Michelson interferometer
One beamsplitter, two mirror arms, one recombined output — the interferometer behind the Michelson–Morley experiment and, scaled up four kilometers, LIGO.
Open in the canvas →Background
A beamsplitter divides an incoming beam into two arms, each terminated by a mirror that reflects it straight back. Both reflected beams retrace their outbound path and recombine at the very same beamsplitter, producing two output beams whose relative intensity depends on the optical path difference between the two arms. Albert Michelson built the first version in 1881 and, with Edward Morley, refined it into the famous 1887 experiment that searched for Earth's motion through the hypothesized luminiferous ether — and found none, a null result that helped motivate special relativity[1].
The same geometry, scaled to 4 km arms and stabilized to a fraction of a proton's width, is what LIGO uses to detect gravitational waves: a passing wave stretches one arm and compresses the other by an almost unimaginably small amount, which shows up as a shift in the recombined interference pattern[2]. At the tabletop scale, the same layout is a standard tool for measuring small displacements, testing optical flats, and — with a scanning mirror — for Fourier-transform spectroscopy.
What this setup demonstrates
This example places one laser, one beamsplitter, and two mirrors in exactly the Michelson topology: the beam splits at the beamsplitter, each half reflects off its own mirror, and both return to recombine at the same beamsplitter into two output directions, each read by a detector. Every reflection and split follows the same exact vector geometry used throughout OpticalSetup — moving either mirror changes the traced ray paths precisely, the way moving a real mirror would.
This particular scene keeps a line source and a scalar photodetector, so it remains a geometry lesson rather than an interferometric readout. OpticalSetup's bounded coherent model is limited to sized monochromatic CW beams. Switching the source to beam mode can expose supported flat-mirror/beamsplitter path interference, but the app still does not model diffraction, surface figure, vibration, coherence length, or a laboratory detector response.
Related components
References
- Michelson & Morley, "On the Relative Motion of the Earth and the Luminiferous Ether," American Journal of Science (1887)
- LIGO Scientific Collaboration — how LIGO works