[en] Growth aspects of barium strontium titanate, Ba_0.6Sr_0.4TiO₃ (BST) thin films grown on Si (100) and quartz substrates by pulsed laser deposition technique were investigated. The main objective of the work was to study the effect of substrate temperature and oxygen partial pressure on the microstructure and optical properties of the BST films. X-ray diffraction results revealed that the thin films were amorphous when the substrate temperature was up to 673 K and the crystallinity was found to be improved at the substrate temperature of 873 K. There was an increase in the lattice parameter value from 3.97 to 4.01 Å with an increase in the oxygen partial pressure. Scanning electron microscopy revealed smooth and uniform surfaces, while atomic force microscopy revealed that the particle size increased with decreasing oxygen partial pressure. UV-visible spectroscopy showed that the band gap of the BST films deposited on quartz substrate decreased from 4.41 to 3.73 eV as deposition temperature increased from 303 K to 873 K. (paper)