Diffraction from a Straight Edge
Safety Warnings
Danger: Class 3B Laser Hazard
Warning: Electrical Safety
Purpose
An expanded He-Ne laser beam illuminates various objects on a rotating disk — razor blade, needle, pin, pinhole, and wire — to produce Fresnel diffraction patterns on a screen. Students observe how light bends around obstacles and into geometric shadow regions, demonstrating the wave nature of light.
Figure 1:
Straight edge (razor blade) diffraction pattern showing Fresnel fringes along the shadow boundary.
Figure 2:
Complete setup on the optical breadboard cart: He-Ne laser with spatial filter, negative lens for beam expansion, and rotating disk holding the diffraction objects.
Figure 3:
Diffraction pattern from the needle, showing the dark geometric shadow surrounded by curved Fresnel fringes.
Figure 4:
Diffraction pattern from the straight pin, showing fringes around both the shaft and pin head.
Figure 5:
Diffraction pattern from the wire, showing periodic vertical fringes with light penetrating into the shadow region.
Figure 6:
Diffraction pattern from the pinhole aperture, showing concentric Airy rings.
Figure 7:
The rotating disk with six positions: razor blade, needle, straight pin, pinhole, wire, and an empty opening for undisturbed beam reference.