PURPOSE: To show white light fringes using a Michelson interferometer.

DESCRIPTION: This experiment uses the laser and white light combination Michelson interferometer setup, which remains set up and aligned and only needs the light source to be installed. The system is pre-aligned according to procedures in the file. Because alignment requires a laser, this demonstration will be delivered (and can be used) with a laser installed. White light from a bright point source is collimated by a condenser lens and passes through a heat filter directly into the interferometer. The light exiting the interferometer is focused onto a distant screen, providing a field about one foot in diameter as shown in the photograph above, clearly visible over the entire lecture hall. The fringe colors can be seen to be negative colors, that is, complementary colors to the colors to the spectral colors which are eliminated by destructive interference.

A neat finale to the experiment is to burn a match, blow it out and stick the hot head into one path of the interferometer, producing heat fringes.

SUGGESTIONS: This setup is sensitive to mirror position; the correct position is written on the micrometer screw adjuster for the moveable mirror. Check that you have it aligned before trying to demonstrate it.

REFERENCES: (PIRA 6D40.10) See Demonstration Reference File for alignment procedure using a laser as well as a large number of articles dealing with thenwhite light Michelson interferometer.

EQUIPMENT: Michelson interferometer, bright white light point source with condenser lens and heat filter, 20 cm imaging lens.

SETUP TIME: 5 min.

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