Facile liquid phase deposition of thick reflective GeO₂ film for hollow waveguide delivery of CO₂ laser radiation

A new idea of using LPD (liquid phase deposition) to prepare a GeO ₂ thick reflective film for hollow waveguide delivery of CO ₂ laser radiation was investigated in this work. The LPD process was achieved by designedly adding acid to GeO₂-aqueous ammonia. The addition of acid could induce the transformation of germanate ions into GeO ₂ solutes, leading to the deposition of a GeO₂ ceramic film when the concentration of GeO₂ solute is higher than its saturation solubility. It was found that the highest film growth rate occurred at a pH value of 3, while a film with low surface roughness and good adhesion to the substrate was produced at a pH value of 2 and the film could be converted to a smooth, compact hexagonal GeO₂ film by heat treatment at 1120 °C for 30 min. Two abnormal dispersion bands within 7.6-9 μm and 9.6-11.2 μm were mainly caused by the silica glass substrate and the GeO₂ film, respectively. The film was thick enough to achieve the total reflectance of the CO₂ laser radiation. The use of this GeO₂ film in a hollow waveguide structure for CO₂ laser radiation delivery is discussed based on the transmission loss and the feasibility of the deposition of the GeO₂ film inside silica capillary tubes. The results show that the hollow waveguides with low transmission loss are most likely fabricated at a low cost using the LPD-derived GeO₂ reflective film.