Young’s Double Slit


The experiment named for Thomas Young’s classic proof of the wave theory of light in 1803. While Young’s original experiment used sunlight and calculated the average wavelength to be 550nm, today using monochromatic and coherent light one can calculate wavelength with the following formula:

nλ = xd/L


λ is the wavelength of the light
d is the separation of the slits
n is the order of maximum observed ( for first order n=1)
x is the distance between the bands of light and the central maximum
L is the distance from the slits to the screen center point.

Young’s Double Slits are manufactured by the Lenox Laser Corporation’s proprietary technology that gives a very sharp edge to every slit that makes the geometries and areas of each slit equal (within specifications). This guarantees a very high contrast of diffraction patterns and low flux variations through each of the slits providing good metrology.

In application, these slits may be used to demonstrate Young’s Interference Fringes, Michelson’s Stellar Interferometer (for measuring the separation between double stars) or other applications requiring measurement of the separation between point sources. Go to the Young’s Double Slit Page to activate an interactive applet that will show Young interferences resulting from the interaction of a certain number of waves.

For more information call 1-800-49HOLES or 410-592-3106 or email

Introduction to Young’s Double-slit Experiment

The double slit experiment, thought to have been first performed by English scientist Thomas Young circa 1800, generally refers to an experiment in which light is allowed to diffract through slits which produces fringes, or wave-like interference patterns on an opposing screen.

A similar experiment was performed by Claus Jonsson of the University of Tubingen where beams of electrons showed similar interference patterns. The results of this experiment are often taken as evidence of the “wave-particle duality” predicted by quantum physics. (a.k.a. Englert-Greenberger duality)

In the case two pinholes are used instead of slits, as in the original Young’s experiment, hyperbolic fringes are observed. This is because the difference in paths traveled by the light from the two sources is a constant for a fringe which is the property of a hyperbola. If the two sources are placed on a line perpendicular to the screen, the shape of the interference fringes is circular as the individual paths traveled by light from the two sources are always equal for a given fringe.

It is little wonder that the experiment performed by Dr. Jonsson (Young’s Double Slit applied to the interference of single electrons) ranks first in the list of the top ten most beautiful experiments as chosen by the readers of Physics World magazine.

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