Michelson Interferometer
(A Processing program for visualising interference)
Charlotte Bond
summer project
2009
The applet below illustrates the interference of optical waves in a Michelson interferometer.
You can change the length of one interferometer arm and observe how the light power in the two
interferometer output changes. You can also play with the reflectivity of the beam splitter or the mirrors
to understand their effect on the interference. If you want to know how light fields are reflected
or transmitted at an optical surface, have a look at my other applet: Reflection!
In this sketch the light is depicted as waves. Using the tick box `play waves continuously'
you can choose to have static or travelling waves. The amplitude of the waves represent the
light power in the respective beam. The input beam (black, coming in from the left) is split
by the beam-splitter into two beams (up and right) which then move through the interferometer arms, are reflected
by the so-called end mirrors and then recombine at the beam-splitter. This creates in general
to output beams: one travelling to the left and one down. By changing the length of one
interferometer arm the amount of power can be moved between the two output beams.
The sliders can be used to change several parameters of the interferometer:
- Length of second arm – This controls the position of the second mirror
- Reflectivity: beam-splitter – This controls the power reflectivity of the beam-splitter
- Reflectivity: first mirror – This controls the power reflectivity of the first mirror
- Reflectivity: second mirror – This controls thepower reflectivity of the second
In gravitational wave detectors the Michelson interferometer is typically used at the
so-called `dark fringe', i.e. a setup in which no light leaves the interferometer
`downwards'. This can be achieved with a microscopic arm length difference of 0.25 wavelength.
Try to set the Michelson above to the dark fringe yourself.
You can also find out what happens, e.g. to the dark fringe, when you change the reflectvity
of the end mirrors. And of course it's worth investigating the extreme settings just to
see what happens: when you set the beam-slitter reflectivity to 0 or to 1, what do you expect
to see?