
Gamma-ray laser moves a step closer to reality - dnetesn
https://phys.org/news/2019-12-gamma-ray-laser-closer-reality.html
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yummypaint
If you're curious about the current state of the art see the high inte sity
gamma source:
[http://faculty.virginia.edu/PSTP2013/Talks/HIGSCapabilities_...](http://faculty.virginia.edu/PSTP2013/Talks/HIGSCapabilities_PSTP2013_v2.pdf)

This isnt a gamma laser because the gamma rays arent coherent, but they can be
polarized more than 99%. The free electron laser makes optical laser light in
a big cavity with dielectric mirrors, the next electron bunch in the storage
ring collides with it and scatters it up to MeV level of energy. Flux and
energy resolution can be exchanged by changing the diameter of the gamma
collimator and the operating mode. Its generally something like 10^7 gammas/s
for energies near 15 MeV with 3% resolution.

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DoofusOfDeath
Newbie question: Aren't gamma rays just a particular frequency range of e.m.?
If so, why would they be any less capable of coherence than other e.m.
frequencies?

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yummypaint
That is true that photons are photons, the trick is getting them to be
coherent in the first place. Optical lasers use stimulated emission in some
form. I presume that positronium from the article is able to somehow also
undergo stimulated emission in the form of the particles anihilating and
making 511 kev photons. The distinction between that and how HIGS works is
that HIGS is effectively bouncing laser light off a fast moving mirror made of
electrons, which actually destroys the coherence, even though the resulting
gamma rays are still very similar.

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londons_explore
To me this looks like someone has used a markov chain to massage together some
buzzwords into something grammatically correct...

Can someone actually in the field comment on the legit-ness of this article?

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jiggawatts
The physics appears to be kosher, but I can't speak about the practicality of
such as device. I suspect it's up there with graphene in that it'll generate a
lot of papers, but no industrial applications.

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hammock
It sounds like a powerful weapon to me.

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LatteLazy
Not that I'm opposed to speculative research but...

Does anyone know any actual uses for such a device? I know the article says
medical and space propulsion. But it doesn't seem well suited to space
propulsion (seems like a dangerous exhaust that doesn't do anything a
microwave deam doesn't?).

Sorry if I'm being dull

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Gatsky
I think the idea is to achieve extreme energy densities and a high degree of
control, with many practical benefits over a particle accelerator. This old
article describes some of the stuff they were doing with a petawatt laser [0].

Essentially, they used it for microscale imaging and also generating extremely
high energy electrons. There is also 'photofission' where gamma rays cause
nuclear fission to occur [1]. There is some additional detail in this article
[2]. They seem to be saying that obviously photon-electron interactions are
incredibly useful in science, and a gamma ray laser would be just as useful
but for photon-nuclear interactions.

Finally of course, a gamma ray laser would be a useful space weapon. For
example, at [1] they could penetrate 6 inches of lead. It isn't clear how you
could reliably stop a high energy gamma laser, as it would degrade even very
dense shielding at the same time as generating showers of ultra high energy
electrons, neutrons and protons.

[0]
[https://web.archive.org/web/20080614224504/http://newton.ex....](https://web.archive.org/web/20080614224504/http://newton.ex.ac.uk/aip/physnews.401.html#3)

[1]
[https://en.wikipedia.org/wiki/Photofission](https://en.wikipedia.org/wiki/Photofission)

[2] [https://spie.org/news/3681-nuclear-photonics-with-laser-
base...](https://spie.org/news/3681-nuclear-photonics-with-laser-based-gamma-
rays#B4)

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londons_explore
Surely to make a gamma laser, you at a minimum need a gamma mirror.

To my knowledge, such things don't exist (current gamma mirrors aren't 'shiny'
\- ie. they don't reflect the light, but instead diffuse it).

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ggm
Coherence doesn't depend on the mirror, that's surely just about efficiency? I
thought coherence came from quantum states of the lasing medium.

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hoseja
Coherent radiation in all directions usually isn't something that one imagines
when hearing 'LASER'.

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ggm
Put it in a giant tank of water with one exit hole. Highly inefficient...

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dr_dshiv
I'd hypothesize that this would be useful for producing matter + anti-matter
pairs

