Posted by
timothy
on from the yes-those-are-real-words dept.
bofh31337 writes: "Nature has an interesting story about the Lasetron. In theory, creating very short flashes of light, using high-powered lasers, you would be able to see inside atomic nuclei."
We would need higher frequency/lower wavelength light, not just short pulses of it.
You're right, for single photons. Sub-single-wavelength pulses are formed from many photons, of a variety of phases and colors. On average the peaks of the various photons add up to enormous values during the pulse.
If you've taken a class that discussed the Fourier transform, it's analogous to the impulse function, which is composed of all frequencies of sine waves. The sharper you want your impulse to be, the wider the range of frequencies you need to have in your pulse. These zeptosecond guys are using frequencies of light up to x-rays (!), which is how they get such short pulses.
--
-- Kuro5hin.org: where the good times never end.;-)
Yeah, but if you brush up on your Quantum Mechanics, you'll know that the shorter the wavelength, the more energy youre hitting your target with, with the photons.
This is no good as it disturbs the target too much (the old problem of quantum uncertainty) whereas I imagine that if the pulse is short enough and of something weaker than gamma rays, they can atleast get an image before the target is unusably perturbed.
BTW, they were talking about molecules and imaging chemical reactions, which may not be totally beyond light/soft-xrays wavelengths to do, arguably.
-- Anyone who considers arithmetical methods of producing random numbers is, of course, in a state of sin.-John von Neumann
Short pulses mean higher frequency/lower wavelength. Since a pulse of light has to be at least one photon, and a photon is one wave packet, then the duration of a pulse determines the minimum frequency/maximum wavelength of the light in that pulse. A one zeptosecond (10^-21 s) pulse would mean that the largest possible wavelength of a photon in that pulse whould be 3x10^-13 meters. This is somewhat smaller than an atom (approx 10^-9 meters), but still larger than a nucleus (approx 10^-15 meters). So with a pulse of this duration, we would definately be able to see an atom, and we might get a rater fuzzy picture of a nucleus.
Re:Zeptosecond?
by
JabberWokky
·
· Score: 3, Interesting
Hey... that's how these things start. I just hope they formalize it rather than stripping it away the way they did with terms for quarks.
--
Evan
-- "$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
One thing stands out unaddressed
by
CyberBlood
·
· Score: 4, Informative
As a physics student interested in research, I've learned that Nature generally hasn't been the most reputable science journal. In the past they've featured articles on faster than light motion, published very inaccurate results and later a story that was featured on Slashdot last April on a theorhetical quantum computer that functioned without necessarily being turned on.
Regarless, the point in the story that seems to be missing is how they don't address the Heisenberg Uncertainty Principle. Tracking the motions of electrons around nuclei generally isn't possible. The best we would be able to know would be one component of it's angular momentum and the rest will definitionally remain unknown.
Perhaps a better conceptualization would be the moon around the earth... It travels around the earth in a circular patter. This is about all we could know about the electron. Any other motions (like if the moon was also orbiting on a plane defined by earth's two poles) must remain unknown in quantum mechanics.
I would say read this with caution on what they claim they'd be able to do.
CyberBlood
Re:One thing stands out unaddressed
by
taxelxii
·
· Score: 3, Insightful
I'm also a physics student.
I don't think "tracking the motions of electrons around the nucleus" is what they are trying to do. Most of the time, ultrafast spectroscopy (as in femtosecond spectroscopy) is done in a "pump-probe" setup. First you pump the sample with a femtosecond pulse, then you probe it with another femtosecond pulse, delayed in time. You just have to look at the way the probe is transmitted in function of delay time to see the living times of excited states..
I think this may be more like what they want to do.. study the nucleus dynamics, or as they say in the text, their formation or fission,..
I do think that you were right on one point however, when you told that they did not adress the Uncertainty Principle. What puzzles me is how do they think they are going to use zeptosecond pulses. Pulses this short must have a very large bandwith (for comparison, 5fs pulses need to have about 300nm bandwith). Dispersion will be a huge problem if they ever want to steer the beam, or even focus it.
The idea is not to resolve sub-atomic features with visible light in way a classical optical microscopy works. The short wavelength light is needed to trigger the processes in nuclei which require high energy photons (MeV scale) and the short pulse duration is needed have the required time resolution, otherwise you would only see the final result without knowing how the system got there. Experiments with ultrashort light pulses are usually done in the so called Pump-Probe technique: With a first short light pulse (Pump) you trigger some process that you want to investigate in your sample, then after a certain time delay you shine a second light pulse (Probe) on your sample to "look" at state of the process. Doing many such Pump-Probe cycles with varying time delay between the pulses, you can "see" how the triggered process evolves (whereby "look" and "see" is not to be taken literally). In order to be able to do this your light pulses have to be shorter than the timescale of the process that you want to investigate. Chemical reactions and motion of electrons take place in the femtosecond regime, requiring fs-Lasers; nuclear reactions take place on the zeptosecond regime, requiring zs-Lasers.
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I always wondered what color those quarks really were...
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If you've taken a class that discussed the Fourier transform, it's analogous to the impulse function, which is composed of all frequencies of sine waves. The sharper you want your impulse to be, the wider the range of frequencies you need to have in your pulse. These zeptosecond guys are using frequencies of light up to x-rays (!), which is how they get such short pulses.
-- ;-)
Kuro5hin.org: where the good times never end.
Yeah, but if you brush up on your Quantum Mechanics, you'll know that the shorter the wavelength, the more energy youre hitting your target with, with the photons.
This is no good as it disturbs the target too much (the old problem of quantum uncertainty) whereas I imagine that if the pulse is short enough and of something weaker than gamma rays, they can atleast get an image before the target is unusably perturbed.
BTW, they were talking about molecules and imaging chemical reactions, which may not be totally beyond light/soft-xrays wavelengths to do, arguably.
Anyone who considers arithmetical methods of producing random numbers is, of course, in a state of sin.-John von Neumann
Short pulses mean higher frequency/lower wavelength. Since a pulse of light has to be at least one photon, and a photon is one wave packet, then the duration of a pulse determines the minimum frequency/maximum wavelength of the light in that pulse. A one zeptosecond (10^-21 s) pulse would mean that the largest possible wavelength of a photon in that pulse whould be 3x10^-13 meters. This is somewhat smaller than an atom (approx 10^-9 meters), but still larger than a nucleus (approx 10^-15 meters). So with a pulse of this duration, we would definately be able to see an atom, and we might get a rater fuzzy picture of a nucleus.
Hey... that's how these things start. I just hope they formalize it rather than stripping it away the way they did with terms for quarks.
--
Evan
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
As a physics student interested in research, I've learned that Nature generally hasn't been the most reputable science journal. In the past they've featured articles on faster than light motion, published very inaccurate results and later a story that was featured on Slashdot last April on a theorhetical quantum computer that functioned without necessarily being turned on.
Regarless, the point in the story that seems to be missing is how they don't address the Heisenberg Uncertainty Principle. Tracking the motions of electrons around nuclei generally isn't possible. The best we would be able to know would be one component of it's angular momentum and the rest will definitionally remain unknown.
Perhaps a better conceptualization would be the moon around the earth... It travels around the earth in a circular patter. This is about all we could know about the electron. Any other motions (like if the moon was also orbiting on a plane defined by earth's two poles) must remain unknown in quantum mechanics.
I would say read this with caution on what they claim they'd be able to do.
CyberBlood
The idea is not to resolve sub-atomic features with visible light in way a classical optical microscopy works. The short wavelength light is needed to trigger the processes in nuclei which require high energy photons (MeV scale) and the short pulse duration is needed have the required time resolution, otherwise you would only see the final result without knowing how the system got there. Experiments with ultrashort light pulses are usually done in the so called Pump-Probe technique: With a first short light pulse (Pump) you trigger some process that you want to investigate in your sample, then after a certain time delay you shine a second light pulse (Probe) on your sample to "look" at state of the process. Doing many such Pump-Probe cycles with varying time delay between the pulses, you can "see" how the triggered process evolves (whereby "look" and "see" is not to be taken literally). In order to be able to do this your light pulses have to be shorter than the timescale of the process that you want to investigate. Chemical reactions and motion of electrons take place in the femtosecond regime, requiring fs-Lasers; nuclear reactions take place on the zeptosecond regime, requiring zs-Lasers.