Microstructure of thin films: correlation with laser damage threshold

Microstructure and laser damage resistance of dielectric optical thin-film coatings was determined by several experimental techniques. These are film growth and test parameters as well as thin-film characteristics, e.g. absorption, structure and reflective index. The oxide coatings (HfO 2 , Nb 2 O 5 , Ta 2 O 5 , TiO 2 , and ZrO 2 ) were prepared with varying technology parameters by reactive e-beam evaporation in Leybold A1100 batch coater. The structure of the films was found to be amorphous for very thin films with tendency to columnar growth for thicker films. X-ray diffraction (XRD) and reflectivity (GIXR) were used to determine the structural properties of the films. The surface morphology of oxide layers was determined using atomic force microscopy (AFM). The optical properties were investigated in UV-IR ranges by spectrophotometer measurements. The changes in the shape of absorption edge are found to be related to the structure of thin films. Laser damage threshold for the coatings was measured at wavelength of pulsed Nd:YAG laser. Correlation between the observed film properties and laser damage threshold is discussed.