Abstract: A thin film deposition process for depositing a metal oxide layer onto a substrate body, the process comprising the steps of taking a metal organic compound in vapor form, the compound being capable of absorbing light in the wavelength range of 240 to 400 nanometers, heating the substrate to a temperature below the pyrolytic decomposition temperature of the compound in the presence of the vapor, directing light towards the substrate to cause a photochemical fragmentation of said vapor molecules, the reaction resulting in a deposition of the required oxide on said substrate.The metal organic compound may be a metal alkoxy substituted beta-diketonate such as aluminium diisopropoxide acetyl acetonate.