Fresnel diffraction patterns can be difficult to see in the classroom. These simulators help students to visualize the effect.

 

• Paul Falstad offers this simulator with selectable aperture shapes

http://www.falstad.com/diffraction/

 

• This simulation from Wolfram illustrates Fresnel diffraction across an edge, with downloadable source code

https://demonstrations.wolfram.com/FresnelDiffractionAtAnEdge/