The document describes the Michelson interferometer experiment. It explains that a laser beam is split by a half-silvered mirror, with one beam striking a fixed mirror and the other a movable mirror. The beams are recombined, producing an interference pattern due to the phase change from the altered path length of the movable mirror. Adjusting the movable mirror varies the path lengths and results in different interference patterns, which can be used to make distance measurements by counting the fringes. Applications and examples of using the Michelson interferometer to determine wavelength and distance are also provided.

1. Physics 101
THE MICHELSON
INTERFEROMETER

2.  Electromagnetic waves interfere with each other in the
same way as mechanical waves:
 Waves with the same frequency will interfere constructively
when in phase and destructively when out of phase.
 Lasers produce light that is monochromatic (single
wavelength) and coherent (same phase).
 The phase difference required for complete destructive
interference on waves with equal intensity, frequency
and polarization is described by a fraction of a
wavelenght
 λ/2 = π rad = 180’
INTRODUCTION

3.  The purpose of the Michelson Interferometer experiment is to
produce interference fringes by splitting a beam of light.
 A beam of light is split by a silvered plate, one on the half-
beams strikes a fixed mirror, and the other a movable mirror.
 The beams are brought back together and an interference
pattern is produced. This is due to the phase change caused
by the altered path length by the movable mirror.
 Moving a mirror ½ a wavelength changes the phase of half
beam by one wavelength.
THE EXPERIMENT
(Hyperphysics)

4.  By adjusting the movable mirror the wavelength is changed
and different path lengths are produced.
 Constructive interference (intensity maximum) is given by:
m λ = 2d
 The Michelson Interferometer can be used to make distance
measurements by moving the mirror and counting the
interference fringes which move by a reference point.
( Hyperphysics)
 The distance d associated with m fringes
is given by:
d= m λ / 2
APPLICATIONS

5.  “The fringes for wavelengths λ = 632.8 nm and 420 nm are
shown above. As the magnitude of the path difference increases
the fringes move outward while as the magnitude of the path
difference decreases the fringes move inward.” (fp.optics)
UNDERSTANDING THE CONCEPT
(fp.optics)

6.  You are studying different lasers in your physics tutorial. You
are told that the beam of light produces 480 fringes in a
distance of .33 mm. Find the wavelength
 Using m λ = 2d
 2 d = 480 λ
λ = 0.66 mm/480
λ = 1.375 µm = 1290 nm
IN THE LAB

7.  This time you are given a laser and told its wavelength is
376nm. Your lab partner manages to count 534 fringes. What
is the distance?
 Using m λ = 2d
 Convert 576nm to 0.00576
 0.00534 (376) = 2 d
 d= 2.00784/2
 d= 1.000392
IN THE LAB

8.  http://hyperphysics.phy-
astr.gsu.edu/hbase/phyopt/michel.html#c1
 http://fp.optics.arizona.edu/jcwyant/JoseDiaz/MichelsonInter
ferometerFringes.htm
SOURCES