The main materials of prisms are BAK4 and BK7. The refractive indices of these two types of glass are different. BAK4 has a high refractive index. For a Paul prism made of BAK4, it can completely reflect 100% of the incident light without considering absorption, while BK7 can only reflect about 83% of the incident light. Therefore, BAK4 has a high optical efficiency, but its price is also very high.
