Definition and introduction to solid-state lasers
Tuesday, December 20, 2022
Lasers that use crystals or glass as their lasing medium are known as solid-state lasers.
Solid-state laser technology has granted us lasers that are powerful, span a wide range of wavelengths, and can operate in various modes.
Why use crystals?
The glasses and crystals are chosen for their durability, optical properties, and capacity to evacuate heat. However, modern solid-state lasers usually do not rely on the crystal itself for lasing. Rather, the crystal or glass acts as a host structure for the atoms (known as dopants) that are responsible for laser action.
Some common examples are Nd:YAG, Nd:glass, Yb:YAG and Ti:Sapphire lasers. In each of these examples, the active Neodymium (Nd), Ytterbium (Yb) or Titanium (Ti) dopant is embedded in a garnet (Yttrium-Aluminum Garnet), sapphire, or glass.
Available modes of operation
Solid-state lasers can be used in all of the main laser operation modes (CW, pulsed, ultrafast).
Crystals typically have better thermal conductivity than glasses. This makes them better suited for CW lasers, since these lasers continuously operate, and therefore continuously need to evacuate heat.
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Solid-state laser lasing mediums tend to have long upper-state lifetimes. This makes it easier to accumulate potential energy in the excited atoms and facilitates the generation of Q-Switch pulses, both in glasses and crystals.
The inhomogeneous nature of glasses broadens the spectrum of available transitions. This makes glass-based solid-state lasers better for generating ultrashort pulses (i.e. mode-locked).
Methods of optical pumping
The host crystals and glasses are not typically electrically conductive, making optical pumping the predominant method of pumping.
Flash and Arc lamp pumping
Historically, flash or arc lamps were placed all around the lasing medium to provide energy to the system and prime it for laser action. Flash and arc lamps are cheap and can supply a lot of pump energy. They are still used today when high-energy, low-repetition pulses are required.
A big disadvantage of lamps is their high heat output. Lamps emit many different wavelengths, but only a small minority are useful for pumping the laser. All the other wavelengths are wasted and turn into heat. This heat needs to be evacuated by waiting between pulses, by adding active cooling systems, or both.
Laser diode pumping
Laser diodes can emit just the specific wavelengths useful for pumping, greatly reducing wasted pump energy. Often, heat production is reduced enough for bulky cooling systems to be removed completely. The removal of the cooling systems, combined with the small size of laser diodes, makes diode-pumped solid-state lasers very compact setups.
Diode-pumped solid-state (DPSS) lasers also present less noise and better beam quality at low power. By combining diodes in arrays, stacks, and bars, high output powers can also be obtained (though the beam quality does decrease in this case).
We hope you’ve enjoyed this introduction to solid-state lasers. As always, you are welcome to ask questions about your setup to our knowledgeable staff.
