CH110 Study Guide - Final Guide: Beam Splitter, Plane Wave, Nonlinear Optics
Such experiments can however be explained on a
base of the above undulatory standpoint as well.
When light falls on a beamsplitter, an atom or a
group of atoms (for short, we shall speak of an
atom) in the beamsplitter can come into resonance
interaction with the incident light and thus suck in
an energy portion of En − Em. It should be
emphasized that some atoms of the beamsplitter
do must interact strongly with light as long as the
beamsplitter is not fully transparent. Returning to
the normal state the atom will emit an ordinary
wave train whose intensity will be far above the
intensity of the incident faint light. For this reason
the wave train will be readily absorbed and
reemitted by other atoms of the beamsplitter.
These processes will not permit the train to spread
out. As a result, according to optical laws the train
either will emerge from the beamsplitter in the
direction of Dt or will be reflected towards Dr.
Consequently, the detectors will not give
simultaneous counts. It should be added that an
experimental setup often contains additional
equipment such as different optical plates, filters
etc in which the resonance interaction of the light
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wave with atoms can occur as well. For this
reason too, the input and output light in the setup
may differ drastically, the latter being made up of
intense wave trains going randomly in the
mutually perpendicular directions even if the
former is a continuous plane wave of weak
intensity.
However, as was mentioned in the preceding
section, there are no ideal plane waves in nature
and actual waves are nonuniform, the
nonuniformities being most conspicuous in the
case of a faint light flux. This entails another
mechanism that can explain the results of the
above experiments even if the resonance
interactions are not taken into account. When one
states that there is only one ‘photon’ in an
experimental device, this in fact amounts to saying
that there is a wave train of finite length emitted
by only one atom in the source of light. The wave
train can hit such a site in the half-silvered mirror
of the beamsplitter that will allow the train to pass
almost completely in the direction of Dt. On the
other hand, the wave train can hit a site where the
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