Index Key:  PHY092
Author:     kolin
Subject:    How do holograms work?

Response #:  1 of 1
Author:      Arthur Smith
Text:        Most of the time we can ignore the wave nature of light, since it 
basically travels in straight lines and obeys simple laws when passing through 
lenses or with mirrors.  However, when light is specially prepared (as in a 
laser) the wave nature can be readily seen - for example, laser light passed 
through a pair of slits will produce an "interference" pattern of alternating 
dark and light areas as long as the slits are close enough together, and this 
is very different from the straight line images you might expect.  A hologram 
is made by "interfering" in this sort of fashion, laser light that has been 
reflected from a 3-dimensional object with light directly from the laser, or 
reflected from a flat mirror.  Because of the different distances traveled by 
the light striking different parts of the object, the light waves arrive at 
different parts of their cycle and combine or cancel out.  This produces a 
very complicated image, which can be recorded on film as a hologram, and 
played back to produce something resembling the original 3-dimensional image 
(played back by shining laser light through it in the other direction).  The 
details are pretty complicated, and I have always been amazed that it actually 
works.  People can now produce these interference patterns on the computer, 
and generate a hologram that can be used to produce three-- dimensional images 
that were designed on the computer.