Effects Of Deposition Rates On Laser Damage Threshold Of Tio_2/sio_2 High Reflectors

摘要

TiO_2 single layers and TiO_2/SiO_2 high reflectors (HR) are prepared by electron beam evaporation at different TiO_2 deposition rates. It is found that the changes of properties of TiO_2 films with the increase of rate, such as the increase of refractive index and extinction coefficient and the decrease of physical thickness, lead to the spectrum shift and reflectivity bandwidth broadening of HR together with the increase of absorption and decrease of laser-induced damage threshold. The damages are found of different morphologies: a shallow pit to a seriously delaminated and deep crater, and the different amorphous-to-anatase-to-rutile phase transition processes detected by Raman study. The frequency shift of Raman vibration mode correlates with the strain in film. Energy dispersive X-ray analysis reveals that impurities and non-stoichiometric defects are two absorption initiations resulting to the laser-induced transformation.