[alancalverd]

I just got an even stronger evidence that diffracted light is produced by the edges of the obstacle, instead of the space between those edges.

Isn't that obvious?
Diffraction = light appearing in the geometric shadow area
No edge = no shadow

[hamdani yusuf (OP)]

I just got an even stronger evidence that diffracted light is produced by the edges of the obstacle, instead of the space between those edges.

Isn't that obvious?
Diffraction = light appearing in the geometric shadow area
No edge = no shadow

Most explanations on single slit experiment portray the diffracted light wavelets to originate from the space between the edges of the obstacle, instead of the edges themselves.

[hamdani yusuf (OP)]

The double beam experiment

A bit of optics fun and a little riddle: two coherent light beams of equal intensity and opposite phase meet up. They interfere destructively in the center, thereby creating a continuous plane of zero EM field (and so of zero intensity). The question is: how can the energy in either beam cross and area of zero intensity? Leave a comment if you want to show off your intellect ;-).
 
The experiment in the last 20 seconds of the video shows the cross section of 2 laser beams that meet up and part again. For the experiment I used a single coherent source (HeNe-laser), because that is the only way this experiment could work. It requires a fairly high degree of coherence. Basically it's just a 50% beam splitter and an adjustable mirror under 45 degrees, that create 2 beams of equal intensity, initially spaced 4mm apart, 1mm in diameter and are under an angle of 0.1 degrees with respect to each other. I moved the camera sensor over a distance of 6 meters and recorded 40 images around the area where the beams were crossing paths.

This may not involve diffraction, but it works with the same superposition principle. It may also explain the thin wire diffraction experiment.

[Bored chemist]

The QM answer is "tunnelling".

[hamdani yusuf (OP)]

The QM answer is "tunnelling".

How does it answer the question?
What is the barrier being tunneled?

[hamdani yusuf (OP)]

The question is: how can the energy in either beam cross and area of zero intensity? Leave a comment if you want to show off your intellect ;-).

Here's a comment from the video.

My intuition might be wrong, but it makes me think of mechanical waves. Energy can still travel through nodes of a string even though they don?t move.

And a reply by the video's author.

That is right, standing wave nodes can pass energy. The confusion starts when you think in terms of "beams" or EM radiation being build up of localized "packages" of energy. What you observe are just wave interference phenomena, nothing more.

I also wrote a comment to the video.

The use of reflecting/transmitting beam splitter causes a phase inversion in one of the resulting two beams (the reflected beam). That's why when they interfere after traveling the same distance, the result is a destruction interference.
You can try to use a polarizing beam splitter such as Wollaston prism, and you'll get no destructive interference.
You can also try to use a diffraction grating, and isolate the beam going to the left and right of the same order. You'll get a constructive interference in the center instead of destructive interference.

[hamdani yusuf (OP)]

I just found an interactive simulation web page for diffraction of light.

https://demonstrations.wolfram.com/MultipleSlitDiffractionPattern/

[hamdani yusuf (OP)]

Here are some examples of simulation for double slit experiments.

[hamdani yusuf (OP)]

The simulation is based on the equations below.


The equations are more complex than what's usually taught in school, but they are more general.

[hamdani yusuf (OP)]

Here are some examples of simulation for double slit experiments.

It looks the same as a single slit experiment.

[hamdani yusuf (OP)]

It's obvious that the multiple slit formula isn't general enough to describe the single edge diffraction, or other odd number of edges. Moreover, it doesn't seem to consider the optical characteristics of the material making up the aperture, like opacity, thickness, and polarization state.