If you imagine light source passing through a single slit of variable thickness, as you lower the thickness of the slit the light will diffract more and more until the slit is small enough that no light is passing through.

Is the minimum size of the slit through which light can successfully pass the amplitude of the light wave? If this is true, what happens when the slit is just slightly too small for the light?

Basically, what is the smallest slit through which light can pass and what happens when the slit is just slightly smaller than that?

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    $\begingroup$ en.wikipedia.org/wiki/Near-field_scanning_optical_microscope $\endgroup$ – Jon Custer Nov 20 '20 at 16:04
  • $\begingroup$ @JonCuster doesn't "near field" mean (loosely): "non-radiative"? It's unclear whether the question is regarding $1/r^2$ radiation traversing a slit, or just "field". $\endgroup$ – JEB Nov 20 '20 at 16:54
  • $\begingroup$ Good question, I asked a similar question where I considered the light to be polarized perpendicular to the slit and assumed no photons could make it through. Then I wondered if you slowly opened the slit at what width would photons begin to go through? $\endgroup$ – Bill Alsept Nov 21 '20 at 7:29
  • $\begingroup$ With quantum tunneling some photons will always go through. $\endgroup$ – Andrew Nov 21 '20 at 9:08

The wavelength is important in describing the diffraction patterns, but as classical electromagnetic waves are an emergent phenomenon from zillions of photons, I would guess that the limit would be when the distances between atoms are reached.

In this link there is a description of a double slit experiment at the nano scale:

In their study, Zia and Brongersma created a slightly different version of Young’s original experiment. Two gold stripes protruding on a 48-nm-thick gold film, which served as waveguides for the SPPs, played the role of the traditional two slits. The stripes’ dimensions—each 2 micrometers thick and separated by a gap of 2 micrometers—were important because, as waveguides, they support only the lowest-order SPP mode


Zia and Brongersma’s results closely resembled the interference pattern of Young’s double-slit experiment. Like macroscopic light waves,

So there is research going on , bringing the distances to nanoscale.

  • $\begingroup$ Really nice answer. $\endgroup$ – Árpád Szendrei Nov 21 '20 at 17:36

The thing is, it depends on the wavelength and frequency of the light. If you are talking about the visible spectrum, the smallest the slit can be is 380 nanometers that is, very blue-shifted. If the slit is smaller than that, there will be a "shadow" i.e. absence of light (darkness). If you still want light to pass through that, then you can increase the frequency (by adding more energy, you decrease the wavelength) of the electro-magnetic radiation (basically its just light). Then you can go smaller like x-rays (10 nm) and even smaller like gamma-rays and even smaller like hard gamma-rays (1 × 10^-9 nm). The smallest you can scientifically make the radiation be is a Planck length. Meaning that the slit should be as small as a Planck length! That is REALLY small (approx. 6.6260693(11) * 10^-34). Any smaller than that and you'll break space-time.

Thanks for your time! Please correct me if I'm wrong. I did my research but I am still human :) (Newcomer here!)

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    $\begingroup$ As noted in the comment under the question, sub-wavelength optics are a thing. $\endgroup$ – Jon Custer Nov 20 '20 at 16:18
  • $\begingroup$ Does it depend only on the wavelength or also the frequency? $\endgroup$ – Archisman Panigrahi Nov 20 '20 at 16:20
  • $\begingroup$ @ArchismanPanigrahi Wavelength and frequency are completely related considering the speed of light $\endgroup$ – Bill Alsept Nov 21 '20 at 7:19
  • $\begingroup$ @BillAlsept Suppose I put the system inside water. My intuition says that the slit width would depend on the wavelength (with the same relation they had in air), and not on the frequency. $\endgroup$ – Archisman Panigrahi Nov 21 '20 at 7:48
  • $\begingroup$ @ArchismanPanigrahi I’m just saying it has everything to do with frequency. For instants a photon with a 500nm wavelength actually has a frequency of over 600 trillion oscillations per second. As it propagates along at the speed of light it completes one oscillation every 500 nanometers. In reality it has nothing to do with waves. $\endgroup$ – Bill Alsept Nov 21 '20 at 8:30

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