In this case, the lasers can be used to measure very small distances over a range of many miles. This is accomplished by splitting the laser beam and reflecting it back from different surfaces. In reflection holograms, both a reference and object-illuminating beam are reflected onto a thick film from opposite sides. These beams interfere to produce light and dark areas that correspond to an image that appears three-dimensional. Transmission holograms use both the reference and object-illuminating beams on the same side of the film to produce a similar type of effect.
Interference also occurs with sound waves and waves induced in a standing pool of water.
A very concise and easy interference experiment can be performed at home using a sink full of water and two marbles. Just as with light waves, the two marbles will induce a series of waves in the water emanating in all directions. Waves formed in the area between where the marbles entered the water will eventually collide. Where they collide in step, they will constructively add together to make a bigger wave and where they collide out of step they will destructively cancel each other out. Authors Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.