Laser evaporation studies

The use of a pulsed laser to evaporate dielectric materials for optical thin film deposition was investigated. Studies were performed to analyze the species present in the evaporant plume generated by a 1.5 Joule TEA-CO2 laser. the materials investigated were Al2O3, SiO2, ZnO, PbF2, TiO2, and HfO2. Experiments were performed in a cryopumped system with a base pressure of 10 to the 8th power torr. The evaporant plume was characterized using luminescence spectroscopy, mass spectroscopy, and ion current analysis. Luminescence studies indicated the existence of excited state neutrals and singly, doubly and triply ionized species. Plasma electron temperatures of 6500 K were deduced from a study of neutrals in the plumes of SiO2 and Al2O3. Molecular species were found in significant concentrations only for higher (.001 torr) residual gas pressures. Ion current analysis demonstrated the existence of several species for each compound, each with different velocities. Velocities of 15 million cm/sec indicated very high kinetic energies for the ionized species. In the following phase of the program, the effects of excited state and energetic species on thin film growth will be investigated.