Hey...
active lasermedium: Within alaser, thematerialthat emits coherent radiation or exhibits gain as the result of electronic or molecular transitions to a lower energy state or states, from a higher energy state or states to which it had been previously stimulated.
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Hello Aspirant,

Within a laser, the material that emits coherent radiation or exhibits gain as the result of electronic or molecular transitions to a lower energy state or states, from a higher energy state or states to which it had been previously stimulated.

Examples of active laser media include certain crystals, gases, glasses, liquids, and semiconductors.

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Have a good day!!