Meaning of half-wave plate

half'-wave plate'

Pronunciation: (haf'wāv", häf'-), [key]
— Optics. Optics.
  1. a crystal thin enough to cause a phase difference of 180° between the ordinary and extraordinary rays of polarized light, thereby changing the direction of the plane of polarization. Cf.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.