[hamdani yusuf (OP)]

I'm preparing for double wires experiment, but this time the wires have different sizes. I think it's much easier to do than double slits type. They should produce similar results, according to Babinet's principle.

Previous experiment shows that wrinkles on the wires affect the diffraction interference pattern. That's why I ordered needles commonly used to clean up 3D printer nozzles.

[Bored chemist]

The diffraction pattern of light reflected from a cylinder is different to that from light going past an edge.
You might want to paint the wires black.

[hamdani yusuf (OP)]

The diffraction pattern of light reflected from a cylinder is different to that from light going past an edge.
You might want to paint the wires black.

Many DIY single slit experiments I found in YouTube use knife edges made of bare metal.
I've also tried various kind of paints on metal cylinders in my earliest attempt to conduct experiments in diffraction of light, from carbon black to silver, even transparent and fluorescent types. I found no significant difference. I still have the raw footages, but I didn't make the video since I didn't think it was interesting.
I haven't tried some new technology like Vantablack, though. But considering how it works, I don't think it would make much difference. Remember that a borosilicate glass submerged in sunflower oil still produce diffraction pattern, even though they have very similar refractive index which makes it almost invisible.

[hamdani yusuf (OP)]

I haven't tried some new technology like Vantablack, though. But considering how it works, I don't think it would make much difference. Remember that a borosilicate glass submerged in sunflower oil still produce diffraction pattern, even though they have very similar refractive index which makes it almost invisible.

I forgot about the peculiar result in diffraction pattern produced by a single edge made of galvanized steel. It seems like we get interference of light from the core metal and from the coating layer. So I can't predict one way or another until I do the experiment in real life using Vanta black or its equivalent.
I'm curious why there's no mention to musou black in Wikipedia while there are some videos about it in YouTube.

[hamdani yusuf (OP)]

Here's a demonstration of multiple slit diffraction-interference experiment of light.

And here's the picture from an online source.


The slits presumably have the same size, and they are separated by the same distances.

[Bored chemist]

I got bored during lockdown so I decided to measure the wavelength of some light- the green beam from a laser.
It's not that I had any real doubt about it being 532 nm, but I wondered how I could check.
So I looked into thee history of the diffraction grating and discovered this.
https://en.wikipedia.org/wiki/Diffraction_grating#:~:text=The%20first%20man%2Dmade%20diffraction,wire%20diffraction%20grating%20in%201821.

"The first man-made diffraction grating was made around 1785 by Philadelphia inventor David Rittenhouse, who strung hairs between two finely threaded screws"

Fraunhofer did something similar with wires.
I had a go at copying it- after all, I have access to machine-cut screws of pretty good accuracy- and I can check the pitch easily enough.
So I made a grating with a 0.4mm pitch screw and some about 0.2mm coper wire.
Took a while, and it's fiddly as hell.

And it was lousy.
The diffraction pattern was all wrong.

Until I painted it black.
In retrospect I might have done better with black sewing thread.

Later on, I realised I could do better with a grating printed out on an inkjet printer onto OHP slide material.

There's software here.
https://www.coaa.co.uk/software_astronomy.htm

But it was clear that the reflections from the surfaces of the wires really messed up the pattern.

[hamdani yusuf (OP)]

I haven't tried some new technology like Vantablack, though. But considering how it works, I don't think it would make much difference. Remember that a borosilicate glass submerged in sunflower oil still produce diffraction pattern, even though they have very similar refractive index which makes it almost invisible.

I forgot about the peculiar result in diffraction pattern produced by a single edge made of galvanized steel. It seems like we get interference of light from the core metal and from the coating layer. So I can't predict one way or another until I do the experiment in real life using Vanta black or its equivalent.
I'm curious why there's no mention to musou black in Wikipedia while there are some videos about it in YouTube.

This video shows that even the darkest surface is reflective at grazing angle, which is what counts in the case of diffraction.

The World's Blackest Car Is Darker Than Musou Black!
See at 4:40

[hamdani yusuf (OP)]

Fraunhofer did something similar with wires.
I had a go at copying it- after all, I have access to machine-cut screws of pretty good accuracy- and I can check the pitch easily enough.
So I made a grating with a 0.4mm pitch screw and some about 0.2mm coper wire.
Took a while, and it's fiddly as hell.

And it was lousy.
The diffraction pattern was all wrong.

Until I painted it black.
In retrospect I might have done better with black sewing thread.

In my experience, thin copper wire strands tend to wrinkle, especially when they were taken from stranded cables. I think it would be visible under a microscope. I don't think that sewing threads would be much better.


The paint may had straightened out its surface.

My experiments using needles gave better results than thin wires.

[hamdani yusuf (OP)]

Someone else also tried to demonstrate diffraction and interference effect of two edges on the same side.

Here's the short version using knife edges.

This video shows the setup of the 2 Edge Diffraction pattern experiment. The diffraction pattern has more than 100 nodes in the pattern. It uses 2 razor blades held in binder clips and a laser pointer. The razor blades and laser pointer are about 20 feet from the paper displaying the diffraction pattern.

We may argue that the interference pattern shown on the wall is not formed by diffracted lights. They come from the light being scattered by the edge of the razor blades instead. The area on the wall where interference pattern is observed is not located behind the obstacles.

[hamdani yusuf (OP)]

Here's another example of double slit interference using ordinary objects.

The interference pattern indicates that the width of each slits are much smaller than the distance between them. The regularity of fringes' width indicates that the slits have equal width.
But the pattern also shows that they are not perfectly parallel.

[hamdani yusuf (OP)]

I've made the double wires experiment using needles of different sizes.
The first experiment used 0.2 and 0.3 mm needles, while the second experiment used 0.3 and 0.6 mm.
The diffraction-interference pattern are less regularly spaced. The brightness of the fringes are also less periodical.
It supports the hypothesis that the interfering light sources come from the edges instead of the space between them.

[Zer0]

I've been avoiding to post Utube vids...anywayz, here it is...

Thanks & Credits & Source -
Mithuna Yoganathan/Looking Glass Universe(channel)/YouTube.

[hamdani yusuf (OP)]

I've made the double wires experiment using needles of different sizes.
The first experiment used 0.2 and 0.3 mm needles, while the second experiment used 0.3 and 0.6 mm.
The diffraction-interference pattern are less regularly spaced. The brightness of the fringes are also less periodical.
It supports the hypothesis that the interfering light sources come from the edges instead of the space between them.

It's unfortunate that I haven't found enough time to spare to edit, and add narration to the video. I've got tight schedules in the workplace and personal life. But the ideas for other experiments keep coming, which means I'm having a longer backlog.

I don't know which experimental results will convince people that currently common explanation for diffraction of light is erroneous. But I think the more various results against it increases the chance that people will notice.

[hamdani yusuf (OP)]

Just found a video showing refraction of light in aerogel block. Unfortunately, I can't find the video showing experiments of diffraction caused by the edge of aerogel. And I can't find where to buy the aerogel blocks either. I'd like to make a single slit diffraction experiment using two blocks of aerogel.

[hamdani yusuf (OP)]

Here's another type of new material which I'm curious to see the results on diffraction experiments. This mirror made of dielectric material is claimed to be the most reflective mirror in the world, which reflects more than 99.5 percent of visible light.

I also want to know about its penetration depth.

[hamdani yusuf (OP)]

Here's another double slit experiment on YouTube showing a clear interference pattern.

Its shape implies that the slits are much narrower than the distance between them. It also implies that the slits have smooth edges, consistent widths, and parallel to each other. Those are not easy features to achieve. I took them for granted until I tried to make the experiment myself.

[hamdani yusuf (OP)]

Its shape implies that the slits are much narrower than the distance between them.

The pictures below show the different case.

[hamdani yusuf (OP)]

In this video, the distance between the slits seems to be more similar to the width of the slits.

[hamdani yusuf (OP)]

Video showing single slit diffraction of a laser as the slit width is adjusted.  Suitable for A-Level Physics.

Let's focus on a single point in the center of the bright pattern on the screen. When the slit is narrow, this spot becomes much dimmer compared to when the slit is wider, even though the ray of light can still go directly from the light source to that specific spot on the screen.

It could mean that the opaque materials that the single slit apparatus is made of have blocked some of the light that initially would go to that central spot.
Or the edges of the slit have deflected the ray of light hitting them to the central spot, and produce partially destructive interference with the direct ray of light to that spot.
Or a combination of both.

Is there a way to determine which case is the most correct interpretation?

[Origin]

On all of these questions you ask, have you ever gotten an answer that you accepted?  My guess is no.  I'll have just assume the answer is no since this thread is now on ignore.