http://www.ck12.org Chapter 15. Diffraction and Interference of Light
15.3 Diffraction Gratings
- Understand the structure of a diffraction grating.
- Explain the interference pattern formed by diffraction gratings.
- Use diffraction grating interference patterns to calculate the wavelength of light.
Suppose we had a light bulb that emitted exactly four frequencies of light; one frequency in each of the colors red,
yellow, green, and blue. To our eye, this bulb would appear white because the combination of those four colors
produces white light. If viewed through a diffraction grating, however, each color of light would be visible. The
original white light bulb is visible in the center of the image, and interference causes the light bulb to appear in each
color to the left and the right.
Diffraction Gratings
Diffraction gratingsare composed of a multitude of slits lined up side by side, not unlike a series of double slits
next to each other. They can be made by scratching very fine lines with a diamond point on glass, or by pressing
plastic film on glass gratings so that the scratches are replicated. The clear places between the scratches behave as
slits similar to the slits in a double slit experiment and the gratings form interference patterns in the same general
way that double slits do. With more slits, there are more light waves out of phase with each other, causing more
destructive interference. Compared to the interference pattern of a double slit, the diffraction grating interference
pattern’s colors are spread out further and the dark regions are broader. This allows for more precise wavelength
determination than with double slits. The image below shows the diffraction pattern emanating from a white light