[Bored chemist]

They should have said "putting a lens in front of a torch".
Because that's what they did.

What's the consequences of "putting a lens in front of a torch"?
What's the intensity of the focused light? Is it the same as the unfocused one?

Watch the video and find out.
Or do teh experiemnt yourself.

[Bored chemist]

How to cool things using light other than laser?

The same way that you would do it using a laser, but using a different light source.
The fact that you ask this proves that you don't understand how laser cooling works.

So, it only works in theory, then. Perhaps the theory that you believe hasn't completely describe physical reality yet.

Could you read a book by sunlight if you were on Mars  (In a suitable space-suit)?
Nobody has tried.
Any answer would be theoretical.
But would you expect the theory to be wrong.

I did, in fact, explain why my prediction is correct.
It's just that you didn't understand it.

an atom hit by a photon does not know if that photon came from a laser or a camp fire

[alancalverd]

What's the intensity of the focused light?

And there's the second problem with the video! The lumen is a psychophysical unit as it multiplies the actual spectral radiance by the very nonlinear photopic luminous efficiency function of the average human eye, so focussing the output of a non-monochromatic source of n lumens onto any other receptor does not produce a calculable result.

If, for instance, the source is entirely infrared, you could fry a steak with zero lumens but lots of watts. I used to use this simple phenomenon to demonstrate the hazards of surgical  CO2 lasers.

[alancalverd]

Your claim above contradicts Gemini. You sound like non-laser cooling were already widely known, despite their inefficiency.

No contradiction. The theory of photonic cooling predates the demonstration and is based on photons with no reference to their source. The practical application uses lasers as the most efficient source of coherent radiation.

[hamdani yusuf (OP)]

an atom hit by a photon does not know if that photon came from a laser or a camp fire

But laser cooling doesn't only work with single atom and single photon. The temporal relationship with subsequent photons are critical in determining whether the interaction ends up with net cooling or heating instead.
Non-laser sources generally lack of coherence to do the job.

Gemini
Laser cooling is a counterintuitive process where lasers are used to cool atoms or molecules to incredibly low temperatures, often approaching absolute zero. This might seem strange because lasers are typically associated with heat and energy, but the underlying physics is quite fascinating.
How Does it Work?
The principle is based on the interaction between light and matter. When an atom absorbs a photon (a particle of light), it gains momentum in the direction of the photon's travel. However, when the atom re-emits the photon, it does so in a random direction.
By carefully tuning the laser's frequency and direction, scientists can ensure that atoms moving towards the laser are more likely to absorb photons than those moving away. This results in a net slowing down of the atoms, effectively cooling them.

[alancalverd]

If one atom has no knowledge of the source of the photon, it is reasonable to assume that all the others are equally ignorant.

The gap between theory and practice is often closed by an invention from a very different field: witness the impact of the internal combustion engine, originally intended for road transport, on the development of human flight.

[Bored chemist]

But laser cooling doesn't only work with single atom and single photon.

If you look really carefully, you will see that nobody said it did.

I'm pretty sure I have pointed out that "temperature" is only well defined for an ensemble of particles.

Also, if you look carefully here
"The principle is based on the interaction between light and matter. When an atom absorbs a photon (a particle of light), it gains momentum in the direction of the photon's travel. However, when the atom re-emits the photon, it does so in a random direction.
By carefully tuning the laser's frequency and direction, scientists can ensure that atoms moving towards the laser are more likely to absorb photons than those moving away. This results in a net slowing down of the atoms, effectively cooling them."
you will see they talk about frequency and direction, but not coherence.

That's because coherence is not required.
Which is why you don't need a laser. (Though , as I have pointed out, you can get coherent light without using a laser- just like Gabor did)

Sure, using a laser is the only practical option but, in principle it's not the only option.

So the "negative temperature" inside a laser is not the reason it can cool stuff

[hamdani yusuf (OP)]

If one atom has no knowledge of the source of the photon, it is reasonable to assume that all the others are equally ignorant.

The gap between theory and practice is often closed by an invention from a very different field: witness the impact of the internal combustion engine, originally intended for road transport, on the development of human flight.

Then they would fail to produce interference pattern in a double slit experiment.

[hamdani yusuf (OP)]

That's because coherence is not required.
Which is why you don't need a laser. (Though , as I have pointed out, you can get coherent light without using a laser- just like Gabor did)

Here's what Wikipedia says:

Optical holography needs a laser light to record the light field.
https://en.wikipedia.org/wiki/Holography

The Hungarian-British physicist Dennis Gabor invented holography in 1948 while he was looking for a way to improve image resolution in electron microscopes.[6][7][8] Gabor's work was built on pioneering work in the field of X-ray microscopy by other scientists including Mieczysław Wolfke in 1920 and William Lawrence Bragg in 1939.[9] The formulation of holography was an unexpected result of Gabor's research into improving electron microscopes at the British Thomson-Houston Company (BTH) in Rugby, England, and the company filed a patent in December 1947 (patent GB685286). The technique as originally invented is still used in electron microscopy, where it is known as electron holography. Gabor was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method".[10]

Optical holography did not really advance until the development of the laser in 1960. The development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union[11] and by Emmett Leith and Juris Upatnieks at the University of Michigan, US.[12]
https://en.wikipedia.org/wiki/Holography#History

[hamdani yusuf (OP)]

So the "negative temperature" inside a laser is not the reason it can cool stuff

I don't agree with the description of laser as negative temperature either.
I agree with Dr. Michelsen's statement that its temperature is not well defined for not being a system in equilibrium. The same situation applies to radio and microwave transmitters.

[alancalverd]

I don't agree with the description of laser as negative temperature either.

It's worth reading the Wikipedia entry on the subject, to understand the concept. Nothing to do with "agreement", but a matter of definition of an unusual phenomenon.

[Bored chemist]

Here's what Wikipedia says:

Optical holography needs a laser light to record the light field.

The Hungarian-British physicist Dennis Gabor invented holography in 1948

Here's what wiki also says

"On May 16, 1960, Theodore H. Maiman operated the first functioning laser
from"
https://en.wikipedia.org/wiki/Laser#History

Are you saying that Gabor time traveled forward from 1948 to 1960 in order to borrow a laser?

Do you not realise that "you need a laser to do holography" is another of the "lies we tell to children"?


Didn't it occur to you that I might simply have been correct when I said this?
 "

(Though , as I have pointed out, you can get coherent light without using a laser- just like Gabor did)

[Bored chemist]

I agree with Dr. Michelsen's statement that its temperature is not well defined for not being a system in equilibrium.

More pertinently, you agree with me.

I'm pretty sure I have pointed out that "temperature" is only well defined for an ensemble of particles.

[hamdani yusuf (OP)]

Are you saying that Gabor time traveled forward from 1948 to 1960 in order to borrow a laser?

The Wikipedia article says that Gabor invented electron holography.

[hamdani yusuf (OP)]

Nothing to do with "agreement", but a matter of definition of an unusual phenomenon.

You can agree or disagree on how other people define things.

[alancalverd]

Not in science. Words have precise meanings assigned to them by the inventor or discoverer, or by bodies such as the International Standards Organisation. That way we can communicate and build rather than argue or philosophise.

[hamdani yusuf (OP)]

Not in science. Words have precise meanings assigned to them by the inventor or discoverer, or by bodies such as the International Standards Organisation. That way we can communicate and build rather than argue or philosophise.

We disagreed on how Feynman defined diffraction.

[Bored chemist]

Not in science. Words have precise meanings assigned to them by the inventor or discoverer, or by bodies such as the International Standards Organisation. That way we can communicate and build rather than argue or philosophise.

We disagreed on how Feynman defined diffraction.

If he was still alive, you could resolve that..But he's not and it's hard to see how it matters.

[alancalverd]

We disagreed on how Feynman defined diffraction.

Feynman was an individual, not a consensus, and did not discover diffraction.

[hamdani yusuf (OP)]

We disagreed on how Feynman defined diffraction.

Feynman was an individual, not a consensus, and did not discover diffraction.

The one who discovers a phenomenon isn't always the same one who gives it the name that ends up as consensus.