Telescope amplification with laser medium?

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jseah
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Telescope amplification with laser medium?

Postby jseah » Sat Jun 10, 2017 11:58 pm UTC

I had a random idea that didn't seem to be obviously wrong at first but I can't find anything about it.

The idea is that since stimulated emission produces coherent photons, you can use a lasing medium to amplifying incoming photons hitting a telescope lens. If you don't bounce the beam back and forth through the medium and simply rely on a single pass through (ie contain the lasing medium between two perfectly flat transparent 'lenses'), this would cause the photon count to increase without affecting the image, no?

It doesn't obviously break physics either since you have to input energy into the lasing medium anyway.


The only downside I can think of would be that your telescope would only operate on a single frequency.
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Re: Telescope amplification with laser medium?

Postby ucim » Sun Jun 11, 2017 2:28 am UTC

Well, you'd get coherent (and colinear) photons, but that's not what you want. The slight non-colinearity of the incoming photons is what creates an image. So, for optical telescopes, that would be a bit of a downside. There are other photon amplification methods employed at the imaging plane.

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Re: Telescope amplification with laser medium?

Postby reval » Mon Jun 12, 2017 1:36 am UTC

So it would only amplify on a single frequency at a time. Any way to tune the frequency? Sweep it through a range and get a spectrum? Amp up your signal for oxygen or whatever.

I like it. I have no idea whether it would work or what's wrong with it either.

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Re: Telescope amplification with laser medium?

Postby Zamfir » Mon Jun 12, 2017 9:39 am UTC

There are "optical amplifiers" that are close to what you describe. Those take a laser beam in and generate an amplified beam through optical means only (similar to what you describe). They are used to extend the range of fibre optic channels. These replaced older repeaters that would use an optical-to-electronic sensor, and then send out a new beam based on the electronic signal.

AFAIK, these optic amplifiers are less sensitive than electronic sensors. The advantage is that they are faster than decoding-then-encoding, and they can amplify a signal without understanding its exact encoding. So it's not obvious that this is useful for astronomy. But the principle exist, and there might be developments in the future.

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Re: Telescope amplification with laser medium?

Postby quantropy » Tue Jun 13, 2017 9:53 am UTC

I think that the main problem with your idea is that lasers are forbidden by the laws of quantum theory.

Yes, Einstein proposed the theory of stimulated emission in 1917, but everyone knows that Einstein was wrong about quantum theory, and by the 1940's it was known that such a thing was not allowed. But in 1951 along came Charles Townes who wanted a strong source of microwaves, and so built a maser, despite it not being allowed. (The laser came a bit later). Lasers were soon seen as a great success of quantum theory. Then in 1982 Nick Herbert invented FLASH, which used a laser for superluminal communication.

Yes lasers work, but the simple explanation in terms of the duplication of individual photons is not allowed by quantum theory. It looks like your idea needs this, and so would not work.

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Re: Telescope amplification with laser medium?

Postby morriswalters » Tue Jun 13, 2017 11:34 am UTC

Naively, I question the point. What new information does this get you? Telescopes gather light, they measure signal over time. Or so I have always believed. And everything astronomers can use is encoded in the signal. I appears to me that the intensity is only important relative to the observed field. Is pixel a brighter than pixel b?

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Re: Telescope amplification with laser medium?

Postby Zamfir » Tue Jun 13, 2017 2:19 pm UTC

Naively, I question the point. What new information does this get you?

If optical amplification introduces less noise than electronic amplification, then it makes sense to amplify the light before you let it hit a sensor. The combined system would have a higher sensitivity (it could measure smaller differences in light strength). But that's just hypothetically speaking - I don't think optical amplification is especially free from noise.

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Re: Telescope amplification with laser medium?

Postby morriswalters » Tue Jun 13, 2017 7:10 pm UTC

Ok. Well, night vision lens are based on image amplifiers. And evidently ESA has launched a super conducting camera which counts photons pretty well.

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Re: Telescope amplification with laser medium?

Postby Eebster the Great » Wed Jun 14, 2017 3:29 pm UTC

quantropy wrote:I think that the main problem with your idea is that lasers are forbidden by the laws of quantum theory.

Yes, Einstein proposed the theory of stimulated emission in 1917, but everyone knows that Einstein was wrong about quantum theory, and by the 1940's it was known that such a thing was not allowed. But in 1951 along came Charles Townes who wanted a strong source of microwaves, and so built a maser, despite it not being allowed. (The laser came a bit later). Lasers were soon seen as a great success of quantum theory. Then in 1982 Nick Herbert invented FLASH, which used a laser for superluminal communication.

Yes lasers work, but the simple explanation in terms of the duplication of individual photons is not allowed by quantum theory. It looks like your idea needs this, and so would not work.

Wat

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Re: Telescope amplification with laser medium?

Postby quantropy » Wed Jun 14, 2017 4:47 pm UTC

Eebster the Great wrote:Wat

You can find more in the books How the Laser happened and How the Hippies saved physics

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Re: Telescope amplification with laser medium?

Postby Copper Bezel » Wed Jun 14, 2017 10:12 pm UTC

There are details of that explanation that match events I didn't know about that happened in this universe. I'm still not quite sure which bits are exclusive to the parallel one said text came from.
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Eebster the Great
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Re: Telescope amplification with laser medium?

Postby Eebster the Great » Wed Jun 14, 2017 10:58 pm UTC

quantropy wrote:
Eebster the Great wrote:Wat

You can find more in the books How the Laser happened and How the Hippies saved physics

I skimmed the Sci Am article and didn't see anything about how lasers violate the laws of physics. Can you expand on what exactly they do that is so impossible?

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Re: Telescope amplification with laser medium?

Postby morriswalters » Thu Jun 15, 2017 2:37 am UTC

It appears to have been meant as humor. This on the other hand.
quantropy wrote:Yes lasers work, but the simple explanation in terms of the duplication of individual photons is not allowed by quantum theory.
Would seem to be a refutation of the idea of using the laser. The humor comes from the fact something can be known as a fact until somebody comes along with new facts.

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Re: Telescope amplification with laser medium?

Postby quantropy » Thu Jun 15, 2017 9:54 am UTC

Eebster the Great wrote:I skimmed the Sci Am article and didn't see anything about how lasers violate the laws of physics. Can you expand on what exactly they do that is so impossible?

When Charles Townes worked on using stimulated emission to provide a source of microwaves he was told in no uncertain terms that he was wasting his time since this was not possible. (Fortunately he had sufficient job security, otherwise he'd probably have been fired.) When he succeeded, John von Neumann said 'That can't be right' and Niels Bohr said 'But that is not possible'. ( How the Laser Happened)

In 1982 Nick Herbert designed FLASH which used stimulated emission to duplicate a photon. If you can duplicate a photon you can use Bell's inequalities to transmit information faster than light. This seemed unlikely and soon the no-cloning theorem was developed to explain why it wouldn't work.
(How the hippies saved physics)

So the explanation that stimulated emission will take a photon and produce an exact copy is what violates the laws of physics. This means that this can't be how lasers actually work, and any device which relies on using stimulated emission to copy photons in this way won't work.

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Re: Telescope amplification with laser medium?

Postby Eebster the Great » Fri Jun 16, 2017 12:42 am UTC

quantropy wrote:
Eebster the Great wrote:I skimmed the Sci Am article and didn't see anything about how lasers violate the laws of physics. Can you expand on what exactly they do that is so impossible?

When Charles Townes worked on using stimulated emission to provide a source of microwaves he was told in no uncertain terms that he was wasting his time since this was not possible. (Fortunately he had sufficient job security, otherwise he'd probably have been fired.) When he succeeded, John von Neumann said 'That can't be right' and Niels Bohr said 'But that is not possible'. ( How the Laser Happened)

In 1982 Nick Herbert designed FLASH which used stimulated emission to duplicate a photon. If you can duplicate a photon you can use Bell's inequalities to transmit information faster than light. This seemed unlikely and soon the no-cloning theorem was developed to explain why it wouldn't work.
(How the hippies saved physics)

So the explanation that stimulated emission will take a photon and produce an exact copy is what violates the laws of physics. This means that this can't be how lasers actually work, and any device which relies on using stimulated emission to copy photons in this way won't work.

I see, thanks. Yes, copying quantum states is definitely impossible. I had never heard that people thought this was how lasers worked.

What you said at first was that lasers were impossible, which is a very strange thing to say since I have a bunch of lasers here with me in the room.

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Re: Telescope amplification with laser medium?

Postby Copper Bezel » Fri Jun 16, 2017 6:03 pm UTC

I think the conceit is that the phenomenon is unexplained and unexplained phenomena are impossible in (theoretical) physics. The latter is technically true as an ironic statement in reminder of our limitations, but yeah, if there's any truth to the former at all, I'm not aware of it, either.
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Re: Telescope amplification with laser medium?

Postby mfb » Mon Jul 03, 2017 11:53 pm UTC

To come back to actual physics:

We have detectors that can detect ~80% of the incoming photons over a large wavelength range. It is hard to beat that. Laser-like light amplification would limit you to a very narrow wavelength range, and you would sometimes get photons from spontaneous transitions - you increase your background.

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Re: Telescope amplification with laser medium?

Postby LaserGuy » Mon Jul 10, 2017 11:10 pm UTC

Not only that, but we can already get eight orders of magnitude in signal amplification from the detector itself. Single-pass optical amplifiers can't get those sort of gains, so I'm not sure what the benefit would be. Single-photon amplification is not particularly easy to do anyway, so I'm not sure if this is even technically feasible.

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Re: Telescope amplification with laser medium?

Postby Frenetic Pony » Fri Jul 14, 2017 9:48 am UTC

Errr, it's still the same signal. You aren't actually "boosting" the amount of signal at all, you're just making it bigger for... well really for no reason. So the distant photon comes in, either hits a standard photodetector and gets converted into an electron at the percentage of efficiency/quantum blah blah blah and you read it out. Or in your system stimulates some bouncing laser thing, that has ideally the exact same efficiency/quantum blah blah blah limits that the standard photodetector has.

It just seems like an extra unnecessary step. One that, thanks to quantum blah blah blah insert measurements changing the outcome/vacuum interference/etc. should just distort the signal you're getting somewhat without actually increasing the chance that you're getting it. Cameras already "boost" the signal they get while converting from analog to digital, and already need to deal with noise from that. The initial boost is just to get it to convert to digital cleanly, the less you have to boost the get it into digital the less noise you get. The goal would actually be to not boost the signal at all and convert it cleanly, 1 to 1, to a digital signal, amplification just ruins the signal.


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