This forms an essential basis for electron holography of atoms (Physical Review Letters 103, 053001).
Ionization of helium in an ultra-short laser pulse. The electron is launched from the atomic potential (blue funnel) at t1 or t2, i. e. at the maxima of the electric field amplitude (yellow curve). Both paths sample the parent ion differently. The corre-sponding wave packets of the escaping electron are finally superimposed (right) leading to interference.
MPI für Kernphysik
Calculated interference pattern of a single electron following ionization of helium in an ultra-short laser pulse. The figure shows the velocity distribution parallel (horizontal axis) and perpendicular (vertical axis) to the laser polarization direction.
MPI für Kernphysik
How do electrons move inside an atom and what happens in detail if this motion is distorted? Capturing this dynamics in time-dependent quantum systems in detail is the great dream of physicists - and has become more and more reality during recent years through substantially advanced experimental methods.
Attosecond physics provides a new promising approach with a precision better than a millionth of a billionth second, just the timescale of a moving electron inside an atom. In order to get a deeper insight into the electron cloud, Max Planck researchers utilize the electron's ability to interfere with itself due to its quantum wave nature. Interference is also the basis of optical holography: here, a beam splitter directs light waves on two paths, and one of them illuminates the object to be investigated. The reflected light is then superimposed with the direct beam creating an interference pattern which contains complete information about the sample and allows its reconstruction.
In the current experiment the helium atom itself plays the role of the beam splitter being exposed to a few-cycle laser pulse: the electron can only be pulled out of the atom by the laser field within a very short time interval, i.e. if the amplitude of the os-cillating field has reached a maximum. In case of the sine-type evolution of the elec-trical field used in the experiment (see Fig. 1) one finds exactly two ionization times t1 and t2. An electron launched at t1 is forced by the oscillating field to turn back and pass its parent ion before it finally leaves the atom. During the passage the electronic wave packet picks up information about the parent ion's internal structure. Being launched at t2 the electron escapes directly without detour (Abb 1). If the electron's direction and velocity is finally identical and, thus, both possible quantum paths indis-tinguishable, interference occurs like in the well-known double-slit experiment (Abb. 1). Akin to optical holography the parent ion consisting of the nucleus and the resid-ual second electron is scanned by the first wave packet whereas the electron launched at t2 forms the reference beam.
The electrons are recorded by a 'reaction microscope' developed and built at the MPI and installed at the AS-1 beam line at MPQ for the joint experiment. Linearly-polarized ultra-short (5 fs) laser pulses at 740 nm are generated with a repetition rate of 3 kHz and focused in an ultrahigh vacuum chamber onto a supersonic helium gas jet. The reaction products - electrons and helium ions - are directed towards two detectors by means of weak electric and magnetic fields. The direction and velocity of the particles is derived from their time of flight and position on the detector. The physicists compared the velocity distributions measured as described above with results of a theoretical model calculation (Abb. 2) by Dieter Bauer (MPIK). The data agree qualitatively very well, although the model does not include the full complex-ity of the helium atom. Hence, the researchers conclude that the observed interfer-ence pattern was indeed generated by a true two-slit arrangement. The slits are de-termined by the two time windows where the electron can be launched. It follows from the observed pattern that the effective width of the slits amounts only to 20 at-toseconds. Thus, the electron's three-dimensional velocity distribution, obtained by means of the reaction microscope, comprising the interference pattern could be envisaged as a time-dependent hologram of the helium ion.
The fellow researchers of Ullrich and Kling ascribe a large potential to this method, to gain further advancement in imaging the inner dynamics of atoms and more de-tailed time-resolved information about atomic and molecular structure. A better control of the laser pulse shape could for instance resolve variations in the electron cloud of the atom's ionic core on an attosecond time scale.
Contact:Prof. Dr. Joachim Ullrich
http://www.mpi-hd.mpg.de/keitel/dbauer/ Website of the Bauer Group (MPIK)
Dr. Bernold Feuerstein | Max-Planck-Institut
Witnessing turbulent motion in the atmosphere of a distant star
23.08.2017 | Max-Planck-Institut für Radioastronomie
Heating quantum matter: A novel view on topology
22.08.2017 | Université libre de Bruxelles
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
23.08.2017 | Life Sciences
23.08.2017 | Life Sciences
23.08.2017 | Physics and Astronomy