Meaning of quarter-wave plate

quar'ter-wave plate"

Pronunciation: (kwôr'tur-wāv"), [key]
— Optics. Optics.
  1. a crystal thin enough to cause a phase difference of 90° between the ordinary and extraordinary rays of polarized light, thereby converting circularly polarized light into plane polarized light. Cf.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.