Superfast light pulses able to measure response time of electrons to light

February 4, 2016 by Bob Yirka report
Image credit: Credit: ORNL.gov

(Phys.org)—A team of researchers with members from Germany, the U.S. and Russia has found a way to measure the time it takes for an electron in an atom to respond to a pulse of light. In their paper published in the journal Nature, the team describes their use of a light field synthesizer to create pulses of light so fast that they were able to reveal the time it took for electrons in an atom to respond when struck. Kyung Taec Kim with the Gwangju Institute of Science offers a News & Views piece on the work done by the team in the same journal issue, outlining their work and noting one issue that still needs to be addressed with such work.

As scientists have begun preparing for the day when photons will replace in high speed computers, work is being done to better understand the link between the two. One important aspect of this is learning what happens when photons strike electrons that remain in their atom (rather than being knocked out of them), specifically, how long does it take them to respond.

To find this answer, the researchers used what has come to be known as a light-field synthesizer—it is a device that is able to produce pulses of light that are just half of a single wavelength long—something many had thought was impossible not too long ago. The pulses are of such short duration that they only last for the it takes to travel that half wavelength, which in this case, was approximately 380 attoseconds.

The light-field synthesizer works by combining several pulses of light brought together but slightly out of phase, allowing for canceling and ultimately, a single very short pulse. In their experiments, the researchers fired their super-short pulses at krypton held inside of a vacuum. In so doing, they found that it took the electrons 115 attoseconds to respond—the first such measurement of the response time of an electron to a visible light pulse.

The team plans to continue their work by looking at how electrons behave in other materials, and as Kim notes, finding a way to characterize both the amplitude and phase of radiation from atoms driven by a .

Explore further: Measuring the duration of energetic electron pulses using laser fields

More information: M. Th. Hassan et al. Optical attosecond pulses and tracking the nonlinear response of bound electrons, Nature (2016). DOI: 10.1038/nature16528

Abstract
The time it takes a bound electron to respond to the electromagnetic force of light sets a fundamental speed limit on the dynamic control of matter and electromagnetic signal processing. Time-integrated measurements of the nonlinear refractive index of matter indicate that the nonlinear response of bound electrons to optical fields is not instantaneous; however, a complete spectral characterization of the nonlinear susceptibility tensors—which is essential to deduce the temporal response of a medium to arbitrary driving forces using spectral measurements—has not yet been achieved. With the establishment of attosecond chronoscopy, the impulsive response of positive-energy electrons to electromagnetic fields has been explored through ionization of atoms and solids by an extreme-ultraviolet attosecond pulse or by strong near-infrared fields. However, none of the attosecond studies carried out so far have provided direct access to the nonlinear response of bound electrons. Here we demonstrate that intense optical attosecond pulses synthesized in the visible and nearby spectral ranges allow sub-femtosecond control and metrology of bound-electron dynamics. Vacuum ultraviolet spectra emanating from krypton atoms, exposed to intense waveform-controlled optical attosecond pulses, reveal a finite nonlinear response time of bound electrons of up to 115 attoseconds, which is sensitive to and controllable by the super-octave optical field. Our study could enable new spectroscopies of bound electrons in atomic, molecular or lattice potentials of solids, as well as light-based electronics operating on sub-femtosecond timescales and at petahertz rates.

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12 comments

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Whydening Gyre
5 / 5 (1) Feb 04, 2016
I'm confused... aren't wavelengths a measure of frequency? Which is variable?
KBK
1 / 5 (2) Feb 04, 2016
Classically, yes.

We've applied the nomenclature to the idea of electron and atomic time periods, but there's no way to say that the application of said framework is correct.

The map is not the territory ----and it is critical to always remember that in all physics exploration, lest the attempt at finding the new thing is caught up in being misrepresented by the labeling frenzies of physics history past.

This is a good example of how the arrow of time and arrow of physics exploration can be captured and mis-cast by the history of physics, and the humans who utilize it. The flaws of factual dogmatization and law creation within physics is a heinous crime of the first order, and is to be cast aside in all exploration so that new things can be found.

Simply put, if we lock the steering wheel of physics with factualization, dogma, and law, the only 'driven into' future that will be met, is one of steering into the ditch.
Phys1
5 / 5 (4) Feb 04, 2016
It is just half a period of a sine.
KBK
1 / 5 (2) Feb 04, 2016
Yes, but is the application of it to an 'electron wavelength', even remotely correct?

The answer is no.

It's a placeholder for an unrealized aspect that seems to behave in a similar way, but that is it. Nothing more.

Thus, one can use the idea of half a period of a sine in each expression of the words out loud or in the mind, as applied to an electron --- but....understand and know that it is just a mis-application of a thing we don't fully understand. A temporary label, for the purposes of building a model or argument.

One cannot gloss such a fundamental over, unless they wish to mislead themselves into thinking they are accurately driving a vehicle of exploration into a target that does not exist (meaning, drive into the ditch), as the steering was locked on a curvey road.

The more impossible a problem is to solve, the more fundamental the error in the formulation of the question.
Phys1
5 / 5 (8) Feb 04, 2016
@KBK
Think and study before you write this stuff.
Not electron, but light wavelength. The half wavelength pulse can be seen as a coherent superposition of many waves with different frequencies (and wavelengths) with the phases such that they all add up during half a sine and add up to zero outside this domain. The wavelength of the pulse is defined as the central wavelength of this distribution. You should read up on Fourier transformation.
Phys1
5 / 5 (5) Feb 04, 2016
@KBK
It irritates that you criticise excellent work without understanding the fundamentals.
Don't make it a habit.
antialias_physorg
5 / 5 (7) Feb 04, 2016
@KBK
It irritates that you criticise excellent work without understanding the fundamentals.
Don't make it a habit.

Unfortunately the guy has been around for quite some years, The habit has already formed (and he's not the only one on here with that habit. You'll find no shortage of "wannabe-Einsteins" trying to get some validation for their "theories". Though what posssible validation one could get from posters on a comment section of a site about PR reports ABOUT scientfic papers is beyond me)
Phys1
5 / 5 (5) Feb 04, 2016
I don't want to be a bore, but this is about the best science anyone can do.
It looks extremely silly if you criticise this and are so obviously not qualified.
Much worse, someone could read your post and actually believe it.
Do you realise that would harm science, our culture and our wealth?
Be responsible.
Phys1
5 / 5 (4) Feb 04, 2016
@KBK
It irritates that you criticise excellent work without understanding the fundamentals.
Don't make it a habit.

Unfortunately the guy has been around for quite some years, The habit has already formed (and he's not the only one on here with that habit. You'll find no shortage of "wannabe-Einsteins" trying to get some validation for their "theories". Though what posssible validation one could get from posters on a comment section of a site about PR reports ABOUT scientfic papers is beyond me)

So a candidate for my list.
I will give him the opportunity to repent, now ;-) . We all make mistakes.
Hyperfuzzy
1 / 5 (1) Feb 04, 2016
The response from the perspective of an electron, the field appears at each instance as a particle of charge located at a distance in the direction of the Poynting vector, a 4D vector, definition pending!
Hyperfuzzy
1 / 5 (1) Feb 04, 2016
By the way, the particle motion is embedded in the field, i.e. particle->field, i.e. the field carries the velocity vector of the charge. Just add it to the normal, piece of cake.
Hyperfuzzy
1 / 5 (1) Feb 04, 2016
So response? Isn't that the wave-let created or defined by motion, relative to a single point, i.e the response! Don't get the question. Don't we know this!

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