Transcript Interference of Light: Applications to Interferometry

INTERFERENCE OF LIGHT:
Applications to Interferometry
Course
Grade 12 Physics
Time Required
Two 1-hour lessons
PA Standards Met
3.4.12.C:
Evaluate wave properties of
frequency, wavelength and
speed as applied to sound
and light through different
media.
Principles
 Since light has wave properties, it will
experience interference (the addition of
waves).
 This interference is like that seen with
water waves.
 Whether you get constructive or
destructive interference depends on the
wavelength of the light.
 White light is made up of many colors.
These different colors have different
wavelengths.
Interference as commonly observed:

We can see the many colors of light on
soap bubbles.

The separation of white light into many
colors on a bubble happens because of
interference.
Chromatic interference is seen in nature, such
as in sea foam, which is made of plankton.
The following is an animation of interference of
waves coming from two point sources:

Green metallic-like reflection of a
photographic flash from the eyes of a cat,
caused by multiple thin-film interference.

Scales of stomatopod crustaceans viewed
with different angles of a polarizing filter.
Photos taken a few moments apart
Making Use of Interference of Light:

Interferometry is a technique of using the
pattern of interference created by the
superposition of two or more waves to diagnose
the properties of the aforementioned waves.

Interferometry makes use of the principle of
superposition to combine separate waves
together in a way that will cause the result of
their combination to have some meaningful
property that is diagnostic of the original state of
the waves.

This works because when two waves with the same
frequency combine the resulting pattern is determined by
the phase difference between the two waves: waves that
are in phase will undergo constructive interference while
waves that are out of phase will undergo destructive
interference.
A
B
A = Combined wave form of initial waves in phase
B = Destructive interference resulting from waves out of phase.
How an Interferometer works:

The instrument used to ‘interfere’ the waves
together is called an interferometer.

Most interferometers use light or some other
form of electromagnetic wave.
Illustration: Mach-Zehnder Interferometer
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Interferometry is an important investigative
technique in astronomy, plasma physics, fiber
optics, engineering metrology, optical metrology,
oceanography, seismology and quantum
physics.
The following is an interference pattern
produced with a Michelson Interferometer:
Interferometer: Application to
Nanotechnology


When the wavelength of the light used is known,
small distances in the optical path can be
measured by analyzing the interference patterns
produced. This technique is used to measure
the surface contours of materials, making it
possible to study materials at the nanoscale
level.
Nanotechnology has been used to produce
novel structures and films with wide and useful
applications.
Who makes Interferometers?
University of Pennsylvania, SEAS Lab: Uses one
supplied by the Zygo Corporation. They conduct
lots of nanotechnology experiments.
LAB ACTIVITY: ‘DESIGNING’ AN
INTERFEROMETER
SCHEMA 1:
SET-UP:
ACTIVITY:
“HOMEMADE INTERFEROMETER FOR $ 20”
Adopted from “Metacafe Video
Entertainment / Celtic Mad Scientist”
 AV DISPLAY

THE END