Their ability to transmit, rather than absorb, infrared light is useful in developing laser surgery instruments and optical materials for infrared laser and window applications. For optimal control, they use aerodynamic forces to overcome gravity, and acoustic forces to control and stabilize the position of the sphere. Cameras and other instruments record the behavior of the levitated sample. The sample is then heated and melted with a carbon dioxide laser beam with up to 500 watts of power. When the liquid drop is cooled to the material's melting point and below, a number of things can happen.
Most materials begin to solidify, forming crystals, especially if the liquid is in a container.
Since transparent glass is the goal for CRI, it is important to avoid crystallization. Instead of crystallizing as they are cooled below the melting point, the levitated oxides begin to become viscous, like maple syrup. Under normal circumstances, compounds based on aluminum oxide form liquids that aren't at all viscous near the melting point. You can access metastable viscous states that you wouldn't normally see. When you have a solid surface, like a container, in contact with a liquid, it promotes crystallization.