The document describes the Michelson Interferometer, which uses a laser, two mirrors (one movable), and a beam splitter to create interference patterns. Light from the laser is split by the beam splitter, reflected by the mirrors, and recombined to produce alternating bright and dim fringes as one mirror is moved. The changing fringe pattern is used to determine the laser's wavelength, with each fringe corresponding to a path difference change of one wavelength.

1. The Michelson
Interferometer
LO9 PHYSICS 101

2. • With the aid of two mirrors, light is brought to
interference.While moving one of the mirrors, the
alternation in the interference pattern is observed
and the wavelength of the laser light is determined.
• From a the Michelson Interferometer we can learn
about interference, wavelength, diffraction index,
and phase.

3. • The set-up includes a laser
(a source of monochromatic
single wavelength light), 2
mirrors at 90 degrees (one
is moveable), a beam splitter
that reflects 50% of the light
and lets 50% through, and a
compensator plate that
makes the total distance
that each beam travels
equal.
How is the apparatus
set up?

4. How do we create an
interference pattern?
• If the two paths are
equal in length and we
gradually adjust the
moveable mirror, the
image at the detector
goes from bright (zero
path difference) to dim
(a path difference of one
half wavelength) to
bright again and so on.

5. What does this pattern
tell us?
• The change in path difference
is twice the distance d that
the mirror moves because the
light must travel to the
moveable mirror then back to
the splitter.
• In order for an intensity
maximum at the detector
(constructive interference) the
condition m =2dλ where m is
any integer must be satisfied.

6. What does this pattern
tell us?
• A path difference of 0
will result in
constructive
interference while a
total path difference of a
half wavelength will
produce complete
destructive interference.
• The alternating light and
dark rings produced are
called fringes (m).

7. TestYour
Understanding
• You shoot a laser of unknown wavelength
using a Michelson Interferometer and slowly
move the adjustable mirror at a steady pace
to produce even fringes.
• You notice that after a change in position of
the mirror of 726nm, you are able to count
around 11 fringes on the photodectotor.
What must the wavelength of the light source
be?

8. Solution
• Since m =2dλ and we know that the change in
position of the mirror was 726nm and resulted in
11 fringes, we can solve for the remaining unknown
which is the wavelength of this laser.
• =(2*726nm)/11=132nmλ

9. Image Sources
• #1:http://www.academia.edu/7006694/Interferometer
• #2:
http://www.phy.davidson.edu/stuhome/cabell_f/diffractionfinal/p
• #3:
http://electron6.phys.utk.edu/optics421/Laboratories/Lab7.htm
• #4:
http://opticalengineering.spiedigitallibrary.org/article.as
px?articleid=1088823

10. Thank you for watching!