(1) Laser light takes the picture in holography. There is a mirror behind the
tree which reflects the laser light toward a piece of film. The developed film will have a
record of the light waves which were reflected from the mirror combined with the light
waves that were reflected from the tree.
Figure 2-19. Holograph by laser beam.
(2) The film is called a hologram. When a laser beam hits the film, you will
be able to see a three-dimensional image of the tree on the other side of the film. The
reason you see a three-dimensional image is because you are seeing the same light
reflections you would see if you were looking at the tree itself.
(3) Holograms are used in companies for three-dimensional advertising and
by engineers looking for hidden wear and vibration in moving machine parts. A person
can have a holographic portrait taken, and there is a video game with a three-
Figure 2-20. Holograph.