Institut des Sciences Moléculaires d'Orsay




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Home > Research Teams > Dynamics and Interactions: Radiation, Atoms and Molecules (DIRAM)

Dynamics and Interactions: Radiation, Atoms and Molecules (DIRAM)

The DIRAM group currently gathers 9 permanent researchers and 5 PhD students, both experimentalists and theoreticians. Its research activity focuses on the investigation of fundamental processes and related dynamics in the interaction of radiation with matter.

The processes, which are investigated, cover radiation-induced excitation, ionization and / or dissociation in atoms, ions or molecules, primarily in gas phase and in various irradiation regimes. In particular the interaction with intense (10 to 100 TW/cm2, 1TW = 1012W) and ultrashort (femtoseconds to attoseconds, 1 as = 10-18 s) laser pulses provides access to fundamental mechanisms used in the interpretation and control of the dynamics of electrons and nuclei. These fundamental studies are important for many applications, among which molecular imaging techniques, or the production of new laser sources.

Collective effects, correlations and the role of the environment on the dynamics of various fundamental quantum systems are also part of our current research on nano-physics, quantum optics and quantum information.

Radiation in the X-ray and XUV range are the core of our experimental studies, which are performed at specific user facilities such as the SOLEIL-synchrotron facility, the high-order harmonic sources of CEA-Saclay, the plasma-based XUV lasers of LASERIX and LOA, or the X free-electron laser (FEL) facilities (such as FERMI-Elettra in Italy). These experiments are based on innovative methods and advanced (often unique) instruments, which are used to extract accurate data on fundamental processes, such as: coincidence momentum spectroscopy for the study of molecular dissociative photoionization or multiple photoionization, ECR (electron cyclotron resonance) ion sources for the measurement of absolute photoionization cross sections in multiply charged ions, XUV interferometry for the study of the spectro-temporal properties of XUV lasers.

At the theoretical level, our research uses both quantum mechanical time-dependent and independent techniques, including methods for Floquet resonance calculations, wave packet propagations and the resolution of coupled Maxwell-Schrödinger or Maxwell-Liouville equations.

Our work involves a number of collaborations with other laboratories in France and abroad. We are involved in several national and European scientific networks such as Laserlab Europe, GDRI XFEL-Science, ITN CORINF, as well as in several projects funded by Paris-Saclay University (OPT2X, ATTOLab and CILEX).

Dynamique ultra-rapide électron-noyaux sondée par photoionisation des molécules

L’irradiation d’une molécule par un rayonnement XUV induit une excitation électronique à l’origine d’un ensemble de processus, éventuellement couplés entre eux, incluant l’ionisation (éjection d’un ou de plusieurs électrons), la propagation de paquets d’onde électroniques (migration de charge), ou la mise en mouvement des noyaux (paquets d’onde vibrationnel ou rotationnel, dissociation), qui constituent autant d’étapes intervenant dans la compréhension des mécanismes et le contrôle des réactions chimiques.

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Photoionisation of atomic and molecular ions

The activity of this group is based on the study of photoionization processes, in the XUV photon energy range, in various ionic species (atomic multiply-charged ions, molecular ions…). The measurements of the physical parameters which characterized these processes (absolute photoionization cross sections, excitation energies…), performed at the SOLEIL synchrotron radiation facility, are compared to the theoretical predictions obtained from various models. This comparison, done in close collaboration with several groups of theoreticians, enables the improvement of the quantum mechanics models developed for the modeling of astrophysical plasmas (interstellar medium, planetary atmospheres…) and laboratory plasmas (laser produced plasmas, tokamak…).

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Propriétés spectrales et temporelles des lasers XUV générés par plasma

Les plasmas chauds et denses, générés par des lasers de forte puissance ou des décharges électriques très rapides, peuvent être utilisés pour générer un faisceau laser à courte longueur d’onde dans le domaine XUV (longueur d’onde 2 - 50 nm). L’inversion de population, nécessaire à l’effet laser, est produite entre deux niveaux excités de certains ions fortement chargés (par exemple Mo14+), sous l’effet des collisions avec les électrons libres. L’effet laser démarre à partir de l’émission spontanée, qui est ensuite fortement amplifiée par émission stimulée, conduisant à l’émission d’un faisceau laser XUV intense, collimaté et extrêmement monochromatique.

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Coherence and control of quantum processes

The production of ultra-short optical pulses has opened an exciting new chapter for the study of atomic and molecular dynamics. It is now possible to generate laser pulses with a duration ranging from a few tens of attoseconds to a few tens of femtoseconds and whose spectral content, phase distribution and temporal envelope can be controlled experimentally.

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Intense laser controlled molecular processes: Electronic and nuclear dynamics

Short intense laser pulses produce strong internal distortions in molecules, inducing thus selective dynamical effects both at the electronic and nuclear level, which can be exploited for imaging purposes or in designating control strategies.

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Cold Matter and quantum information

Entanglement is a fundamental property of quantum systems defined as the non separability of the quantum states describing a many body system. It displays intriguing non-local properties at the heart of an intense debate since the early days of the quantum theory. Despite its fundamental interest and importance for applications, detecting and quantifying entanglement remains a challenge for both theoreticians and experimentalists.

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