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PhD subjects

6 sujets IRAMIS

Dernière mise à jour : 13-12-2018


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• Radiation-matter interactions

 

Irradiation effects on the infrared optical properties of ZnGeP2

SL-DRF-19-0056

Research field : Radiation-matter interactions
Location :

Laboratoire des Solides Irradiés

Laboratoire des Solides Irradiés

Saclay

Contact :

Jérémie Lefevre

Bruno BOIZOT

Starting date : 01-10-2019

Contact :

Jérémie Lefevre

Ecole Polytechnique - Laboratoire des Solides Irradiés

01 69 33 45 30

Thesis supervisor :

Bruno BOIZOT

CEA - DRF/IRAMIS/LSI/LSI

01 69 33 45 22

Personal web page : https://www.polytechnique.edu/annuaire/fr/users/bruno.boizot

Laboratory link : https://portail.polytechnique.edu/lsi/fr/recherche/defauts-desordre-et-structuration-de-la-matiere

The ZnGeP2 compound, in its monocrystalline form, is a remarkable and very promising material for infrared optical applications: it is transparent between 1 and 8 µm and, due to its positive birefringence, it has highly-effective nonlinear optical properties.



The improvement of transparency properties in the infra-red (IR) domain of this material is thus both a scientific and technical challenge. However, defects coming from the synthesis processes induce absorption bands in the IR range, thus limiting the physical properties of this compound. Irradiation could be a new way for changing the nature and the content of defects responsible of this absorption in the IR domain.



The goal of the PhD is therefore to define the irradiation conditions (fluences, beam energy, irradiation temperature ...) for improving the IR properties of irradiated ZnGeP2. For that purpose, a quantitative spectroscopic tool like Electron Paramagnetic Resonance spectroscopy will be used in order to determine the mechanisms of irradiation defects production and their interactions with the defects produced during the pulling of ZnGeP2 crystals.

Physics and applications of hot electrons of plasmonic origin

SL-DRF-19-0347

Research field : Radiation-matter interactions
Location :

Service de Physique de l'Etat Condensé

Laboratoire d'Electronique et nanoPhotonique Organique

Saclay

Contact :

Ludovic DOUILLARD

Starting date : 01-10-2019

Contact :

Ludovic DOUILLARD

CEA - DRF/IRAMIS/SPEC/LEPO

01 69 08 36 26

Thesis supervisor :

Ludovic DOUILLARD

CEA - DRF/IRAMIS/SPEC/LEPO

01 69 08 36 26

Personal web page : http://iramis.cea.fr/Pisp/ludovic.douillard/

Laboratory link : http://iramis.cea.fr/spec/LEPO/

At small scale, the interaction of light with a metallic object results in the occurrence of remarkable resonances within the absorption spectrum, the plasmon resonances. These resonances correspond to collective oscillations of the charge carriers [Mie 1908] and constitute a research domain in itself known as Plasmonics. Beyond its interest in the manipulation of the near optical field, a metal object at plasmonic resonance is a source of hot electrons whose electronic properties can be used to achieve non classical chemistry reactions at the local scale.



This work aims to study the fundamental physics of the emission of hot electrons by a nanometric metallic object in connection with applications, particularly medical ones such as the anticancer photodynamic therapies. It is a work of experimental character in close collaboration to a relevant partnership of physicists, chemists, biologists and oncologists from different Institutions (CEA, CentraleSupélec, Hospital Saint-Louis). It will benefit from the experience acquired by the CEA IRAMIS SPEC group in LEEM / PEEM (Low Energy Electron / PhotoEmission Electron) microscopies, the principle of which is based directly on the acquisition of the distribution of the photoelectrons emitted in response to a plasmon resonance decay [Douillard 2017, 2012, 2011] and is therefore a unique technique of choice for this study.



The objectives are to answer fundamental questions related to the emission of hot electrons by a metallic particle under ultrafast multiphoton optical excitation. In particular, this involves determining the emission dynamics of the charge carriers (pump probe experiment) and their physical distributions: spatial mapping of the emission hot spots at the nano-object scale and energy mapping through the determination of the kinetic energy spectra. The ultimate goal takes place in the context of a project devoted to medical oncology (breast cancer) and more specifically on the optimization of anticancer therapies under development, namely the photothermal and photodynamic therapies.



Keywords: hot electrons, plasmon, laser, PEEM, LEEM

Quantum fragmentation in frustrated magnets

SL-DRF-19-0538

Research field : Radiation-matter interactions
Location :

Laboratoire Léon Brillouin

Groupe 3 Axes

Saclay

Contact :

SYLVAIN PETIT

ELSA LHOTEL

Starting date : 01-10-2018

Contact :

SYLVAIN PETIT

CEA - DRF/IRAMIS

01 69 08 60 39

Thesis supervisor :

ELSA LHOTEL

CNRS - Insitut Néel

04 76 88 12 63

Personal web page : http://iramis.cea.fr/Phocea/Membres/Annuaire/index.php?uid=spetit

Laboratory link : http://www-llb.cea.fr/

Magnetic frustration is one of the modern routes in condensed matter physics leading to the discovery of new states of matter. The “spin ice” and more generally, the “Coulomb phases” are celebrated examples of this physics. In contrast with classical magnetically ordered phases, these states remain disordered down to the lowest temperatures, yet form a correlated paramagnet with specific spin-spin correlations. In this context, a new concept has been recently proposed, called “magnetic fragmentation” [PRX 4, 011007 (2014)]. This is an original state where the magnetic moment fragments into two sub-fragments: one of them forms an antiferromagnetic phase with a reduced ordered moment, while the other keeps fluctuating and forms a Coulomb phase.



In combining magnetization measurements, elastic and inelastic neutron scattering experiments, we have shown that the pyrochlore compound Nd2Zr2O7 could be a realization of this theory [1,2], even if experimental evidences suggest that still not understood quantum phenomena are at play.



This thesis work aims at understanding the origin of fragmentation in this system. We especially plan to determine its stability range by studying doped samples. Actually, replacing part of the Zirconium (Zr) by Titanium (Ti), or Neodymium (Nd) by Lanthanum (La), magnetic interactions can be modified. Varying the substitution, we will explore the phase diagram and probe the possible existence of a quantum critical point predicted by theory. The complementarity between macroscopic and neutron scattering measurements is one of the key points to determine the quantum Hamiltonian and beyond, understand the microscopic mechanisms of magnetic fragmentation, along with the nature of the spin dynamics that emerge from this peculiar ground state.



The thesis work will take place in France both at the Institut Néel (Grenoble) and at LLB (Saclay). It consists in measuring both the magnetization and specific heat down to base temperature (100 mK) (Institut Néel) and to finely determine the magnetic structures as well as the spin excitations spectrum by the different neutron techniques. The latter will be carried out at LLB (Saclay) and at ILL (Grenoble). A large part of the data analysis will be based on numerical simulation tools. Most of them exist today but may be further developed.

Attosecond pulses generated in activeoptical gratings: experiments, theory and applications

SL-DRF-19-0487

Research field : Radiation-matter interactions
Location :

Service Laboratoire Interactions, Dynamique et Lasers

Attophysique

Saclay

Contact :

Thierry Ruchon

Starting date : 01-10-2019

Contact :

Thierry Ruchon

CEA - DRF/IRAMIS/LIDyL/ATTO

0169087010

Thesis supervisor :

Thierry Ruchon

CEA - DRF/IRAMIS/LIDyL/ATTO

0169087010

Personal web page : http://iramis.cea.fr/LIDYL/Pisp/thierry.ruchon/

Laboratory link : http://iramis.cea.fr/LIDYL/atto/

Light in the extreme ultraviolet (XUV) is a universal probe of mater, may it be in diluted or condensed phase: photons associated with this spectral range carry energy of 10 to 100 eV, sufficient to directly ionize atoms, molecules or solids. Large scale instruments such as synchrotrons or the lately developed free electron lasers (FEL) work in this spectral range and are used to both study fundamental light matter interaction and develop diagnosis tools. However these instruments do not offer the temporal resolution require to study light matter interactions at their ultimate timescales, which is in the attosecond range (1as = 10-18s). An alternative is offered by the recent development of XUV sources based on high order harmonic generation (HHG). They are based on the extremely nonlinear interaction of a femtosecond intense laser beam with a gas target. Our laboratory has pioneered the development, control and design of these sources providing XUV attosecond pulses.



During this PhD project, we will develop specific setups putting at play two beams forming an active grating to generate attosecond pulses with controlled angular momenta, may it be spin or orbital angular momenta. This will open new applications roads through the observations of currently ignored spectroscopic signatures. On the one hand, the fundamental aspects of the coupling of spin and orbital angular momentum of light in the highly nonlinear regime will be investigated, and on the other hand, we will tack attosecond novel spectroscopies, may it be in diluted or condensed phase. In particular, we will chase helical dichroism, which manifest as different absorptions of beams carrying opposite orbital angular moments. These effects are largely ignored to date.

The student will acquire practical knowledge about lasers, in particular femtosecond lasers, and hands on spectrometric techniques of charged particles. He/she will also study strong field physical processes which form the basis for high harmonic generation. He/she will become an expert in attosecond physics. The acquisition of analysis skills, computer controlled experiments skills will be encouraged although not required.



Detailed presentation of the subject : http://iramis.cea.fr/LIDYL/Pisp/thierry.ruchon/

Plasma Mirrors 'on-chip': "Towards extreme intensity light sources and compact particle accelerators"

SL-DRF-19-0633

Research field : Radiation-matter interactions
Location :

Service Laboratoire Interactions, Dynamique et Lasers

Physique à Haute Intensité

Saclay

Contact :

Henri VINCENTI

Guy BONNAUD

Starting date : 01-10-2019

Contact :

Henri VINCENTI

CEA - DRF/IRAMIS/LIDyL/PHI

0169080376

Thesis supervisor :

Guy BONNAUD

CEA - DRF/IRAMIS/LIDyL/PHI

0169088140

Personal web page : http://iramis.cea.fr/Pisp/henri.vincenti/

Laboratory link : http://iramis.cea.fr/LIDYL/PHI/

More : https://picsar.net

SL-DRF-19-0432

Research field : Radiation-matter interactions
Location :

Service Nanosciences et Innovation pour les Materiaux, la Biomédecine et l'Energie

Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire

Saclay

Contact :

Marie GELEOC

Jean-Philippe RENAULT

Starting date : 01-09-2019

Contact :

Marie GELEOC

CEA - DRF/IRAMIS/LIDyL/SBM

Thesis supervisor :

Jean-Philippe RENAULT

CEA - DRF/IRAMIS/NIMBE/LIONS

01 69 08 15 50

Personal web page : http://iramis.cea.fr/Pisp/marie.geleoc/

Laboratory link : http://iramis.cea.fr/lidyl/sbm/

More : http://iramis.cea.fr/Phocea/Membres/Annuaire/index.php?uid=jrenault

 

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