions, the heating light source is preferably on the side of the substrate opposite to the side where the reactive gases are deposited. In some embodiments, this heating light source is supplemented by heating light sources on the same side of the substrate as the deposited reactive gases. The heating light source(s) has a wavelength to optimize absorption by the substrate or the deposited film layer.