Paraxial Optics

In this chapter, we will consider the properties of optical systems in the region close to the optical axis, usually known as the “paraxial region.” The treatment of light in this paraxial region is referred to as “paraxial optics.” In many texts this region is referred to as the “Gaussian region” and the properties of light in this region are known as “Gaussian optics.” However, in modern optics many scientists and optical engineers working with laser beams with a Gaussian profile also make use of the term “Gaussian optics.” Therefore, we will use the terms “paraxial optics” and “paraxial region” in order to eliminate any confusion. Although we limit our discussion to a small area enclosing the optical axis, paraxial optics is very important. In any well-corrected lens, the rays from outside the paraxial region must intersect the image surface at points very close to the paraxial image points, and we therefore find that many concepts that are strictly defined for the paraxial region are applicable outside of the paraxial region as well.