High-performance Ta2O5 films prepared by plasma ion-assisted deposition for low-absorption optics

Abstract

Tantalum pentaoxide (Ta2O5) films prepared by plasma ion-assisted deposition (PIAD) with different bias voltages of advanced plasma source were investigated in detail. The optical and micro-structural properties of single-layer Ta2O5 films were characterized by UV-VIS and FTIR spectrophotometers, laser calorimeter (LCA), optical interferometer, atomic force microscope (AFM), and x-ray diffraction (XRD), respectively. The dependences of optical and micro-structural characteristics of thin film on the bias voltage were analyzed. The prepared Ta2O5 film was demonstrated to be homogeneous in refractive index and amorphous in microstructure. The absorption and stress of Ta2O5 film were mainly dependent on the bias voltage, while the root-mean-square roughness decreased with the increasing bias voltage. Furthermore, it was found that a bias voltage greater than 120 V was necessary to fabricate dense Ta2O5 film with negligible water adsorption. Finally, a 1064 nm Ta2O5/SiO2 high-reflectance (HR) coating was prepared, and the influence of the Ar/O2 plasma treatment time on the absorption and reflectivity of multilayer film was researched. The experimental results showed that a low absorption loss (4.4 ppm) for the 1064 nm HR coating could be achieved by the PIAD process with the plasma treatment.