Temperature dependences of optical properties, chemical composition, structure, and laser damage in Ta₂O₅ films

Ta₂O₅ films are prepared by e-beam evaporation with varied deposition temperatures, annealing temperatures, and annealing time. The effects of temperature on the optical properties, chemical composition, structure, and laser-induced damage threshold (LIDT) are systematically investigated. The results show that the increase of deposition temperature decreases the film transmittance slightly, yet annealing below 923 K is beneficial for the transmittance. The XRD analysis reveals that the film is in the amorphous phase when annealed below 873 K and in the hexagonal phase when annealed at 1073 K. While an interesting near-crystalline phase is found when annealed at 923 K. The LIDT increases with the deposition temperature increasing, whereas it increases firstly and then decreases as the annealing temperature increases. In addition, the increase of annealing time from 4 h to 12 h is favorable to improving the LIDT, which is mainly due the improvement of the O/Ta ratio. The highest LIDT film is obtained when annealed at 923 K, owing to the lowest density of defect.