Figure: Diffraction pattern generated by two in-phase point sources

Image 1 Caption: A simulated generic diffraction pattern for two point sources of waves that are emitting in phase. The original caption does not specify the nature of the waves nor whether the simulation is for a 2 dimensional case or 3 dimenional case seen in cross section.

Further explication:

1. The bright and dark bands are the constructive interference fringes which are high intensity regions

2. The fuzzy bands are the destructive interference fringes which are low intensity regions.

3. There is a continuum between high and low intensity regions.

4. The circles emission by the point sources wave pattern with interference turned off. Their intersections coincide with the bright regions.

5. Destructive interference fringes are often called dark interference fringes and constructive ones bright interference fringes, but in Image 1 colors makes the constructive fringes bright and dark and the destructive fringes fuzzy for image clarity. The constructive fringes bright and dark fringes are where the amplitudes add up, respectively, to positive and negative, but the intensity is an absolute value, and so is always positive.

   

6. Image 2 Caption: In Image 2, we see two real cases of two in-phase point sources of water waves. The cases are 2 dimensional. The cases are produced in a ripple tank. Ripple tanks were once common high school physics demonstration equipment.

7. The left-hand case, strongly resembles the simulation in Image 1.

8. The right-hand case, less strongly resembles the simulation in Image 1 because of weaker interference. The most noticeable interference is the fuzzy bands between the sources. The reason for weaker interference is that the point sources are farther apart. Interference is strongest where both sets of waves are strong. But when sources are farther apart, close to a source its waves tend to dominate and farther from both sources, the waves from both sources are weaker. So there is overall weaker interference.

9. The real system is not exactly like the simulation which takes place in an infinite space unperturbed, except the waves directly from the sources. In ripple tanks, the waves will reflect of the sides the tank to some degree and create complicating small effects.

   

10. Image 3 Caption: In Image 3, we see water wave interference resulting from throwing two lumps of ice into a lake simultaneously. The diffraction pattern is qualitatively similar to when you have continuous generation of waves, but the destructive interference is not obvious and the diffraction pattern is transient. The lake is Bachsee in Grindelwald, Switzerland.

    Credit and/or file tracking information follows to the divider line:

    Images:

    1. Credit/Permission: © Dr. Schorsch (AKA User:Xorx), 2005 / CC BY-SA 3.0.
       Image link: Wikimedia Commons: File:Interferenz.jpg.
       
    2. Credit/Permission: Walter Andrew Shewhard 1914 (uploaded to Wikimedia Commons by User:Fae, 2014) / assumed Public domain.
       Image link: Wikimedia Commons: File:A study of the propagation, refraction, reflection, interference and diffraction of ripple waves (1914) (14596074950).jpg.
       
    3. Credit/Permission: © Markus Poessel 2024 / CC BY-SA 4.0.
       Image link: Wikimedia Commons: File:Interfering surface waves on a lake.jpg.
       

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    Stand-alone figure: Optics file: diffraction_two_point_sources_3.html.
    File: Optics file: diffraction_two_point_sources.html.
    

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