Laser-assisted deposition of optical coatings

Abstract

The demand for bulk-like films in the field of optical coatings stimulates the development of novel deposition techniques. Laser beams can serve as a controlled source of heat in order to modify both the deposition process and the microstructure of thin films. HfO2 and Y2O3 are evaporated by focused irradiation with the beam of a continuous-wave CO2 laser under ultrahigh vacuum conditions. Compared with conventional deposition methods the laser is an extremely clean evaporation source. Also the electron beam deposition process is modified by laser irradiation of the substrate during deposition. The refractive index, surface morphology, film structure, absorption and laser damage threshold are studied on HfO2 and Y2O3 films.A comparison of films produced by laser-assisted techniques with similar films deposited by conventional electron beam evaporation demonstrates that the porosity and absorption are reduced and the values of refractive index and laser damage threshold are increased for coatings prepared by laser-assisted techniques.