An optical gain medium (also called an "active laser medium") can make light stronger. In general, gain media must be powered by another energy source in order to have energy to provide as light. Some gain media can be powered using electricity, but many others need light energy from bright flash lamps or a laser. Optical gain media are used in lasers. The first lasers used artificial ruby as their optical gain medium.= = = Microvillus = = =
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