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Researchers of the Groupe
Matière Condensée et Matériaux (Materials and Condensed
Matter Group, CNRS – Université Rennes 1), in partnership
with the ESRF(1) , have succeeded in filming, at ten
billionths of a second, the ordering of molecules in a material during
induced laser switching, with the help of x-rays. In addition to the x-ray
absorption process used in medical radiography, the diffraction(2)
of x-rays makes it possible to know the spatial structure between atoms
and molecules. Registering this information on a time scale of 100 picoseconds(3)
should lead to major advances in controlling the manipulation of molecules
in a material by a flash of light. This research is published in the journal,
Science, of April 25, 2003.
The observation of the movement
of atoms during the transformation of matter has been an inaccessible
dream for a long time. It is now within our reach thanks to the diffraction
of ultra-short x-ray pulses at the ESRF, making it possible to capture
atomic or molecular movements at time scales of one hundredth of a picosecond
and, eventually, one hundredth of a femtosecond(4) .
It is with this type of technique developed on the European Synchrotron
in Grenoble, France, that the team of the Materials and Condensed Matter
Group and the team of the ESRF studied the transformation of the photo-induced
phase of a charge-transfer molecular material, with a time resolution
of 100 ps. In this material, a laser pulse can induce a new electronic
and structural order on a large scale: each unit of laser light (photon)
can transform several hundred molecules between a neutral state and an
ionic state by an electronic change. This illustrates the advantage of
advanced molecular materials in relation to more traditional materials
such as kitchen salt (Na+Cl-) in which the photo-induced electron change
can only take place locally. Researchers were able to observe how photo-excited
state molecules choose a new special order in a transition state that
could only be captured with the help of x-rays. This performance was only
made possible by pooling the know-how of different teams of physicists
and chemists from several different countries (France, Japan, Poland and
Germany).
Manipulating matter with laser light is a particularly "exciting"
technological and scientific goal. It is absolutely necessary to understand
the ultra-rapid mechanisms that make it possible for a light pulse to
cause a material to switch between two different physical states (optical,
electrical, magnetic, etc.). In other words, this means controlling the
way in which molecules move within a coherent process and not in an independent
and chaotic manner.
(1)European
Synchrotron Radiation Facility, Grenoble, France.
(2)Coherent
reflection by a large population of atoms, almost perfectly ordered.
(3)1ps=10-12
s
(4)1fs=10-15
s
Researcher
contact:
Eric Collet
Groupe Matière Condensée et Matériaux
Tel: +33 2 23 23 65 32
e-mail: eric.collet@univ-rennes1.fr
Press contact:
Muriel Ilous
Tel: +33 1 44 96 43 09
e-mail: muriel.ilous@cnrs-dir.fr
Contact – Mathematical and Physical Sciences Department:
Frédérique Laubenheimer
Tel: +33 1 44 96 42 63
e-mail: frederique.laubenheimer@cnrs-dir.fr
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