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caused by a bird feather, which was effectively the first diffraction grating. In 1803
Thomas Young did his famous experiment observing interference from two
closely spaced slits. Explaining his results by interference of the waves emanating from
the two different slits, he deduced that light must propagate as waves. AugustinJean Fresnel did more definitive studies and calculations of diffraction,
published in 1815 and 1818, and thereby gave great support to the wave theory of light
that had been advanced by Christiaan Huygens and reinvigorated by
Young, against Newton's particle theory.
Thomas young sketch that was presented to
the royal society in 1803.
Diffraction arises because of the way in which waves propagate; this is described by the
Huygens–Fresnel principle. The propagation of a wave can be visualized by considering
every point on a wavefront as a point source for a secondary radial wave. The
subsequent propagation and addition of all these radial waves form the new wavefront.
When waves are added together, their sum is determined by the relative phases as well
as the amplitudes of the individual waves, an effect which is often known as wave
interference. The summed amplitude of the waves can have any value between zero
and the sum of the individual amplitudes. Hence, diffraction patterns usually have a
series of maxima and minima.
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