A helium-neon laser of power mW at nm feeds a Michelson interferometer
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Photodetection, photonic sources and quantum optics · Photodetection, photonic sources and quantum optics
Optics and Photonics, Ch The photon
Problem
A helium-neon laser of power P=1.0 mW at λ=633 nm feeds a Michelson interferometer. Its beamsplitter divides the incident power equally between the two arms (Chapter 10); one arm ends in a fixed mirror, the other in a fully reflecting mirror mounted on a sensitive force balance. Assume no other losses.
((a)) Find the photon flux entering the interferometer.
((b)) Find the force exerted on the movable mirror by the light in its own arm, assuming the mirror reflects that light straight back the way it came.
((c)) The laser is then attenuated by a factor of 1012, so that far fewer than one photon is inside the interferometer at any instant, and the mirror is scanned through 5 fringes of visibility V=0.95. Taking well above the counting noise to mean at least 50/V2 photons entering the interferometer during each fringe, estimate the minimum observing time for the fringes to emerge.