Erbium activated phosphate laser glass, or Er:glass, is a type of glass that is doped with the rare earth element erbium. This glass material is used as a laser medium in certain types of lasers, particularly erbium-doped fiber lasers (EDFLs) and erbium-doped waveguide amplifiers (EDWAs). The presence of erbium ions in the glass allows for the absorption and stimulated emission of light at specific wavelengths, which can be used to generate laser light. The use of Er:glass in EDFLs and EDWAs has become increasingly popular due to its high gain, low noise, and efficient energy transfer, making it a key component in many communication and industrial applications.