[hamdani yusuf (OP)]

Why did you think I would plough on through the rest of it?

To avoid embarrassment.

[Bored chemist]

Single edge diffraction of a narrow parallel light beam

What made the beam narrow?

Collimating lens.

That doesn't answer the question.
The beam they bounced off the mirrors on the moon was sent out via a collimating lens (OK strictly a mirror but that makes no difference) 3 metres across.
But the mirrors are only about 1/6 of that size.

What you seem not to realise is that a beam is only "finite" because it has been sent through some aperture.
In the case of a laser pointer, the aperture is inside the laser itself.
But there is always some sort of limit.
So the answer to "What made the beam narrow?" is always " a set of edges".

You think you have an experiment where there's only one diffracting edge.
Are you sure?

Why did you think I would plough on through the rest of it?

To avoid embarrassment.

Whose?
Who will be embarrassed by you posting a video in which you say something that's wrong.

[hamdani yusuf (OP)]

So the answer to "What made the beam narrow?" is always " a set of edges".

Here's a diagram of semiconductor laser.

The width of the gap between the substrates determines the minimum width of the light beam at the focal point of Collimating lens. Without the lens, the light beam would be divergent, thus won't stay narrow for long.

[hamdani yusuf (OP)]

You think you have an experiment where there's only one diffracting edge.
Are you sure?

How many edges do you find in that video?

[hamdani yusuf (OP)]

Whose?
Who will be embarrassed by you posting a video in which you say something that's wrong.

What's the wrong thing I said?
What should be said instead to make it right?

[Bored chemist]

So the answer to "What made the beam narrow?" is always " a set of edges".

Here's a diagram of semiconductor laser.

The width of the gap between the substrates determines the minimum width of the light beam at the focal point of Collimating lens. Without the lens, the light beam would be divergent, thus won't stay narrow for long.

You missed a few relevant bits.

edges.png (43.57 kB . 1085x912 - viewed 1059 times)

[hamdani yusuf (OP)]

You missed a few relevant bits.

After hitting the edges, the laser beam will diverge, until it's made parallel by Collimating lens.

[Bored chemist]

You missed a few relevant bits.

After hitting the edges, the laser beam will diverge, until it's made parallel by Collimating lens.

No

edges.png (52.92 kB . 1085x912 - viewed 1071 times)

[hamdani yusuf (OP)]

You missed a few relevant bits.

After hitting the edges, the laser beam will diverge, until it's made parallel by Collimating lens.

No
 [ Invalid Attachment ]

Where do you think the top and bottom light beam coming out from the lens come from?
What do you think the light beam would look like if the lens is removed?

[Bored chemist]

You missed a few relevant bits.

After hitting the edges, the laser beam will diverge, until it's made parallel by Collimating lens.

No
 [ Invalid Attachment ]

Where do you think the top and bottom light beam coming out from the lens come from?
What do you think the light beam would look like if the lens is removed?

Please try to pay attention.
The edge of the lens will cause diffraction.
So the light coming out of the lens can not possibly all be collimated.

[hamdani yusuf (OP)]

Please try to pay attention.
The edge of the lens will cause diffraction.
So the light coming out of the lens can not possibly all be collimated.

The lens is much larger than the gap between the substrates. The light beam coming to the edges of the lens has near zero intensity. Its contribution to the diffraction and interference pattern in commonly used single slit experiment is negligible.
It seems like you have been misled by a rough sketch. Your attention was driven to focus on some errors in the details, rather than how it was intended to illustrate, which is showing how a semiconductor laser work.

[Bored chemist]

The lens is much larger than the gap between the substrates.

It is finite.
It diffracts.

It seems like you have been misled by a rough sketch.

In what way?

which is showing how a semiconductor laser work.

Do you really think I didn't know?

[alancalverd]

Not sure who is arguing what here, but it's worth noting that unlike a gas laser, the emission from a solid state unit is not inherently parallel, nor is it from a point source. Therefore focussing, either to a point or to a parallel beam, is inherently imprecise.

[hamdani yusuf (OP)]

It is finite.
It diffracts.

The diffraction is produced by the edges of the aperture, rather than the lens.
https://photographylife.com/what-is-diffraction-in-photography

When photographers talk about lens diffraction, they are referring to the fact that a photograph grows progressively less sharp at small aperture values – f/16, f/22, and so on. As you stop down your lens to such small apertures, the finest detail in your photographs will begin to blur.

A lens utilizes an aperture to help control depth of field, one of the most important tools in photography. However, leaving the aperture wide open will often result in slightly soft images, due to the lens's lack of ability to focus the light rays at that aperture. On the other hand, if you stop down too much, diffraction will also soften images because the extremely small aperture opening will bend the light in a different way, resulting in rays that aren’t accurately captured.
https://www.bhphotovideo.com/explora/photography/tips-and-solutions/lens-diffraction-what-it-and-how-avoid-it

[Bored chemist]

The diffraction is produced by the edges of the aperture, rather than the lens.

That is exactly what I said.
Why are you repeating it as if it's somehow news to us all?
Why waste that bandwidth?

[hamdani yusuf (OP)]

The diffraction is produced by the edges of the aperture, rather than the lens.

That is exactly what I said.
Why are you repeating it as if it's somehow news to us all?
Why waste that bandwidth?

What you seem not to realise is that a beam is only "finite" because it has been sent through some aperture.
In the case of a laser pointer, the aperture is inside the laser itself.
But there is always some sort of limit.
So the answer to "What made the beam narrow?" is always " a set of edges".

The edge of the lens will cause diffraction.

[Bored chemist]

The diffraction is produced by the edges of the aperture, rather than the lens.

That is exactly what I said.
Why are you repeating it as if it's somehow news to us all?
Why waste that bandwidth?

What you seem not to realise is that a beam is only "finite" because it has been sent through some aperture.
In the case of a laser pointer, the aperture is inside the laser itself.
But there is always some sort of limit.
So the answer to "What made the beam narrow?" is always " a set of edges".

The edge of the lens will cause diffraction.

You seem to  have forgotten to make any sort of point.

[hamdani yusuf (OP)]

The diffraction is produced by the edges of the aperture, rather than the lens.

That is exactly what I said.
Why are you repeating it as if it's somehow news to us all?
Why waste that bandwidth?

What you seem not to realise is that a beam is only "finite" because it has been sent through some aperture.
In the case of a laser pointer, the aperture is inside the laser itself.
But there is always some sort of limit.
So the answer to "What made the beam narrow?" is always " a set of edges".

The edge of the lens will cause diffraction.

You seem to  have forgotten to make any sort of point.

You seem to  have forgotten what you've said previously.

[Bored chemist]

You seem to  have forgotten what you've said previously.

It only seems that way to you.
All the things I said are consistent with each other.
Do you understand that an aperture and an edge mean the same thing?
The only reason you have a beam of finite width is that something got in the way of light outside the beam.

[hamdani yusuf (OP)]

Young's interference experiment with single photons (Hamamatsu Photonics, 1982)
This experiment, conducted by Hamamatsu Photonics in 1981,  captured the dual nature of the photon by a special camera for the first time ever in the world.

It seems that this kind of experiments have convinced people that light consists of particles called photon.