Compound prism

A compound prism is a set of multiple triangular prism elements placed in contact, and often cemented together to form a solid assembly. The use of multiple elements gives several advantages to an optical designer:

• One can achieve spectral dispersion without causing the deviation of the beam at the design wavelength. Thus, light at the design wavelength which enters at an angle ${\displaystyle \theta _{0}}$ with respect to the optical axis, exits the prism at the same angle with respect to the same axis. This kind of effect is often called "direct vision dispersion" or "nondeviating dispersion".
• One can achieve deviation of the incident beam while also greatly reducing the dispersion introduced into the beam: an achromatic deflecting prism. This effect is used in beam steering.
• One can tune the prism dispersion to achieve greater dispersion linearity or to achieve higher-order dispersion effects.