Suppose a laser is split into two coherent beams and these beams are then superi

Question

Suppose a laser is split into two coherent beams and these beams are then superimposed such that they intersect in an infinite ray to form a new light beam which is the combination of the two. Now suppose one of the two beams is made to be perfectly out of phase with the other; should I expect the beam which is the combination of the two to disappear since the two light beams that make it up will always destructively interfere? If so, how does the conservation of energy work in this case? Moreover, what does this "beam" interact with? For example, suppose there are two beams of light that perfectly destructively interfere for a distance of the diameter of an atom, and one places an atom at such a destructive point -- will the light beam pass straight through?

Explanation / Answer

There's a tricky assumption hidden in your phrase "these beams are then superimposed such that they intersect in an infinite ray to form a new light beam ". How would that process work? If you try merging the beams at a small angle, then across the width they will alternate between constructive and destructive interference. The way they can really be merged is with a beam-splitter, where one is partially transmitted and the other partially reflected. Then you get two combined beams, going in different directions. If the phase is adjusted to eliminate one beam the other one gets all the energy
If you take some interference pattern with nodes, it's true that any molecule at a node won't absorb any energy. This sort of thing is done routinely in various experiments.

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