You can use "low-coherence interferometry" to measure tiny signals that would be undetectable otherwise. Combine a "reference" beam with a "signal" beam and you get a measurable interference pattern, even when the magnitude of the signal beam is miniscule.
This is what a real-life interference pattern looks like (I just acquired this from an actual interferometer illuminating a painted metal surface):
This is now an established medical imaging method (Optical Coherence Tomography) to create 3d scans of biological tissue. It can also be used to measure distance or elevation changes on a surface of anything from a micrometer-level scale to a planetary surface. All you need is to use light with the right wavelengths and two measurements "arms" of roughly the same length.
You can use "low-coherence interferometry" to measure tiny signals that would be undetectable otherwise. Combine a "reference" beam with a "signal" beam and you get a measurable interference pattern, even when the magnitude of the signal beam is miniscule.
This is what a real-life interference pattern looks like (I just acquired this from an actual interferometer illuminating a painted metal surface):
https://dl.dropboxusercontent.com/u/30682604/fringe_signal.p...
This is now an established medical imaging method (Optical Coherence Tomography) to create 3d scans of biological tissue. It can also be used to measure distance or elevation changes on a surface of anything from a micrometer-level scale to a planetary surface. All you need is to use light with the right wavelengths and two measurements "arms" of roughly the same length.