A pilot beam is a Gaussian beam of essentially constant diameter over a particular working range A and is attainable using fine adjustment.
Determining the pilot beam working range and position of the beam waist
Beam path of the pilot beam exiting a single-mode fiber with angled connector FC APC.
The maximum working range A of a pilot beam is limited because of diffraction:
where Øbeam is the collimated beam diameter.
The optimum position of the beam waist is defined as distance A2.