What is a Solid-State Laser?

What is a Solid-State Laser?

A solid-state laser consists of a gain medium that is a solid, rather than a liquid as used in dye lasers or the gas that’s in a gas laser. The gain medium of a solid-state laser consists of a glass or crystalline host material (e.g., a few mm in diameter cylindrical rod in an Nd:YAG or disk shape in a thin disk laser). This host material must be doped with either transition metal ions (e.g., titanium – Ti³⁺ for Ti:Sapphire lasers) or rare earth ions (e.g., neodymium – Nd³⁺, ytterbium – Yb³⁺, or erbium Er³⁺). There are many host materials in which laser excitation has been achieved, but relatively few types are in widespread use. Of these, the most common ones are neodymium-doped yttrium aluminum garnet (Nd: YAG crystal), neodymium-doped yttrium lithium fluoride (Nd:YLF), neodymium-doped glass (Nd:glass), and either erbium-doped or ytterbium-doped glasses (Er:glass / Yb:glass). 

The gain medium is typically optically pumped using either a flashlamp, or laser diodes by side-pumping or end-pumping. Typically, flashlamp-pumped lasers are lower cost and can provide high power output. Though, these pump sources usually exhibit low power efficiency levels, relatively shorter lifetimes (must replace the flashlamp more often than when optical pumping with diodes), and they are prone to causing thermal lensing effects in the gain medium. Diode-pumped solid-state (DPSS) lasers tend to be more efficient and compact, with lower overall maintenance, longer lifetimes, and provide better beam quality. Recently solid state DPSS lasers have become more common as the cost of high-power laser diodes has gone down, allowing more people to benefit from solid state laser advantages.

Semiconductor Lasers are also classified as solid-state lasers, but are considered a separate class or type of solid-state lasers and are often called Laser Diodes or Diode Lasers.  Laser Diodes use electrical power as an energy source and doped p-n junctions as a gain medium. The front facet is a partial reflector, and the back facet is the total reflector. Therefore, the front facet is the output facet of the laser emission.