## Pilot beam

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:

{!{!{A\le2f'+\frac{\emptyset_{beam}^2\cdot\pi}{4\lambda}}!}!}

where Ø_{beam} is the collimated beam diameter.

The optimum position of the beam waist is defined as distance A2.

{!{!{A2=\frac{A}{2}}!}!}