Before the beam

(Naut.) in an arc of the horizon included between a line that crosses the ship at right angles and that point of the compass toward which the ship steers.

See also: Beam

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Here |[[psi].sub.t]> = |p> since before the beam splitter BS1 the beam is clearly localized as seen from the second loop of the interferometer.
A main purpose of such procedures is to measure noise -- that is, fluctuations in the amplitude of the light -- before the beam is sampled by some detector.