Diffraction intensity of multiple slits and grids

Principle

Multiple slits which all have the same width and the same distance among each other, as well as transmission grids with different grid constants, are submitted to laser light. The corresponding diffraction patterns are measured according to their position and intensity, by means of a photo diode which can be shifted.

Benefits

• Understand what makes an optical grid work, by approaching it via "multiple slits"
• The coherent light of a laser gives the possibility of easy observation
• Clear correlation of measurement results to the underlying theory

Tasks

1. The position of the first intensity minimum due to a single slit is determined, and the value is used to calculate the width of the slit.
2. The intensity distribution of the diffraction patterns of a threefold, fourfold and even a fivefold slit, where the slits all have the same widths and the same distance among each other, is to be determined. The intensity relations of the central peaks are to be assessed.
3. For transmission grids with different lattice constants, the position of the peaks of several orders of diffraction is to be determined, and the found value used to calculate the wavelength of the laser light.

Learning objectives

• Law of Huygens principle
• Law of Interference
• Law of Fraunhofer and Fresnel diffraction
• Law of Coherence
• Law of Laser