When a laser is shone through diffraction gratings, unique patterns can be observed.



When light is shone through an aperture that has a size on or near the same order of magnitude as it wavelength, it will diffract. The diffraction pattern we see emerging is dependent on a few things such as how large the aperture is, its shape, the wavelength of the laser, and the distance from the laser.

Due to Huygens' principle, each point on a wavefront can be considered to be a source. These "secondary sources" as they are known create circular waves, and when combined with other secondary sources, create a mesh of deconstructive and constructive interference that results in the next wavefront.

As a wave coming through the slit diffracts, the point on the wavefront closest to the obstructing edge is a secondary source. The circular waves created from this point do not encounter any interference to one side of them (the obstructed side) and therefore the wavefront created bends in that direction. Since the waves do receive interference from the other side, we see broken lines or dots, separated by areas of deconstructive interference.


  • laser
  • diffraction gratings
  • translucent glass (optional)
  • ring stand with holder for gratings 


  1. Align your laser so that it shoots through your grating and onto translucent glass or another kind of flat surface (such as the wall). 
  2. Experiment with different gratings and observe how the patterns change.

TIP: Turn the lights off for better results.


  • Never shine the laser in or near anyone's eyes. Make sure the laser is well below anyone's eye level when shining through the gratings. 

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