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Atomic nucleus excited with laser: A breakthrough after decades

tuwien.at

11–20 of 229 posts

Re: Atomic nucleus excited with laser: A breakthrough after decades

#11

> If the wavelength of the laser is chosen exactly right ... then maybe a special atomic nucleus could be manipulated with a laser, namely thorium-229. On November 21, 2023, the team was finally successful: the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time. So what's the wavelength? I felt like the article left me hanging. The answer is: 148.3…

I guess they could have said the laser frequency is about 2.02 petahertz

Re: Atomic nucleus excited with laser: A breakthrough after decades

#12
post #10

What does "exciting a nucleus" mean?

Not a physicist but "exciting" a thing means to make it oscillate e.g. by adding energy into the system. A violin player is exciting the string of her instrument using a bow.

Now in this case they use lasers. I suspect if you choose the right wavelenght (=frequency) of light there is some sort of resonance phenomenom.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#13
post #10

What does "exciting a nucleus" mean?

The article mentions switching between "energy states":

> This nucleus has two very closely adjacent energy states – so closely adjacent that a laser should in principle be sufficient to change the state of the atomic nucleus.

> the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time. The laser beam had actually switched their state.

I don't know enough to explain any further.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#16

> If the wavelength of the laser is chosen exactly right ... then maybe a special atomic nucleus could be manipulated with a laser, namely thorium-229. On November 21, 2023, the team was finally successful: the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time. So what's the wavelength? I felt like the article left me hanging. The answer is: 148.3…

Oh that's about 0.0000000014 football fields.

More seriously, apparently it takes a photon with a wavelength of 92nm to eject an electron from a hydrogen atom. Maybe this is a reasonable reference/refresher: https://web.archive.org/web/20210413042937/https://www.nagwa...

Re: Atomic nucleus excited with laser: A breakthrough after decades

#17
post #10

What does "exciting a nucleus" mean?

It means getting the nucleus to absorb a certain energy above its ground state. Since it is a quantum object, it can only absorb/emit energy in very specific amounts at once (“quanta”).

The details of how the nucleus manifests that extra energy are complicated, but you can imagine it as like, picking up a certain vibrational frequency.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#18
post #10

What does "exciting a nucleus" mean?

Thorium-229 has two energy states. A ground state, and an excited isometric state. The laser is used to transition the nucleus from the ground state to the excited isometric state.

And then?

Re: Atomic nucleus excited with laser: A breakthrough after decades

#19
post #2

> This makes it possible to combine two areas of physics that previously had little to do with each other: classical quantum physics and nuclear physics. Is quantum physics now considered part of classical physics? If so then man, time flies!

We currently don’t know how to calculate the nucleus’s bound state despite a thorough understanding of individual pieces that make it together, as explored in colliders like CERN and others. The problem is similar to telling at what temperature water is boiling, freezing, and its density from knowing the properties of a single water molecule. We understand quantum mechanics and Columb forces govern the properties; it is incredibly hard to renormalise the system from an energy scale of a gas to a liquid or solid. Similarly, it is for a quark-gluon plasma; thus, phenomenological models are used, like how the nuclear potential could look and the masses for different combinations of nuclei.

Re: Atomic nucleus excited with laser: A breakthrough after decades

#20
> It could be used, for example, to build an nuclear clock that could measure time more precisely than the best atomic clocks available today.

Are today's atomic clocks really so imprecise? Without further explanation of this, it reminds me of this comic (which is alas showing its age both by mentioning flash, and by implying that 1024 is already a uselessly high number of cpus to support):

https://xkcd.com/619/

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