Diffraction Grating

Key Stage 5

Meaning

A diffraction grating is a plate with many closely ruled parallel slits that disperses white light into a spectrum or produce several diverging beams from a single laser beam.

About Diffraction Gratings

• Diffraction gratings produce multiple diffraction orders for a single monochromatic beam of laser light.
• When white light is incident upon a diffraction grating it will produce a single white band of light in the centre of the screen followed by a series of repeating spectra. As the distance from the centre of the screen increases with violet closest to the centre and red furthest.
• Diffraction Gratings can resolve very fine details in the spectrum, making them useful in spectroscopy.

	This image shows a diffraction grating splitting a red laser beam into a zeroth, first, second and third order beam.
	This image shows a diffraction grating splitting a green laser beam into a zeroth, first, second, third and fourth order beam.
	This image shows a diffraction grating splitting a green laser beam into a zeroth, first, second, third, fourth and fifth order beam.

Formula

The diffraction angle depends on the wavelength of the light and the spacing of the slits with the relation given by this formula:

• \(𝑑sin𝜃=𝑛𝜆\)

Where:

𝑑 is the slit spacing (though frequently the number of slits per mm is given and this must be calculated first)

𝜃 is the angle between the beam order and the central axis

𝑛 is the beam order with the zeroth beam order being along the central axis and the first beam order being smallest angle from beam to central axis

𝜆 is the wavelength of the beam