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

Tantalum pentaoxide (Ta 2 O 5 ) 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 Ta 2 O 5 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 Ta 2 O 5 film was demonstrated to be homogeneous in refractive index and amorphous in microstructure. The absorption and stress of Ta 2 O 5 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 Ta 2 O 5 film with negligible water adsorption. Finally, a 1064 nm Ta 2 O 5 /SiO 2 high-reflectance (HR) coating was prepared, and the influence of the Ar/O 2 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.