S

The spot size of a beam is the beam diameter in free space. It varies along the length of the beam according to the equation:

𝜔_𝑧.= 𝜔₀.,-1+,,,𝑧-,𝑧-𝑟...-2..

Where

,𝑧-𝑟.=,𝜋,𝜔-0-2.-,𝑟-2..

And ω₀ is the beam diameter at r=0, which is the minimum beam experienced by the beam.

Related Terms: Acceptance Angle, Core, Mode Field Diameter (MFD), Numerical Aperture (NA)