[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.

[hamdani yusuf (OP)]

How are holograms possible? | Optics puzzles 5

3d scenes on 2d film, and a diffraction lesson along the way.

Slight correction: In the end, I referenced treating |R^2| as "some real number", so that it's only scaling O. This only makes sense to do because the amplitude of R is constant, or at least it varies only very slowly around a point. In this way, what I say a few moments later about making no assumptions about R is not quite right, we do assume it's a wave with relatively constant magnitude across the film.

[hamdani yusuf (OP)]

I'm making a new video to investigate diffraction of light. Here's a sneak peek.



The lines are drawn to mark the position of dark fringes in each diffraction-interference pattern.

This is the same picture without the marking lines.

In single slit diffraction-interference pattern, the central bright fringe is approximately twice as wide as the other bright fringes. Note that the slit has two edges facing at opposite direction.

In double slit diffraction-interference pattern, the central bright fringe is approximately just as wide as the other bright fringes. Note that the slit has four edges facing at the opposite direction from adjacent edges.

In the same side double edge diffraction-interference pattern, the central bright fringe is approximately three times as wide as the other bright fringes. Note that the fringes on the left side are slightly wider than those on the right side. That's because the position of the camera was on the left of the central spot.

[hamdani yusuf (OP)]

In the same side double edge diffraction-interference pattern, the central bright fringe is approximately three times as wide as the other bright fringes. Note that the fringes on the left side are slightly wider than those on the right side. That's because the position of the camera was on the left of the central spot.

If you follow this thread closely, you might recognize that same side double edge diffraction produces a half interference pattern. Half of the screen shows bright and dark fringes, while the other half, ie. behind the opaque plates, shows only bright line.
So if you wonder how I produced the triple width central bright spot with bright and dark fringes on both sides, it's by using a transparent material for the front plate. Here the back plate was just a metal strip.

[hamdani yusuf (OP)]

These pictures are sneak peek to my next video.

[hamdani yusuf (OP)]

Here you are.

Diffraction of Light 27: Same side diffraction-full-interference pattern

School physics only teach a limited variations of diffraction-interference patterns. In this thread I tried to demonstrate some of uncovered variations, which can show the lack of generality in the mathematical models commonly used to explain the phenomenon.

[alancalverd]

Do you have an example that can't be analysed by Huygens and he usual superposition equations?  Excluding, of course, your hybrid diffraction-reflection-refraction pattern from a thick transparent "edge", or diffraction of a polychromatic beam.

[hamdani yusuf (OP)]

Do you have an example that can't be analysed by Huygens and he usual superposition equations?  Excluding, of course, your hybrid diffraction-reflection-refraction pattern from a thick transparent "edge", or diffraction of a polychromatic beam.

How do you analyze the previous same side diffraction-interference pattern? Can you do it using wavelets based on Huygens' principle?

[alancalverd]

How do you analyze the previous same side diffraction-interference pattern? Can you do it using wavelets based on Huygens' principle?

I could, because I know light travels away from the source, but someone  masquerading as yourself on another topic, seems to think otherwise.

[hamdani yusuf (OP)]

How do you analyze the previous same side diffraction-interference pattern? Can you do it using wavelets based on Huygens' principle?

I could, because I know light travels away from the source, but someone  masquerading as yourself on another topic, seems to think otherwise.

How would you explain these two cases using the same mathematical model for diffraction?