7
012-09200A Polarization Analyzer
Verify Malus’ Law of Polarization
Introduction
The purpose of this laboratory activity is to determine the relationship between the intensity of the transmitted
light through two polarizers and the angle, Ø, of the axes of the two polarizers.
Theory
A polarizer only allows light which is vibrating
in a particular plane to pass through it. This plane
forms the “axis” of polarization. Unpolarized
light vibrates in all planes perpendicular to the
direction of propagation. If unpolarized light is
incident upon an “ideal” polarizer, only half will
be transmitted through the polarizer. Since in
reality no polarizer is “ideal”, less than half the
light will be transmitted.
The transmitted light is polarized in one plane. If
this polarized light is incident upon a second
polarizer, the axis of which is oriented such that
it is perpendicular to the plane of polarization of
the incident light, no light will be transmitted
through the second polarizer.
However, if the second polarizer is oriented at an
angle so that it is not perpendicular to the first
polarizer, there will be some component of the
electric field of the polarized light that lies in the
same direction as the axis of the second polarizer,
thus some light will be transmitted through the second polarizer (see the bottom figure).
The component, E, of the polarized electric field, E
o
, is found by:
=
0
cos
Since the intensity of the light varies as the square of the electric field, the light intensity transmitted through
the second filter is given by:
=
0
cos
2
where I
o
is the intensity of the light passing through the first filter and Ø is the angle between the polarization
axes of the two filters.
EQUIPMENT NEEDED
– Basic Optics Bench (part of OS-8515) – Light Sensor (CI-6504A or PS-2106)
– Basic Optics Light Source (part of OS-8515) – Rotary Motion Sensor (CI-6538 or PS-2120)
– Polarization Analyzer with Aperture Bracket (OS-8533A)
Figure 1.1: Polarization
Polarizer 1
Polarizer 2
unpolarized light
polarized light, I
0
I = I
0
cos
2
φ
φ
component of polarized light parallel to
axis of Polarizer 2
(14 pages)
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