Mirror
--------- /-\
Beam Splitter | /\//
\ | |-\\\ Material
\ | /-\\\\ Under
+------+ \ |/ \--//- Test
|Laser |----------/------------ \-\||
+------+ /| /-/|/
| |////
| \\/\
|
+-----------+
| Detector |
| |
+-----------+
Collimated laser light is emitted from a source onto a
beam splitter. Half the light
impinges onto the material being tested. Half the light is directed to a
mirror. The light beams from the mirror and material under test recombine at the
detector.
Constructive and
destructive interference between the beams, caused by variations in the
pathlength of the light, are observable by differences in the
amplitude of the light at the detector. Michelson interferometers are remarkably useful and ubiquitous devices for small-scale measurements of a wide variety of properties.