Etching of silica glass under electric fields

The etching rate of silica glass in 40% hydrofluoric acid under the influence of electric fields is studied with the help of an interferometric technique. A linear dependence of etching rate with field strength was found, with a similar to 2.5% etching rate change for an applied field of 20 MV/m. The experimental results are compared with those of a simple model that attributes this dependence to partial orientation of the HF molecules in the electric field. The measured dependence is sufficiently significant to account for the selective etching observed in frequency doubling glasses and fibers.