Lasers have come a long way since their inception, and their applications seem to grow by the day, furthering developments in medical, security, education, and other fields. However, for lasers (light amplification by stimulated emission of radiation) to be this effective, they do not work alone. Instead, they require a gain medium as well as an optical feedback system. These together make up the laser systems that have fast become popular across the globe.

So, what is a gain medium? Laser energy must move through a gain medium for the stimulation of electromagnetic radiation to occur. After this, the resultant beam can then reflect in an optical cavity prior to leaving the cavity and moving towards the target point.

This working mechanism is standard, and without it, lasers cannot work as they do as they would not have the gain medium to stimulate electromagnetic radiation. You may have come across gain mediums but had no idea what they were. Often, manufacturers will classify their lasers based on the gain mediums. They can be gas, solid, semi-conductors, and even liquids.

Laser crystals are solid mediums, and these have fast become popular among manufacturers and laser users worldwide. We will cover how they work and why manufacturers and users alike may prefer these to other types of mediums.

What are laser crystals?

Laser crystals combine various iron types in each medium, which is not seen in other kinds of mediums, thus giving them an edge over the competition. They have much less absorption, exhibit higher transitions cross-section, and have much better thermal conductivity. Overall, these characteristics make them more efficient as far as transmission goes, making them ideal for applications that rely on high precision. Additionally, they are available in an array of shapes, and users can choose what works for their optical systems, which brings us to the next point:

What are host crystals?

Not all crystals can host ions and manage to work under extreme conditions inside the laser cavity. The medium chosen affects the gain bandwidth, upper state lifetime, and transition wavelength.

For example, compared to Nd: YAG, Nd: YVO4 crystals have much more gain bandwidth, higher cross-sections, and smaller upper state lifetimes.

Image credit: Eksma Optics

For a crystal to perform such a role, it must be highly transparent as this ensures that absorption and scattering remain at a minimum to avoid loss of efficiency. Additionally, the crystal must withstand harsh conditions without falling apart; else, it will be of no use in the optical system.

When working with high-power lasers, users seek crystals with high thermal conductivity low thermo-optic coefficients and high resistance to mechanical stress. While these factors are also crucial in medium and low power applications, they tend to hold more water with high power applications.

Based on each crystal’s capability, manufacturers group their laser crystals based on their features and their applicability. Users can then assess what components are essential to building an optical system that can meet their needs.

Types of Laser Crystals

The composition of a crystal will ultimately determine where best it’s suited. That’s why many manufacturers choose to name their crystals based on their compositions which start with the doping ion followed by the host crystal. For example, Nd: YAG refers to a neodyium doped Yttrium aluminum garnet crystal. Often, the main host crystals are garnets, fluorides, sapphires, vanadates, and chalcogenides. You can visit EKSMA Optics to see the variation in laser crystal types and their corresponding features and applications.

Forms of Laser Crystals

As earlier mentioned, laser crystals come in different shapes, which is to the advantage of the user, who can determine what the best option per application is. More often than not, people go for cuboids. However, there are many other variations in the market, with the most common being: Crystals with extreme angles on both sides

  • Slab lasers which may take on cuboid shapes
  • Thin discs with very small thicknesses
  • Composite crystals which come in unique shapes
  • With various other shapes in the market, users can also request unique shapes based on the optical system in play.

When choosing laser crystals, a user must consider the application at hand. Additionally, the user must consider the optical transparency, linear absorption, birefringence, chromatic dispersion, and the magnitude of the deff, among other essential factors. The ability of the crystal to withstand optical and photoreactive damage also plays a vital role in this decision.