Diffraction And Interference

 

The phenomena of diffraction occurs for all waves.  The most common examples are water waves bending around a fixed object or light around the edge of an object - the shadow edge is never well defined.  The animation to the right demonstrates a wave front passing through two small openings. It visibly changes direction, or diffracts, as it passes through the opening.  The phenomena of interference can also be seen.

Commercial diffraction gratings consist of many closely spaced parallel grooves that will separate white light into it’s component colors, just as a prism does.  A common example is the surface of a DVD. The image to the right illustrates the pattern of dots on the surfaces of a CD and DVD.  The width of a dot for the DVD is about 400 nanometers.


Interference is the phenomena of two waves meeting and adding together to form a resulting wave that is the sum of the amplitudes of each wave at the point of overlap.  The lower graphic shows the resulting waveform (on top) for two waves in phase and out of phase.  The colors in the soap bubble to the right are due to the interference of light reflecting off the front and back surfaces of the bubble. Since the bubble thickness varies, different wavelengths (colors) will interfere constructively and destructively and produce the rainbow of colors.