When Michelson and Morley conducted their 1887 interferometer experiment, they were expecting a fringe pattern shift of 0.4 (see the chart at http://en.wikipedia.org/wiki/Michelson-Morley_experiment). I understand that fringe patterns are represented as series of alternating dark and light bands, but I don't understand what exactly one fringe is. In particular, would a fringe shift of 1.0 be defined as a dark band moving (shifting) to where its adjacent dark band had previously been?
To check my understanding:
- If so, then if a laser with a 532 nanometer wavelength were used as the light source in a Michelson-Morley style interferometer, would adjusting the position of the movable mirror a total of 266 nanometers (266 rather than 532 because the beam reflects back off the mirror) result in a 1.0 fringe shift as previously defined?
- Or, since light waves are sinusoidal, would the dark bands occur at every crossing of the x-axis (and the light bands at the peaks and valleys), such that the 1.0 fringe shift would occur after moving the mirror only 133 nanometers - rather than the 266 nanometers of the previous question?