Solid-state laser

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A solid-state laser uses a solid material (a crystal or glass) as the laser medium. It does not use a diode as the gain medium, which is treated as a separate class of lasers.

How it works
- The active medium is a host material with a dopant ion (such as neodymium, chromium, erbium, thulium, or ytterbium). These rare-earth dopants work well because their excited states aren’t strongly affected by the crystal’s vibrations.
- There are many solid-state media, but a few are common. Nd:YAG (neodymium-doped yttrium aluminum garnet) is the most widespread. Nd:glass and ytterbium-doped glasses or ceramics are used for very high-power work, like certain fusion experiments.
- The first laser materials were synthetic ruby. Ruby lasers are less common today due to lower efficiency, though they can produce continuous output at very low temperatures.
- Other early solid-state media include uranium-doped calcium fluoride, which lasered at 2.5 micrometers.

Tuning and pumping
- Some solid-state lasers can be tuned to different colors using special intracavity components (etalons, prisms, gratings). Ti:sapphire covers a broad range (roughly 660–1080 nm); Alexandrite covers about 700–820 nm and can deliver high-energy pulses.
- The lasers are usually pumped optically, using flashlamps or arc lamps, or by laser diodes. Diode-pumped solid-state lasers (DPSSL) are more efficient and have become common as high-power diodes have become cheaper.

Pulses and applications
- Solid-state and related lasers can produce very short pulses (mode-locked). This often uses saturable absorbers such as SESAMs or SWCNTs; graphene has also been used.
- Applications include research, medicine, and military uses. Passively Q-switched solid-state lasers are useful for ranging, 3D imaging, removing material (photoablation), and laser-induced breakdown spectroscopy.