0 7 0 9 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 2 3 4 3 6 3 8 3 9 4 0 4 2 4 4 4 6 4 8 5 0 5 2 5 4 5 6 or 5 8 mole other conventional additives are to be avoided chiefly elements such as refining agents i e as 2 o 3 and sb 2 o 3 and antisolarants sb 2 o 3 and nb 2 o 5 which can during ion exchange of alkali for silver generate silver metal colloidal particles in the glass which leads to a waveguide exhibiting high loss absorption and poor optical quality scattering centers the laser phosphate glass composition described above is useful for the preparation of a glass optical waveguide which can then in turn be used in e g optically pumped lasers for example the glass could be used to provide a plate waveguide wherein a certain region of the glass plate is treated e g by ion exchange to provide regions having different refractive indexes such that light will be guided through a specific region of the glass plate these waveguides can be fabricated by a variety of means in which silver is preferentially substituted for sodium and to some extend other alkali ions in the glass through techniques such as molten salt bath ion exchange and electric field assisted migration from solid silver films ion exchange is conducted at elevated temperatures e g about 350 u00b0 c.