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Recently i encountered a problem on the Young's Double Slit Experiment. The question was paragraph and had multiple sub-parts on the different variations of the experiment.

One of them was about what would happen to the interference pattern if one of the slits was closed. Initially i thought that the slit will act as a single source and so no pattern will be observed fringes will disappear and there will be a uniform illumination over a part of screen. It was indeed the right answer and I really didn't put much thought into it.

Later on one of my friends posed another possibility that why the single slit will not show diffraction patterns.

I think the main reason for this is because in diffraction the size of slit is quite wide as compared to YDSE and so it shows the multi-source interference diffraction pattern. But the reasoning is quite vague and not satisfactory.

So, my question is WHAT ARE THE POSSIBLE REASONS FOR SLIT TO NOT SHOW DIFFRACTION PATTERN

NOTE: All the situations and conditions shall be assumed ideal and not a much complicated practical system. Source shall be considered monochromatic.

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  • $\begingroup$ Light passing through a slit will always exhibit diffraction. It's a property of physics. Are you asking about the visibility of the pattern? $\endgroup$
    – Vincent Thacker
    Commented May 2 at 17:30
  • $\begingroup$ @vincentthacker yeah $\endgroup$
    – Yash Shrivastava
    Commented May 2 at 17:34
  • $\begingroup$ see physics.stackexchange.com/questions/799741/… $\endgroup$
    – hyportnex
    Commented May 2 at 20:32
  • $\begingroup$ @hyportnex doesn't this means that in my case the diffraction pattern should be more clear? $\endgroup$
    – Yash Shrivastava
    Commented May 3 at 5:04
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    $\begingroup$ It is more of a dynamic range issue: all detectors have a natural dynamic range that is the ratio of maximum/minimum. A bright background can saturate your eyes even when it is not on the same but just on nearby pixels, and this is what a large hole does. It makes you see the large bright patch next to the much dimmer diffraction induced ripples that is near the edge of the hole. By smoothly attenuating the transition between the hole and the opaque obstacle, "sidelobe tapering" to antenna engineers or "apodizing" to opticians, you can get rid of the ripples completely. $\endgroup$
    – hyportnex
    Commented May 3 at 16:08

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It is more of a dynamic range issue: all detectors have a natural working dynamic range that is the ratio of the maximum detectable intensity to that of the minimum. A bright background can saturate your eyes even when it is not on the same but just on nearby pixels, and this is what a large hole does. It makes you see the large bright patch next to the much dimmer diffraction induced ripples that is near the edge of the hole. By smoothly attenuating the transition between the hole and the opaque obstacle, a process called "sidelobe tapering" by antenna engineers and "apodizing" by opticians, you can get rid of the ripples completely. Of course, this assumes that you have a hole with the partially transparent tapering is at least a few wavelengths across.

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