How does a solid state laser work?
Solid-state lasers date back to the 1960s, with the first laser ever invented being of this variety. The original solid-state laser was a ruby laser that generated an intense flash of blue-white light. The word “laser” means light amplification by stimulated emission of radiation. Technically speaking, lasers do not amplify light, but rather generate it. Laser light has unique characteristics of monochromacy, coherence and directivity.
While semiconductor lasers are often called solid-state lasers, they are actually “diode” lasers, which are their own class of lasers. Solid-state lasers use a solid crystalline material as the “generating” medium. In contrast, other types of lasers use gas, liquids, and semiconductor crystals as the laser medium. Certain atoms found inside the crystal host can be “excited” by external light, a process that produces laser light. The light generated is in a very narrow beam and can be narrowed or manipulated even further, making laser light extremely versatile in many areas, including the healthcare industry and industrial cutting and welding.
Lasers often use ruby, garnet and sapphire crystals in the form of rods. These cylindrical rods are mounted in an optical cavity that forms the bulk of the laser. Solid state lasers consist of the following components:
A solid, crystalline laser medium that can be “pumped” to a higher energy state
A pump system for pumping energy into the laser medium (usually an optical pump system)
A cavity (usually a pair of mirrors mounted at each end of the laser) to reflect the stimulated light through the laser medium
Although the specific components may vary slightly from one laser to another, most solid-state lasers operate on similar principles. Lasers start with the laser medium (and all its atoms, ions, and molecules) in its lowest energy state, which is called the “ground state.”
The energy pumping system stimulates the atoms, ions and molecules of the laser medium to “energy level 2”. At that point, some of these atoms, ions, and molecules will naturally decay, returning to their ground state and emitting a photon of light in a random direction. It is these spontaneous photon emissions and their interaction with excited atoms, ions and molecules that give laser light its unique properties. When a naturally emitted photon and a particle of energy level 2 interact, another photon of light is released. These secondary photoemissions are of the same exact wavelength, phase, and polarization and radiate in the same exact direction.
The light beam generated by this process is monochromatic, with all its waves appearing in step with each other. With a laser, the light is collimated; its rays are parallel.
As the process continues, more and more secondary photons are emitted. Depending on the power of the pump system, light can be generated indefinitely, resulting in a continuous wave laser. Less capable pumping sources cannot sustain unlimited light generation; thus they lead to pulsed lasers. In both cases, solid-state laser light can be manipulated and used in a variety of applications.
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