Nb2O5 deposited by ion-assisted reactive magnetron sputtering for near-infrared optical coating: Power modulation and performance degradation

Nb2O5 exhibits outstanding optical properties within the near-infrared spectra, suggesting considerable potential for application in optical coatings. In this work, Nb2O5 was deposited by ion-assisted reactive magnetron sputtering. The potential of sputtering power modulated various properties of Nb2O5 was revealed. The results showed that the deposition rate rose up to 2.05 angstrom/s with increasing power. Optimal deposition of amorphous Nb2O5 was achieved at 450-600 W, exhibiting a defect-free surface and cross-section, accompanied by a minimal roughness of 0.36 nm and a consistent refractive index range of 2.10 to 2.35. These Nb2O5 demonstrated excellent optical performance in the near-infrared band. The reflectance of high-reflective coatings achieved 99.8 %, and the reflectance of antireflective coatings achieved 0.06 %. NbO2 was successfully deposited at 900 W, presenting a promising method for large-scale NbO2 deposition, independent of precise oxygen control. The high-temperature performance of Nb2O5 was evaluated, and the results showed significant crystallization at 750 degrees C, inducing a substantial rise in defects and surface roughness, exceeding 6 nm. The optical properties of Nb2O5 were affected, resulting in high-temperature performance degradation in optical coatings. Specifically, the reflection spectra of anti-reflective coatings experienced a 48 nm shift. The reflectance of high-reflective coatings decreased from 99.8 % to 41.2 %, and was accompanied by a blue shift exceeding 80 nm in the near-infrared band. The critical temperature of this dramatic change was identified to be within 450-550 degrees C. Typical catastrophic optical damage on the laser facet was observed. These findings provide valuable insights for the application of Nb2O5 optical coatings in near-infrared lasers.