In this week’s Fourier Optics course we shall be looking at diffraction from 2D apertures, using Fourier methods. Here is a (Cartesian separable) rectangular aperture, and the corresponding Fraunhofer intensity pattern. - ThreadSky

ifanghughes.bsky.social • 36 days ago

In this week’s Fourier Optics course we shall be looking at diffraction from 2D apertures, using Fourier methods.

Here is a (Cartesian separable) rectangular aperture, and the corresponding Fraunhofer intensity pattern.

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ifanghughes.bsky.social•36 days ago

Many capital letters can be constructed from rectangular apertures, making it easy to calculate the corresponding Fraunhofer intensity pattern.

For example, here is diffraction pattern of E. Vertically we see interference of 3 identical copies of horizontal bars.

ifanghughes.bsky.social•36 days ago

Many optical instruments (microscopes, telescopes, camera lenses) have cylindrical symmetry, and the Airy pattern is the characteristic diffraction pattern of a circular aperture.

ifanghughes.bsky.social•36 days ago

The power of the Fourier technique becomes apparent when calculating the diffraction pattern of identical copies of apertures.
The simplest example is two circles. We see the Airy pattern modulated with cos-squared fringes – interference from the two apertures.

ifanghughes.bsky.social•36 days ago

For three circles we again see an Airy envelope, and the interference pattern now has subsidiary maxima.

ifanghughes.bsky.social•36 days ago

For a three by three array of triangles we see:
(i) Hexagonal shape of diffraction form one triangle
(ii) Vertical fringes with one subsidiary maximum between principal maxima
(iii) Horizontal fringes with one subsidiary maximum between principal maxima

ifanghughes.bsky.social•36 days ago

We also see this in the laboratory! Here are the Fraunhofer diffraction patterns of (i) two and (iii) five slits. There are three subsidiary maxima for the latter. Note the excellent agreement between theory and experiment.

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