The absorption loss of a film primarily occurs owing to absorption during the deposition process, considerably influenced by process parameters such as the ion source voltage and current, oxygen flow rate, and substrate temperature. The ion source bias voltage influences the auxiliary ion energy; a low bias voltage does not have a good auxiliary effect, and a high bias voltage may introduce ion source contamination. Therefore, studying the properties of different ion source bias voltage-assisted deposition films is necessary.

Ta₂O₅ monolayer films were prepared via electron beam evaporation and an ion-assisted technique. The film samples were plated with a Syruspro1110 coater from Leybold Optics, Germany. The coating source material was high-purity Ta₂O₅ solid particles deposited on a JGS1 fused quartz substrate. The background vacuum degree of film deposition system was approximately 9×10^-6 mbar, and the vacuum degree during film deposition was approximately 2×10^-4 mbar. The baking temperature of the substrate was 140 ℃, and the evaporation rate of the material was 0.4 nm/s. The film thickness was set to 1500 nm, and crystal vibration monitoring was employed. The auxiliary ion source was the advanced plasma source (APS) from Leybold, which was filled with two channels of argon (Ar) gas as the working gas of the ion source and oxygen (O₂) at a flow rate of 35 mL/min. The discharge current of the ion source was 50 A, and the control range of the ion source bias voltage was 120?150 V. Finally, the deposited Ta₂O₅ monolayer films were annealed under atmospheric conditions. The process parameters for different ion source bias voltages were listed in Table 1.

The Cauchy formula was used to fit the relationship between the refractive index and wavelength, as shown in Figure 2. The figure shows that when the APS bias voltage increases from 120 V to 130 V, the refractive index increases. This may be because the increase in the bias voltage and kinetic energy of the ion beam generated by ionization enhances its bombardment effect on the substrate surface, thus increasing the density of the deposited film. This leads to an increase in the refractive index. Figure 3 shows the relationship between the 1064 nm weak absorption of Ta₂O₅ films and the APS bias voltage. The figure shows that the absorption of the film deposited at 130 V bias voltage is minimal. Figure 6 shows the temperature rise in group A–D samples irradiated by different laser power densities. The temperature rise reflects the strength of the heat absorption capacity of the film; the greater the temperature rise, the higher the absorption loss. As the APS bias voltage increases from 120 V to 130 V, the temperature rise of Ta₂O₅ films under 35 kW/cm² laser power density irradiation decreases from 1.80 ℃ to 1.36 ℃, and significantly increases to 2.27 ℃ when APS bias voltage continues increasing to 150 V. Table 5 shows the contents of the C, O, and Ta elements and atomic ratio of O to Ta in Ta₂O₅ films deposited at different APS bias voltages. As the APS bias voltage increases, the atomic ratio of O to Ta first increases and then decreases. The atomic ratio of O to Ta increases as the bias voltage increases from 120 V to 130 V. This can be attributed to the increase of bias voltage, which produces argon and oxygen ions with higher kinetic energy, enhances the injection effect of oxygen ions, increases the oxidation efficiency, and thus slightly reduces the absorption. Figure 11 shows the root-mean-square roughness of Ta₂O₅ films deposited at different APS bias voltages. The increase in the surface roughness leads to scattering loss, which reduces the reflectivity and causes stray light to affect the beam quality. Figure 13 shows the variation trend of the residual stress in Ta₂O₅ films deposited at different APS bias voltages. When the APS bias voltage is further increased from 140 V to 150 V, the residual tensile stress in the films changes to compressive stress.

Ta₂O₅ momolayer films were successfully prepared via electron beam evaporation and an ion-assisted technique at different APS bias voltages. The multi-dimensional effects of APS bias voltage on refractive index, weak absorption at 1064 nm, temperature rise under continuous laser irradiation, atomic ratio of O to Ta, microstructure, surface morphology, and residual stress of Ta₂O₅ films were investigated. Ta₂O₅ films with higher refractive index, lower surface roughness, better stoichiometric ratio, and lower residual stress are obtained as the APS bias voltage increases from 120 V to 130 V. The XPS test reveals that under the optimal ion-assisted energy deposition state, the stoichiometric ratio of the Ta₂O₅ films is further optimized, and the oxidation degree improves, which directly results in a significant reduction in the absorption loss and temperature rise of the film under continuous laser irradiation. Ta₂O₅ films deposited at different APS bias voltages have amorphous structures. In addition, the APS bias voltage is found to effectively regulate film stress. The stress in Ta₂O₅ films is of tensile type when the APS bias voltage range is 120?140 V. At 150 V, the residual stress changes from tensile to compressive stress, and the surface shape changes from concave to convex. In summary, this study shows that the optimal ion-assisted energy can effectively reduce the absorption loss in the films. In addition, the film stress can be precisely regulated by reasonably adjusting the ion-assisted energy during the film evaporation and deposition. These study findings provide a valuable technological reference for the development of ultra-low absorption loss multilayer laser films in optical systems.