Introduction:
This experiment is aimed to study the generation of Fourier transform of different diffraction
gratings (objects) and then measure the intensities of the frequencies of different orders in the
Fourier plane. The whole process is as under in chronological order.
Generation of collimated beam:
We know that laser beam is not a collimated beam and it diverges as it propagates due to
diffraction. To get a collimated beam, two convex lenses are used. One lens converges the beam
and the other lens then collimates the beam. But this will only happen if the distance between the
two lenses is
D=f1+f2
Where
D= distance between the two lenses
f1= focal length of one lens
and f2= focal length of the second lens
The arrangement is shown diagrammatically as under.
The next task is to get a Fourier transform of a grating.
Generating the Fourier transform:
After getting a collimated beam we put a diffraction grating in front of the beam, and then place
a Fourier transform lens to get a Fourier transform of the grating. The Fourier transform can be
seen on a plane paper (called a Fourier plane). The arrangement is shown as under.
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