The Michelson interferometer uses a laser light source that is split by a beam splitter into two beams. One beam reflects off a fixed mirror and the other reflects off a movable mirror before recombining at the detector. By moving the movable mirror, the path length of one beam can be varied, causing the beams to interfere constructively or destructively at the detector and creating bright or dark fringes. This allows very small changes in distance or wavelength to be measured precisely.

1. Michelson Interferometer
Physics 101

2. Purpose
• Used to observe wave interference
• Measures small shifts in distance/wave speed

3. Set Up
• Key elements:
– Light source (ie. Laser)
– Beam splitter (partially silvered mirror)
– Detector
– Movable mirror
– Glass compensator
– Fixed mirror

4. Light Trajectory
• Beam splitter splits the beam from the source into 2
• Beam 2:
– Passes through beam splitter
– Reflects off the fixed mirror
– Reflects from the splitter to the detector
– *Compensator is used if the silvered edge of the beam
splitter is facing away from the source*
• Beam 1:
– Reflects of edge of partially silvered mirror
– Bounces off movable mirror
– Passes through beam splitter and hits the detector

5. Light Trajectory
Compensator
Movable Mirror
Fixed Mirror

6. Applications
• Splitting beam and sending it along 2 different
paths of different lengths  phase difference
• Speed of both beams a vacuum = c (speed of
light)
• Moving the movable mirror changes the distance
travelled by beam 1
– Image at detector will alternate between bright and
dim as path difference increases from 0λ to 0.5λ to 1λ,
etc…
– Path difference = 2(distance mirror is moved)

7. Applications
• Maximum intensity at detector (constructive
interference: mλ=2d
– m= an integer
– λ= wavelength of light
– d= distance mirror is moved
– 0λ path difference  constructive interference 
disk of light at detector
– 0.5λ path difference  destructive interference
• Bright disk for integer multiples of wavelength
• Dark disk for m+0.5 multiples of wavelength

8. Output Images