Diffraction intensity at a slit and at a wire - Babinet's theorem

Principle

An aperture consisting of a single slit and a complementary strip (wire) is illuminated with a laser beam. The corresponding diffraction patterns are measured according to position and intensity with a photocell which can be shifted.

Benefits

• surprisingly a slit and a wire show basically the same diffraction pattern
• measurements prove a theorem that sounds awkward at first glance
• sturdy setup allows good reproducability of results

Tasks

1. Determination of the intensity distribution of the diffraction patterns due to a slit and complementary strip (wire).
2. Determination of the intensity relations of the diffraction pattern peaks for the single slit.
3. Babinet's theorem is discussed using the diffraction patterns of the slit and the complementary strip.

Learning objectives

• Huygens' principle
• Interference
• Fraunhofer und Fresnel diffraction
• Babinet's theorem
• Poissons' spot
• Coherence
• Laser