| Abstract [eng] |
This work investigates Ta₂O₅/SiO₂ oxide optical coatings deposited by ion beam sputtering for the 355 nm ultraviolet spectral range. Nine single-layer coatings were produced by changing the target position, oxygen flow, and Ta₂O₅/SiO₂ fraction. Reflectance and transmittance spectra were used to determine the refractive index and extinction coefficient. Increasing the SiO₂ fraction reduced the refractive index at 355 nm from about 2.30 to 1.56, while LID measurements showed that absorption decreased from about 1530 ppm for pure Ta₂O₅ to about 180 ppm for coatings with a higher SiO₂ fraction. In the B6 - B9 sample group, annealing at 300 °C reduced absorption to about 210 - 240 ppm. Based on the single-layer results, a Ta₂O₅/SiO₂ Bragg mirror was deposited. After annealing at 300 °C, its absorption decreased from 450 ppm to 232 ppm, but the laser-induced damage threshold decreased from 5.71 J/cm² to 4.48 J/cm². The results show that lower average absorption does not necessarily lead to higher laser resistance, since local defects, layer interfaces, surface morphology, and the electric field distribution inside the coating also affect the damage threshold. |
