Optics > Polarization > Polarization by Double Refraction DCS# 6H35.40

QUARTER WAVE PLATE


APPARATUS
quarter wave plate 202-21-C
two polarizers 202-21-D3
yellow filter 202-21-D3
mirror 101-06-E2


DESCRIPTION
Place the interference filter on the document camera's slide viewer followed by two crossed polarizers so no light is transmitted.  Insert the quarter wave plate between the polarizers with its axis at 45°.  The light emerging from the quarter wave plate is circularly polarized, so the analyzer no longer blocks the light and some light is transmitted.  Rotating the analyzer has no effect on its intensity.

If a second quarter wave plate is inserted after the first, the beam can again be blocked.

Set the quarter wave plate at any angle except 45° and the emerging beam will be elliptically polarized.  Intensity minima and maxima are seen as the analyzer is rotated, but no position of the analyzer will completely extinguish the beam.

Place the quarter wave plate between a polarizer and a mirror.  Upon reflection, the circularly polarized light changes handedness and, after returning through the quarter wave plate, the beam is plane polarized 90° from its original direction and does not pass through the polarizer.