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 GeO2 thick reflective film for hollow waveguide delivery of CO2 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 GeO2 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 degrees C for 30 min. Two abnormal dispersion bands within 7.6-9 mu m and 9.6-11.2 mu m 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.