Paratellurite is a mineral form of tellurium dioxide (TeO2) and is commonly used as an acousto-optic crystal. It is characterized by its high refractive index and good optical clarity, making it an ideal material for acousto-optic applications such as beam steering, frequency filtering, and modulation. Paratellurite has a high acoustic velocity and a high electro-optic coefficient, making it a useful material in both low and high frequency acousto-optic devices. The crystal is also highly stable, which is important for long-term applications in high power optical systems. However, paratellurite is relatively rare and is difficult to fabricate in large crystals, making it a relatively expensive material compared to other acousto-optic materials.