Delayed time zero in photoemission: New record in time measurement accuracy

Jun 24, 2010
The photoemission of electrons by an attosecond light pulse (blue beam) is time resolved by controlling the electron motion with an ultrashort visible laser pulse (shown as red beam). This attosecond streaking uncovers that electrons from different atomic orbitals are released with a delay comparable to the atomic unit of time. Credit: Photograph: Thorsten Naeser / Max-Planck-Institute of Quantum Optics

German physicists have discovered a time delay when using light pulses to emit electrons from atoms. Until now, it has been assumed that the electrons start moving out of the atom immediately after the impact of the photons. This delay is the shortest time interval measured to date. Science journal reports on their findings in the tomorrow's issue.

When light is absorbed by , the electrons become excited. If the , so-called photons, carry sufficient energy, the electrons can be ejected from the atom. This effect is known as photoemission and was explained by Einstein more than hundred years ago. Until now, it has been assumed that the electron start moving out of the atom immediately after the impact of the photon. This point in time can be detected and has so far been considered as coincident with the arrival time of the , i.e. with "time zero" in the interaction of light with matter.

Using their ultra-short time measurement technology, physicists from the Laboratory for Attosecond Physics at the Max Planck Institute of Quantum Optics (MPQ), the Technische Universitaet Muenchen (TUM) and the Ludwig-Maximilians-Universitaet Munich (LMU) along with collaborators from Austria, Greece, and Saudi Arabia, have now tested this assumption.

The physicists fired pulses of near-infrared laser light lasting less than four femtoseconds (10-15 seconds) at atoms of the noble gas neon. The atoms were simultaneously hit by extreme ultraviolet pulses with a duration of 180 attoseconds, liberating electrons from their atomic orbitals. The attosecond flashes ejected electrons either from the outer 2p-orbitals or from the inner 2s-orbitals of the atom. With the controlled field of the synchronised laser pulse serving as an "attosecond chronograph", the physicists then recorded when the excited electrons left the atom.

Their measurements revealed that electrons from different atomic orbitals, although excited simultaneously, leave the atom with a small but measurable time delay of about twenty attoseconds. "One attosecond is one billionth of one billionth of a second, an unimaginable short interval of time. But after excitation by light one of the electrons leaves the atom earlier than the other. Hence we were able to show that electrons "hesitate" briefly before they leave an atom," explains Reinhard Kienberger, Professor for Experimental Physics (E 11) at the TUM and head of the Junior Research Group Dynamics at the MPQ.

Determining the cause of this hesitation was also a challenge to the LAP theorists around Dr. Vladislav Yakovlev and his colleagues from the Vienna University of Technology (Austria) and the National Hellenic Research Foundation (Greece). Although they could confirm the effect qualitatively using complicated computations, they came up with a time offset of only five attoseconds. The cause of this discrepancy may lie in the complexity of the neon atom, which consists, in addition to the nucleus, of ten electrons. "The computational effort required to model such a many-electron system exceeds the computational capacity of today's supercomputers," explains Yakovlev.

Nevertheless, these investigations already point toward a probable cause of the "hesitation" of the electrons: the electrons interact not only with their atomic nucleus, but they are also influenced by one another. "This electron-electron interaction may then mean that it takes a short while before an electron that is shaken by the incident light wave is released by its fellow electrons and allowed to leave the atom," sais Dr. Martin Schulze, Postdoc at the LAP-Team.

"These to-date poorly understood interactions have a fundamental influence on electron movements in tiniest dimensions, which determine the course of all biological and chemical processes, not to mention the speed of microprocessors, which lie at the heart of computers", explains Ferenc Krausz. "Our investigations shed on the electrons' interactions with one another on atomic scale". To this end, the fastest measuring technique in the world is just about good enough: the observed 20-attosecond time offset in the ejection times of is the shortest interval that has ever been directly measured.

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Provided by Technische Universitaet Muenchen

4.9 /5 (26 votes)

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zevkirsh
5 / 5 (1) Jun 24, 2010
ive always wondered by goodbye's always take so long.
TehDog
5 / 5 (2) Jun 24, 2010
But after excitation by light one of the electrons leaves the atom earlier than the other. Hence we were able to show that electrons "hesitate" briefly before they leave an atom," explains Reinhard Kienberger

Nevertheless, these investigations already point toward a probable cause of the "hesitation" of the electrons: the electrons interact not only with their atomic nucleus, but they are also influenced by one another. "This electron-electron interaction may then mean that it takes a short while before an electron that is shaken by the incident light wave is released by its fellow electrons and allowed to leave the atom," sais Dr. Martin Schulze, Postdoc at the LAP-Team.

Sorry about this...

"After you" "No I insist" (Holds door open...)
"Why thank you kind sir..."
Again, apologies :)
chandram
1 / 5 (1) Jun 25, 2010
There is instantaneity limited only by our capability of masring shorter and shorter times. Otherwise no two processes can take place simultaneously ever!
jsa09
not rated yet Jun 25, 2010
wonder how much influence this delay has on light absorption lines and if it contributes to red shift. I think it probably does but I would like to see experiment confirm one way or the other.
enginarc
5 / 5 (1) Jun 25, 2010
"Until now, it has been assumed that the electrons start moving out of the atom immediately after the impact of the photons. This delay is the shortest time interval measured to date."

IMO no action->reaction can be immediate, why did the scientists believed this in the first place.

After all our measurements are limited to the precision of the tools we use. Progress...
Skeptic_Heretic
not rated yet Jun 25, 2010
This effect is known as photoemission and was explained by Einstein more than hundred years ago.
Actually it was explained by Hertz in 1887 with the photoelectric effect however the majority of people didn't think atoms were real up until Einstein proved it in the early 1900's.
johanfprins
2.6 / 5 (5) Jun 25, 2010
It is exactly to be expected and the reason for this "hesitation" is simple: The incoming photon does not "collide" with the electron-wave but gets trapped by it; just like a light pulse can be trapped within a BEC. This adds to the energy of the standing wave for a time interval (del)t as limited by Heisenberg's "uncertainty" relationship for energy and time. This time interval is determined by the characteristics of the electron-wave (shape, size, energy) and is thus different for the different standing waves around the nucleus.

This behaviour is further proof that a photon is NOT a particle and that the photo-electric ejection of an electron is caused purely by a wave-wave resonant interaction. The light wave collapses and entangles with the electron-wave to increase its mass-energy. When the increased mass is more than an electron's rest mass, the electron is ejected. This model gives the same equation than the one Einstein derived in 1905.
SteveL
1 / 5 (2) Jun 25, 2010
Using both "near-infrared laser light" and "extreme ulraviolet" pulses - I see nothing about compensation for the differing light frequencies, or, does the process depend on a combined frequency harmonic to reach the energy level required to knock loose an electron?

I don't claim to be an expert in this field, but there's just not enough detail in this article for me to understand how the process actually works.
GSwift7
3 / 5 (2) Jun 25, 2010
"This behaviour is further proof that a photon is NOT a particle and that the photo-electric ejection of an electron is caused purely by a wave-wave resonant interaction"

Proof is too strong a word, but you're right that it seems to suggest another case where photons behave in a way that is consistent with what we have defined as a wave. Photons do not appear to fit neatly into that black-and-white particle-and-wave classification system. Trying to decide if a photon is a wave or a particle may be somewhat like trying to decide what kind of cat my pet bulldog is. It has a short tail, so it could be a short-tailed cat breed, but it has short hair similar to other cat breeds, so what kind of cat is a bulldog?
johanfprins
1 / 5 (3) Jun 25, 2010
Trying to decide if a photon is a wave or a particle may be somewhat like trying to decide what kind of cat my pet bulldog is. It has a short tail, so it could be a short-tailed cat breed, but it has short hair similar to other cat breeds, so what kind of cat is a bulldog?


I disagree strongly with this type of Alice-in-Wonderland reasoning: My, my the Copenhagen group REALLY did an excellent job in giving the physics community a frontal lobotomy. Where does a photon fit in any manner into the "particle classification" system. All we know is that a wave can diffract and interfere and THAT a particle cannot do so under ANY circumstances. Both moving electrons and light waves (even when such a wave has only a quantum of energy) diffract and interfere. So both MUST be waves and NOT particles: Which behaviour of these entities is that of "a particle" according to you?
Parsec
not rated yet Jun 25, 2010
AARRRGGHHH - everything is BOTH a particle and a wave. You can see this as a direct consequence of Heisenberg's calculations and isn't a consequence of any interpretation, Copenhagen or anyone else's. Finding a wave interpretation of the electron-photon collision is required by the implication of wave-particle duality. Also finding a particle explanation is equally required.
GSwift7
3 / 5 (2) Jun 25, 2010
@Johanfprins:

So, are you proposing Carver Mead's wave-only theory then? It's a plausible theory in many ways, but I tend to think the black body problem is related more to our flawed definitions, not the actual physics of the real world. I guess I'll concede that you have a good point, and that it's not so much that photons behave as particles, but that they behave in ways that suggest they aren't a wave, by our definition.
sender
not rated yet Jun 26, 2010
finally photoemissions could provably lead to optically tuned transistor bandgaps and oscillators which are exponentially faster than current consumer applications
johanfprins
1 / 5 (2) Jun 26, 2010
AARRRGGHHH - everything is BOTH a particle and a wave.

As I already said Heisenberg and co. really did an excellent job in giving the physics community a frontal lobotomy 1n 1927. Both Heisenberg's calculations and Schroedinger's equation is interpreted to imply that a stationary electron has a de Broglie wavelength. Hence this stupidity of wave-particle duality, complementarity and probability amplitudes. An electron around a nucleus cannot have ANY momentum since its energy is less than its rest mass energy. If it has momentum it will either radiate away its kinetic energy or it will move off. This is physics my boy! What you believe is fairytales. Has your father told you yet that father Xmas and the Tooth Fairy do not really exist?

By the way the intensity of a Schroedinger wave cannot be a probability distribuition EVER, since that would mean that the most proabable position to find an electron is zero for most of these waves.
johanfprins
1 / 5 (2) Jun 26, 2010
So, are you proposing Carver Mead's wave-only theory then?

Carver Mead is totally correct to proclaim "waves only". I am, however, not in accord with his alternative model. He misses the point that all standing waves (electron- and light-waves) have inertia, and that the energy of such a wave is thus only mass-energy.
I tend to think the black body problem is related more to our flawed definitions, ...

Our interpretation is flawed since it is assumed that there can be photons moving around in this cavity as if they are particles. The ONLY light waves that are allowed within the cavity are standing waves: UNLESS YOU IGNORE BOUNDARY CONDITIONS. When doing the latter one is doing VOODOO!

That there are quanta involved is due to the fact that the sources in the walls only emit waves with that energy. When such a wave enters the cavity it has to adapt to the new boundary conditions: It morphs and entangles to form part of an allowed standing wave. ALL WAVES ONLY!!
KBK
1 / 5 (3) Jun 26, 2010
Atomic polarization MUST occur between two adjacent structures before current flow can take place. This is also known as electron orbital polarization or alignment.

Funny that the people who are supposedly at the highest levels of scientific discovery did somehow not know that.

So, in an inductor, the polarization or alignment must race up the structure (wire length), ie an extension of the given voltage terminal of the give connected battery...and when the final or last few right at the other end of the wire or coil -at the other battery terminal- are finally aligned..then the whole chain can start transferring 'electrons'.

Until that time period takes place (polarization field racing down the wire), there is no current flow in the inductor.

This is the exact principle by which Joesph Newman extracts seeming 'free energy' from 900lb coils!

Same trick Tom Bearden uses.

Same Trick John Bedini uses.

It is a minor elastic/temporal aspect that can be resonated for 'free energy'.
KBK
1 / 5 (3) Jun 26, 2010
What you are looking at is the intermolecular atomic level actual mechanistic descriptive of the reasons behind lead and lag, voltage and Current, Capacitance and inductance, mass and magnetism.

Manipulable resonant and elastic vortex structures.

Do you see it now?

Obviously , gravity shows it's actual face in there too.

Then you get into the dimensional aspects...and whoooo..it gets easy to manipulate ....and the monkey starts to get scared.

Reality as you know it, starts to fall to pieces. And all those pieces become easy to move around.

Whoops!!
Jigga
1 / 5 (2) Jun 26, 2010
..until now, it has been assumed that the electrons start moving out of the atom immediately after the impact of the photons...
This is not true, here are some simulations of these transitions:

http://www.physik..._uk.html
NeuroPulse
not rated yet Jun 28, 2010
The light wave collapses and entangles with the electron-wave to increase its mass-energy. When the increased mass is more than an electron's rest mass, the electron is ejected.


Hello. Isn't the increased mass always more than the electron's rest mass by definition of "increase"? Do you mean the amount of the increase, that is, the difference between thew new mass and the rest mass? Thanks.
johanfprins
1.8 / 5 (5) Jun 28, 2010
Hello. Isn't the increased mass always more than the electron's rest mass by definition of "increase"? Do you mean the amount of the increase, that is, the difference between thew new mass and the rest mass? Thanks.

The fact that has been missed is that a "free" electron which is not moving relative to the nucleus has an energy equal to its rest mass. Thus to be bound at a nucleus, it must have a lower energy. Thus all bound electrons have mass-energies which are lower than their rest mass energy. If not they will not be bound electrons. Thus when a bound electron absorbs light its mass increases: If the latter increased mass is still less than its rest mass, the electron stays bound. If it is, however, more than its rest mass the electron is not bound anymore and is ejected as an intity that has kinetic energy. I hope this is more clear. Thanks for this valid question.
TehDog
1 / 5 (2) Jun 30, 2010
[massive snips]
Thus all bound electrons have mass-energies which are lower than their rest mass energy. If not they will not be bound electrons. Thus when a bound electron absorbs light its mass increases: If the latter increased mass is still less than its rest mass, the electron stays bound. If it is, however, more than its rest mass the electron is not bound anymore and is ejected as an intity that has kinetic energy. I hope this is more clear. Thanks for this valid question.

Sorry about the excessive quote, but I've finally got my head around this rest mass vs bound mass thing (I think, I don't intend to look at the maths :)
Regardless of it's validity, it provides a model that helps in thinking about this stuff.
And I like the wave only idea, would seem to simplify things. (I am not a scientist)

thanks johanfprins for making me think :)
johanfprins
2 / 5 (4) Jul 01, 2010
(I am not a scientist)
thanks johanfprins for making me think :)

I am aiming to reach people with common sense. For 10 years I thought that I will find them within the scientific community. This was not to be. Therefore I am now trying to involve non-scientists who are still willing and able to think outside the confines of dogma. People like you. I appreciate your compliment very much, Thanks TehDog.
SteveL
5 / 5 (1) Jul 02, 2010
Does the absorbtion of light by an electron gaining mass increase or decrease the electron's distance from the nucleus, and does it share the new energy level with other electrons in the same shell?
Jigga
1 / 5 (2) Jul 02, 2010
Mass or electron is 511 keV, which is 100.000x higher, then the energy of typical electron transitions. Such correction will be negative, but very subtle as measured by resulting distance of electron from atom nuclei. Resulting energy is shared, but this sharing is limited by Pauli's exclusion principle, Hund's rules, spin-orbit coupling, etc. This is why the number of spectral lines usually increases after electron excitation, until it obtains a character of continuous bands. The more excited and hot electrons are, the more they're distant from quantum scale driven by entanglement, the more they're behaving like true individualists, i.e. colliding particles of gas. This is why the light of hot discharge tube remains less colorful, then the light of cold one.
johanfprins
1 / 5 (2) Jul 02, 2010
Does the absorbtion of light by an electron gaining mass increase or decrease the electron's distance from the nucleus, and does it share the new energy level with other electrons in the same shell?

The gain in mass requires the electron to form a higher energy wave state; which is usually spread further from the nucleus. It thus morphs in shape and size to do this. For example, if an s-electron absorbs enough light-energy to become a p-electron, it has to morph in shape and size from being a spherical entity to be a dumbell entity. This morphing is what has been described as a "quantum jump". It HAS to occur near-instantaneously because a near-instantaneous change in boundary conditions (which obviously occurs for a near instantaneous increase in mass-energy) demands that it MUST do so.

When there is already a p-state electron in addition to the s-state electron, the latter electron can obviously not morph into this p-state unless it has an opposite spin; etc.
bluehigh
1 / 5 (1) Jul 02, 2010
No waves. No particles. Just objects of charge density with varying geometry that give rise to differing properties and can be associated with wave and/or particle like behaviour.

Are we limiting our understanding by excluding explanations other than waves or particles? Or is that we can not imagine other explanations?
johanfprins
1 / 5 (2) Jul 03, 2010
Are we limiting our understanding by excluding explanations other than waves or particles? Or is that we can not imagine other explanations?

The latter possibility does not feature in this discussion, and is therefore NOT excluded provided that new experimental data are found which require such a change in direction.

What is discussed is the fallacious argument by the Copenhagen group that two irreconcilable concepts, namely particles and waves are BOTH required to model nature. I am just pointing out that one can explain ALL known physics purely in terms of wave-fields; and when doing this classical physics, including Einstein's gravity, dovetails with quantum mechanics. This has not happenned and is probably not possible when assuming wave-particle complementarity. So why waste time with such an absurd concept?

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