Double Slit Diffraction

Laser diffraction compared to intensity diagrams

The pattern formed by the interference and diffraction of coherent light is distinctly different for a single and double slit. The single slit intensity envelope is shown by the dashed line and that of the double slit for a particular wavelength and slit width is shown by the solid line. The photographs of the single and double slit patterns produced by a helium-neon laser show the qualitative differences between the patterns produced. You can see that the drawing is not to the same scale as the photographs, but the breaking up of the broad maxima of the single slit pattern into more closely spaced maxima is evident. The number of bright maxima within the central maximum of the single-slit pattern is influenced by the width of the slit and the separation of the double slits.