The waves that bend around behind the object create a bright line where the shadow would ordinarily begin, but waves that bounce back into the path of the light overlap waves from the source, creating an interference pattern of light and dark bands around the edge of the object (see Figure 2). When light waves originating from a distant point of light strike an opaque object, they tend to bend around the edges, curving both into the shadow and back through the path of other light waves from the same source. Diffraction is a phenomenon similar to dispersion, but is not related to a variation in the wavelength of light.īright bands that are often seen inside the edges of geometric shadows are the result of diffraction. The bars diffract the laser light into widely spaced periodic beams of bright light that can be observed in the figure.
Diffraction series#
An example of light diffraction is presented in Figure 1 for coherent red laser light passing through a very tiny line grating composed of a series of bars on a glass microscope slide. The light that passes through the opening is partially redirected due to an interaction with the edges. This phenomenon is known as diffraction of the light, and occurs when a light wave passes very close to the edge of an object or through a tiny opening, such as a slit or aperture. However, on a much smaller scale, when light waves pass near a barrier, they tend to bend around that barrier and spread at oblique angles. On a large scale, this hypothesis is supported by the seemingly sharp edges of shadows cast by rays from the sun. He explained this observation by describing how particles of light always travel in straight lines, and how objects positioned within the path of light particles would cast a shadow because the particles could not spread out behind the object. In his 1704 treatise on the theory of optical phenomena ( Opticks), Sir Isaac Newton wrote that "light is never known to follow crooked passages nor to bend into the shadow". Molecular Expressions Microscopy Primer: Light and Color - Diffraction of Light
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