- Jan 27, 2020
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Hayseed, the following article may be of note to you:
It has always been impossible to clearly photograph electrons since their extremely high velocities have produced blurry pictures. In order to capture these rapid events, extremely short flashes of light are necessary, but such flashes had never been available before.
Using a newly developed technology for generating short pulses from intense laser light, called attosecond pulses, scientists at the Lund University Faculty of Engineering in Sweden have managed to capture the electron in motion for the first time.
The movie shows how an electron rides on a light wave after just having been pulled away from an atom. This is the first time an electron has ever been filmed, and the results are presented in the latest issue of Physical Review Letters.
Experimental results obtained in helium at an intensity of 1:2 1013 W=cm2 are shown. The results are
distinctively different from those taken in argon (Fig. 1).With this higher intensity, more momentum is transferred to the electrons, and in combination with the lower initial energy, some electrons return to the atomic potential for further interaction. In the first panel, we compare the experimental results (right) with theoretical calculations (left) obtained for the same conditions. The excellent agreement is the strongest evidence for coherent scattering effects in the experiment. All the substructures are well reproduced except for the highly saturated innermost peak in the experiment, which most likely is due to above threshold ionization of residual water in the experimental chamber.
“It takes about 150 attoseconds for an electron to circle the nucleus of an atom. An attosecond is 10^-18 seconds long, or, expressed in another way: an attosecond is related to a second as a second is related to the age of the universe,” says Johan Mauritsson, an assistant professor in atomic physics at the Faculty of Engineering, Lund University. He is one of seven researchers behind the study, which was directed by him and Professor Anne L’Huillier.
With the aid of another laser these scientists have moreover succeeded in guiding the motion of the electron so that they can capture a collision between an electron and an atom on film.
“We have long been promising the research community that we will be able to use attosecond pulses to film electron motion. Now that we have succeeded, we can study how electrons behave when they collide with various objects, for example. The images can function as corroboration of our theories,” explains Johan Mauritsson.
These scientists also hope to find out more about what happens with the rest of the atom when an inner electron leaves it, for instance how and when the other electrons fill in the gap that is created.
“What we are doing is pure basic research. If there happen to be future applications, they will have to be seen as a bonus,” adds Johan Mauritsson.
The length of the film corresponds to a single oscillation of the light, but the speed has then been ratcheted down considerably so that we can watch it. The filmed sequence shows the energy distribution of the electron and is therefore not a film in the usual sense.
“By taking several pictures of exactly the same moment in the process, it’s possible to create stronger, but still sharp, images. A precondition is for the process to be repeated in an identical manner, which is the case regarding the movement of an electron in a ray of light. We started with a so-called stroboscope. A stroboscope enables us to ‘freeze’ a periodic movement, like capturing a hummingbird flapping its wings. You then take several pictures when the wings are in the same position, such as at the top, and the picture will turn out clear, despite the rapid motion,” clarifies Johan Mauritsson.
Coherent Electron Scattering Captured By an Attosecond Quantum Stroboscope, J. Mauritsson, P. Johnsson, E. Mansten, M. Swoboda, T. Ruchon, A. L´Huillier, and K. J. Schafer, Phys. Rev. Lett. 100, 073003, (issue of 22 February)
See:
View: https://www.youtube.com/watch?v=ofp-OHIq6Wo
See: https://www.science20.com/news_releases/electron_caught_on_film_for_the_first_time
Previously scientists have only been able to study the movements of electrons using indirect methods, like measuring their spectrum. In this process, not only has it been possible to measure the resulting movement of an electron, but now we have the opportunity to monitor the entire sub-atomic event.
Attosecond pulses have been used for a number of years, but Swedish scientists have just managed to use them to film electron movements now, because attosecond pulses themselves are usually too weak to take clear pictures.
The foregoing complicated process reminds me of the operation of the Molecular Beam Epitaxy, or MBE, where the growth process involves controlling, via shutters and source temperature, molecular, and/or laser beams directed at a single crystal sample so as to achieve epitaxial growth. The beams impinge unreacted on the sample with a cryoshroud cooled by liquid nitrogen. Reactions take place predominantly on the sample surface where the source beams are incorporated into the growing film.
In any case, bravo to those who have filmed a moving electron. Again, the smallest particles are being illuminated while the largest bodies in our universe are finally being understood. Einstein, Bethe, Dirac, and so many other giants are smiling.
Hartmann352
It has always been impossible to clearly photograph electrons since their extremely high velocities have produced blurry pictures. In order to capture these rapid events, extremely short flashes of light are necessary, but such flashes had never been available before.
Using a newly developed technology for generating short pulses from intense laser light, called attosecond pulses, scientists at the Lund University Faculty of Engineering in Sweden have managed to capture the electron in motion for the first time.
The movie shows how an electron rides on a light wave after just having been pulled away from an atom. This is the first time an electron has ever been filmed, and the results are presented in the latest issue of Physical Review Letters.
Experimental results obtained in helium at an intensity of 1:2 1013 W=cm2 are shown. The results are
distinctively different from those taken in argon (Fig. 1).With this higher intensity, more momentum is transferred to the electrons, and in combination with the lower initial energy, some electrons return to the atomic potential for further interaction. In the first panel, we compare the experimental results (right) with theoretical calculations (left) obtained for the same conditions. The excellent agreement is the strongest evidence for coherent scattering effects in the experiment. All the substructures are well reproduced except for the highly saturated innermost peak in the experiment, which most likely is due to above threshold ionization of residual water in the experimental chamber.
“It takes about 150 attoseconds for an electron to circle the nucleus of an atom. An attosecond is 10^-18 seconds long, or, expressed in another way: an attosecond is related to a second as a second is related to the age of the universe,” says Johan Mauritsson, an assistant professor in atomic physics at the Faculty of Engineering, Lund University. He is one of seven researchers behind the study, which was directed by him and Professor Anne L’Huillier.
With the aid of another laser these scientists have moreover succeeded in guiding the motion of the electron so that they can capture a collision between an electron and an atom on film.
“We have long been promising the research community that we will be able to use attosecond pulses to film electron motion. Now that we have succeeded, we can study how electrons behave when they collide with various objects, for example. The images can function as corroboration of our theories,” explains Johan Mauritsson.
These scientists also hope to find out more about what happens with the rest of the atom when an inner electron leaves it, for instance how and when the other electrons fill in the gap that is created.
“What we are doing is pure basic research. If there happen to be future applications, they will have to be seen as a bonus,” adds Johan Mauritsson.
The length of the film corresponds to a single oscillation of the light, but the speed has then been ratcheted down considerably so that we can watch it. The filmed sequence shows the energy distribution of the electron and is therefore not a film in the usual sense.
“By taking several pictures of exactly the same moment in the process, it’s possible to create stronger, but still sharp, images. A precondition is for the process to be repeated in an identical manner, which is the case regarding the movement of an electron in a ray of light. We started with a so-called stroboscope. A stroboscope enables us to ‘freeze’ a periodic movement, like capturing a hummingbird flapping its wings. You then take several pictures when the wings are in the same position, such as at the top, and the picture will turn out clear, despite the rapid motion,” clarifies Johan Mauritsson.
Coherent Electron Scattering Captured By an Attosecond Quantum Stroboscope, J. Mauritsson, P. Johnsson, E. Mansten, M. Swoboda, T. Ruchon, A. L´Huillier, and K. J. Schafer, Phys. Rev. Lett. 100, 073003, (issue of 22 February)
See:
See: https://www.science20.com/news_releases/electron_caught_on_film_for_the_first_time
Previously scientists have only been able to study the movements of electrons using indirect methods, like measuring their spectrum. In this process, not only has it been possible to measure the resulting movement of an electron, but now we have the opportunity to monitor the entire sub-atomic event.
Attosecond pulses have been used for a number of years, but Swedish scientists have just managed to use them to film electron movements now, because attosecond pulses themselves are usually too weak to take clear pictures.
The foregoing complicated process reminds me of the operation of the Molecular Beam Epitaxy, or MBE, where the growth process involves controlling, via shutters and source temperature, molecular, and/or laser beams directed at a single crystal sample so as to achieve epitaxial growth. The beams impinge unreacted on the sample with a cryoshroud cooled by liquid nitrogen. Reactions take place predominantly on the sample surface where the source beams are incorporated into the growing film.
In any case, bravo to those who have filmed a moving electron. Again, the smallest particles are being illuminated while the largest bodies in our universe are finally being understood. Einstein, Bethe, Dirac, and so many other giants are smiling.
Hartmann352
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