The Interferometer

Abstract:

The interferometer is the most accurate measuring device known to man. It was created by Albert A. Michelson. The operation of the interferometer described briefly is a light beam that is separated by a beam splitter. The two beams then travel equal distances at 90° of each other where they are reflected off two mirrors back through the beam splitter. They are then superimposed on to a screen. The screen will display an interference pattern of fringes. The interferometer is extremely sensitive to vibrations and should be isolated from them

The interferometer is the most accurate device presently known to man, and most likely will remain the most accurate measuring device for the next hundred years” Cal Christiansen. The interferometer can measure lengths of one half the wavelength of the light source being used. With a HeNe laser (Helium Neon) this length is 316.4nm, about 1/3 of a micron. The interferometer is able to measure very small distances by the interference produced between two lasers beams. With this degree of accuracy there are clearly many uses for this device including, measuring flatness, structural stress, and making linear measurements.

Albert A. Michelson is the father of the interferometer and the “Michelson Interferometer” is still used today. Michelson was born in Prussia in 1872 and later moved to the United States where he joined the U.S. Navy. As an instructor in the Navy academy he was asked to demonstrate the Foucault method of measuring the speed of light and made several improvements on it. Michelson received a grant and built his first interferometer much like the one presently used. It consisted of an Argand lamp, two mirrors, two beam splitters and an eyepiece. The device was extremely sensitive to vibrations and wasn’t accurate until it was brought to the Potsdam Astrophysical Observatory in Berlin where it was mounted on a platform designed for an equatorial telescope. With proper setup Michelson attempted to detect the presence ether, an invisible undetectable material that surrounded by all matter. This was unsuccessful and Einstein later declared that the ether did not exit and light travels at the same speed in all directions. Michelson would later receive the Nobel Prize for science for “precision optical instruments and the spectroscope and metrological investigations conducted herewith.” Several versions of the interferometer were devised by Michelson including, the interferential comparator for standardizing the meter, a mechanical harmonic analyzer for testing the harmonic motion of fringes, and a stellar interferometer for measuring the size of stars.