Higher order spectra from a diffraction grating

Higher order spectra from a diffraction grating

We have seen that reinforcement occurs for light diffracted from adjacent slits in a diffraction grating at an angle 8 given by, Reinforcement will also occur when the angle of diffraction is such that the path difference for light from adjacent slits is 2}” 32, and so on. We therefore may obtain diffracted images for any particular wavelength at larger angles given by,

1

These are called the second and third order images respectively. The actual number of orders possible for any particular colour will depend on the width of the grating space. Sin 8 cannot be greater than I (900 diffraction), so that the maximum number. Two orders of spectra can be seen using the plastic replica described earlier in this chapter. Coarse gratings with a wide spacing give several orders as may readily be
seen if a diffraction experiment is performed using a piece of fine wire gauze.

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