Quarter Wave Plate
To show properties of a quarter-wave plate.
Bright point source with condenser and iris, yellow filter, two polaroids with quarter-wave plate on insertable mount between them.
Light from a bright point source with condenser and iris passes through a yellow filter and two crossed polaroids onto a distant screen. The quarter-wave plate is then positioned between the two crossed polaroids at any angle except 45 degrees with respect to the crossed polaroids. When the analyzer is rotated periodic minima and maxima of illumination appear on the screen, because the beam is elliptically polarized, and no position of the analyzer will produce darkness. When the polarizer and analyzer are crossed and the quarter-wave plate is set at 45 degrees, rotating the analyzer does not