# How Small a Slit can Light Pass through?

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?

• en.wikipedia.org/wiki/Near-field_scanning_optical_microscope Commented Nov 20, 2020 at 16:04
• @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".
– JEB
Commented Nov 20, 2020 at 16:54
• 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? Commented Nov 21, 2020 at 7:29
• With quantum tunneling some photons will always go through. Commented Nov 21, 2020 at 9:08
• The theory for narrow openings is basically the same as for Rayleigh scattering: the transmission goes down with the fourth order of the size to wavelength ratio. I don't know if long slits scale that way (I assume they do), but small holes do. Commented May 14, 2023 at 17:25

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.

• Really nice answer. Commented Nov 21, 2020 at 17:36