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.