This may seem like a simple question, but I cant seem to make any headway.
Consider the following; I have two beams of light, a reference beam $(A=\cos(wt))$ and phase shifted beam $(B=\cos(wt+\phi))$.
What is the normal way (say in a lab) that $\phi$ is detected & measured with respect to the reference beam?
I believe an interferometer is used, but I dont understand how this yields a measurement.
Thanks for any insight.
EDIT: I don't know if I've explained this very well. I think better in pictures, so here is a VERY crude diagram of my thought experiment.