Video Transcript
The diagram shows some apparatus
used in holography, including a cylindrical object. Which of the labeled components is
a beam splitter?
We must identify the beam splitter
in the diagram. First, let’s see that the diagram
corresponds to a configuration of an apparatus that is used to record a holographic
image of a cylinder. We can see that component I is the
coherent light source, such as a laser. A beam of this coherent light
travels from the light source and is then incident on component II. We can see that two beams travel
from component II. One beam travels to component III,
and one beam travels to component IV.
We can see that for both component
III and component IV, one beam travels to them and one beam travels from them. For both component III and
component IV, there is an angle between the beam traveling to the component and the
beam traveling from the component. The angles between each of these
beams and the normal to the surface of the component are equal. This means that component III and
component IV are mirrors. These components are therefore not
beam splitters.
Unlike components III and IV,
component V and component VI appear to have two beams traveling from them and only
one beam traveling to them. However, the beams apparently
traveling from components V and VI are actually the edges of a single diverging
beam. We can see this for component
VI. A component that converts a planar
beam into a divergent beam is a divergent lens. Components V and VI are concave in
shape. So it makes sense that they are
diverging lenses. These components are therefore not
beam splitters.
Now then, component VII has the
divergent beams from components V and VI incident on it. No beams travel from it. Component VII is where a
holographic image is recorded. So, if the function of component
VII is to record a holographic image, what is the function of component II?
Component II has the function of
separating the beam from the light source into two beams, or said another way it
splits a beam of light into two beams. This is why this component is
called a beam splitter. So the component that is a beam
splitter is the component labeled II.
