Glass serves a critical function in diverse technologies ranging from medicine to telecommunications. Fax machines and text scanners use micro-optic lens arrays made from ion-exchanged, gradedindex glass to image original documents. Data for long-distance communication by telephone or computer are transmitted in the form of modulated laser light through highly transparent glass fibers. These signals are boosted for long-haul transmission by stimulated emission in erbium-doped glass optical amplifiers. Lap-top computers use flat-panel-display glass in their liquid-crystal screens (see “Materials for Flat-Panel Displays,” MRS Bulletin, March 1996). Gall-bladder and hysterectomy surgeries have been made minimally invasive in part because of slender glass imaging endoscopes.

Functionality in glass is expanding rapidly. New properties are often attributable to new defect species created by strong optical or electrical fields. For example rare-earth-doped ZBLAN glass (a commercial fluoride glass), when exposed to high peak-intensity femtosecond laser pulses, becomes phosphorescent. (See the cover of this issue.) The phosphorescence is visible to the naked eye up to 12 hours after illumination. Other compositions show similar effects. Phosphorescent glasses are transparent and may be more easily formed into contiguous films and fibers than powder or microcrystalline phosphors.