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Nobel Physicists Lay Attosecond Groundwork for Quantum Discovery

In 1994, Agostini and his group studied the
Laser light interacts frequency-modulation principle in a two-color
with atoms in a gas photon field. This principle was subsequently
Experiments that created overtones in laser developed into a metrology technique dubbed
light led to the discovery of the mechansim
that causes them. How does it work? RABBIT (an approximate abbreviation of
“reconstruction of attosecond beating by
ENERGY LEVEL interference of two-photon transitions”). By
LASER LIGHT
focusing the extreme-ultraviolet pulse and
light from the drive laser onto a rare gas target
ATOM’S FIELD
and analyzing the photoelectrons emanating
ELECTRON
TUNNELING from the target, the RABBIT technique made
it possible to measure the pulse duration of a
train of attosecond pulses (Figure 3).
NUCLEUS
Agostini and his team combined the “pulse
train” with a delayed portion of the original
1 An electron that is bound to 2 The atom’s field is 3 The free electron is still 4 To reattach to the atom’s nucleus, laser pulse to determine the phase relation-
the electron must rid itself of the
an atom’s nucleus cannot
distorted when it is
affected by the laser
normally leave its atom; it affected by the laser field and gains some extra energy it gained during its
does not have enough energy pulse. When the electron extra energy. When the journey. This is emitted as an ship between the harmonics. This procedure
to lift itself out of the well is only held by a narrow field turns and changes ultraviolet flash, the wavelength of also provided a measurement for the duration
created by the atom’s barrier, quantum direction, the electron is which is linked to that of the laser
electrical field. mechanics allow it to pulled back in the field, and differs depending on how of the train’s pulses, revealing that each pulse
tunnel out and escape. direction it came from. far the electron moved.
lasted a specific number of attoseconds.
©Johan Jarnestad/The Royal Swedish Academy of Sciences In 2001, research teams operating at CEA
Paris-Saclay and the Vienna University of
Figure 2: Overtone generation process Technology demonstrated attosecond pulses.
1
(Source: Johan Jarnestad/Royal Swedish Academy of Sciences ) The Agostini group at CEA Paris-Saclay
generated a series of pulses with a duration of
ing effect. Because the electric field produced and explained from a quantum perspective. 250 attoseconds, as measured by the RABBIT
by the laser pulses oscillates, when it reverses Utilizing quantum mechanics, the researchers metrology with argon as the target gas. At the
direction, the free electron can return to the accurately predicted the general shape of the Vienna University of Technology, the Krausz
nucleus of the atom (Figure 2). This process HHG spectrum by calculating the different group produced 650 attosecond-long isolated
emits electromagnetic radiation of a much intensities of the various overtones. As soon as pulses. These accomplishments paved the way
higher frequency (and therefore a much they realized which harmonics to expect, they for the study of electron dynamics in atoms,
smaller period, or duration) than the laser devised techniques to combine them to create molecules and condensed matter.
radiation used to trigger the process itself. a new wave with attosecond-scale peaks.
The high-order harmonics generation (HHG) Following on this work, Agostini and WHY ARE ATTOSECONDS SO IMPORTANT?
process, demonstrated in experiments con- Krausz were able to generate shorter light With the Nobel laureates’ experiments in atto-
ducted by L’Huillier’s group, was later analyzed pulses than had been achieved previously. second physics having laid the groundwork,
it is now possible for researchers to analyze
and study the dynamics and time evolution of
many processes in quantum mechanics, such
The world of electrons is explored Figure 3: as chemistry and materials science.
with the shortest of light pulses Setup for
When laser light is transmitted through a gas, ultraviolet According to L’Huillier, prerequisites for
overtones arise from the atoms in the gas. In the right Agostini’s
conditions, these overtones may be in phase. When their the study of attosecond phenomena are a
cycles coincide, concentrated attosecond pulses are formed.
experiment cutting-edge, ultrafast laser system, advanced
OVERTONES ARE involving the attosecond engineering and a robust applica-
SUPERIMPOSED
splitting and tion program. 2
recomposing To meet the challenging requirements of
of laser beams attosecond science, an attosecond source
REINFORCE OR CANCEL
EACH OTHER (Source: Johan must be created using both specialized ultra-
Jarnestad/Royal fast laser technology and attosecond physics.
Swedish Academy of From there, the technology can be used to
ATTOSECOND PULSES 1
Sciences ) investigate potential uses in numerous fields,
including but not limited to atomic and
Example of an molecular physics, surface physics, plasmon-
experimental ics and ultrafast coherent imaging. ■
setup PULSE COMBINED
TRAIN
BEAM OBSERVATION
FILTER e- REFERENCES
DELAY
GAS 1 The Nobel Prize in Physics 2023. (Oct. 3, 2023).
“Experiments with light capture the shortest of
LASER LIGHT moments.” Royal Swedish Academy of Sciences.
tinyurl.com/4hhbp7db
The laser light is divided into two beams, where one is 2 tinyurl.com/23s93j2w
used to create a train of attosecond pulses. This pulse
train is then added to the original laser pulse and the
combination is used to perform extremely rapid
experiments.
Stefano Lovati is a contributing writer for
©Johan Jarnestad/The Royal Swedish Academy of Sciences
EE Times Europe.
www.eetimes.eu | NOVEMBER 2023