Arago’s Spot, also know as Fresnel bright spot, or Poisson spot, is a bright point that appears at the center of a circular object’s shadow due to Fresnel diffraction.
Set up: Laser -22mm lens about 5 cm from laser, .7 cm ball 40-60 cm from lens, screen about 3 meters from ball. Use a camera to show a whole class or have a bright He-Ne and a long throw. 🙂
Location, Glass plate with ball: J3-5, Laser: P1-4, Lens and mount: Optics cart