Every beam of light has certain divergence while it propagates.

For most applications it is better to reduce the beam divergence.

Divergence means that, as the beam propagate, the same amount of radiation spread over larger area. Thus reducing the power density and the effectiveness of the radiation.

Lasers are the radiation sources with the least divergence available.

The sections of this chapter are:

7.2.1 Divergence Angle.
7.2.2 Near Field and Far Field.
7.2.3 Rayleigh Range, and Gaussian Beam divergence.
7.2.4 Diffraction through a Circular Hole.
7.2.5 Fresnel Number.
7.2.6 Beam Focusing.