Diffraction from Crossed Slits

The diffraction pattern at left is formed by passing the light from a helium-neon laser through short slits which cross at a 90° angle, like a plus sign. The basic geometry is shown below.

This pattern shows that the diffraction pattern reveals the symmetry of the object from which it is diffracted. The 90° angles in the object are shown by 90° angles in the diffraction pattern. The spaces between the bright concentrations of light are inversely proportional to the widths of the slits forming the object, and could be used to measure those widths.

Conceptually, this is similar to using x-ray diffraction to reveal the symmetry and lattice spacings of the atoms in a crystal lattice.

Note: The diffraction pattern was projected upon a piece of graph paper - that accounts for the dark lines. They are not a part of the diffraction.