In this chapter, we will consider the properties of optical systems in the region close to the optical axis, usually known as the âparaxial region.â The treatment of light in this paraxial region is referred to as âparaxial optics.â
In many texts this region is referred to as the âGaussian regionâ and the properties of light in this region are known as âGaussian optics.â However, in modern optics many scientists and optical engineers working with laser beams with a Gaussian profile also make use of the term âGaussian optics.â Therefore, we will use the terms âparaxial opticsâ and âparaxial regionâ 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.
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