The substance whose excited atoms, ions or carriers provide the stimulated emission. Its choice sets the laser's wavelength, gain bandwidth, energy storage time and thermal behavior: Nd:YAG at 1064 nm stores energy well for Q-switching, Ti:sapphire's broad bandwidth supports femtosecond pulses, and Yb-doped fiber handles kilowatts because heat spreads along meters of glass.
Same cavity, swap the gain medium from Nd:YVO4 to Nd:YAG and you trade some gain for a lot more stored energy.
Also heard as
- active medium
- laser medium
- gain material
Related terms
Pump
The energy source that excites a gain medium, or the act of supplying it, usually with diodes, flashlamps or current.
Population inversion
The condition where more atoms occupy the upper laser level than the lower one, which a medium needs to give gain.
YAG
Shorthand for yttrium aluminum garnet, and in practice for the Nd:YAG laser at 1064 nm.
Ti:sapph
Titanium-doped sapphire, the broadband tunable laser crystal behind most femtosecond oscillators and amplifiers.
Fiber laser
A laser whose gain medium is an optical fiber with a rare-earth-doped core, pumped by diodes.