Theoretical and experimental studies of the polarized light's propagation into OLED structure
In collaboration with chemists from CEA Saclay and the University of Rennes, Leti's LCEM laboratory is interested in new chiral molecules for OLED (Organic Light Emitting Device) sources able to emit circularly polarized light (CP). The interest of these CPOLED sources is multiple and encompasses both micro-screens and healthcare applications. While the state of the art is quite extensive on the chemical part, few studies have looked at the generation and transport of light in CPOLEDs components.Likewise, the conditions for measuring the polarity of the light emitted are not very detailed in the existing literature.
At the LCEM laboratory, where these chiral molecules are integrated into CPOLED devices, the goal is to design OLED architectures that can better preserve the polarization of light. To do this, it is essential to understand the propagation of light in OLED stacks from a theoretical and experimental point of view. This work is part of a larger collaboration set up in the ANR "i-chiralight" project.
In this context, we are proposing a study which will take place in two phases.
- Study of simple emitting materials: The materials to be studied will be thin layers deposited under vacuum using evaporation's system of thin layers available in the laboratory. The organic materials used will be supplied by our chemical partners in Saclay or Rennes. Optical characterizations such as ellipsometry,photoluminescence, etc. will be carried out in order to assess the performance of molecules in terms of emission efficiency but also in terms of the rotational power of light. For this last point, a model able to calculate all the terms of the Müller matrices is under development and the validation of this one will be a work to be carried out by the post-doctoral fellow.
- Study of complete OLED components: In the second phase of this work, we will focus on the complete OLED system by studying the propagation of optical modes in the stack of the different layers const
Dynamic monitoring by light scattering of mass transfer between two phases in multiphase flows
The understanding and the modeling of recycling processes studied at CEA, require the measurement of both local and average properties of multiphase flows involved in chemical engineering devices. Moreover, as the R&D studies are generally conducted on small-scale experiments, access to these quantities is often difficult, especially considering that measurement methods should not disturb the observed system. In this context, optical methods, associated to extensive and rigorous physical simulations of light/particles interactions, are particularly relevant and, accordingly under specific developments since several years. Therefore, the DMRC/LGCI (CEA Marcoule), in collaboration with the laboratory IUSTI (CNRS and Aix-Marseille University), develops two optical interferometric techniques suitable for R&D studies: the Digital In-line Holography (DIH) and the Rainbow Refractometry (RR). Previous works have shown that DIH allows a simultaneous measurement of 3D-positions, shape and size of flowing particles, even considering astigmatic geometries, while RR gives access to the size and refractive index of each particle or of set of particles, which considering linear optics is directly linked to their composition. This study aims to go further in multiphase flows characterization with these two technics by following three main objectives: 1) propose original solutions for the characterization of materiel compositions thanks to DIH, 2) deepen inverse methods in RR to allow the study of clouds of particles with variable compositions and to take into account gradients of concentration around a sessile drop, 3) evaluate the relevance of these technics for lab on chip systems.
Optical sensor development for in-situ and operando Li-ion battery monitoring
To improve the battery management system, it is required to have a better knowledge of the physical and chemical phenomena inside the cells. The next generation of cells will integrate sensors for deepest monitoring of the cell to improve the performances, safety, reliability and lifetime of the battery packs. The main challenge is thus to measure relevant physico-chemical parameters in the heart of the cell to get a direct access to the real state of the cell and thus to optimize its management. To address this challenge, a research project will start at CEA at the beginning of 2020 to develop innovative optical sensors for Li-ion battery monitoring. He / She will participate, in a first step, to the development of optical probes and their integration on optical fibres. The work will focus on the synthesis of a photo-chemical probe (nanoparticle and/or molecule) as active part of the sensor. Then, theses probes will be put on the optical fibre surface to form the sensor. The candidate will also participate to the realization of an optical bench dedicated to the testing of the sensors. In a second step, he / she will work on integrating the sensors into the Li-ion cells and test them in different conditions. The objective is to demonstrate the proof of concept: validation of the sensors efficiency to capture the behaviour of the cell and correlate it to electrochemical measurements.
IMPROVING OPTICALLY PUMPED MAGNETOMETERS FOR BIOMEDICAL IMAGING
Our lab works on optically pumped magnetometers (OPM) based on helium-4 metastable atoms. Our main achievement in last years has been the design and space qualification of the most advanced OPMs available for spatial exploration, which were launched on ESA Swarm mission [1]. With this very same species we have developed OPMs for medical imaging of brain (MEG) and heart (MCG), which have the advantage of operating at room temperature. The development of these two imaging techniques is an opportunity to better understand and diagnose pathologies like epilepsy, Alzheimer or arrhythmia.
A few years ago we performed proof of concept measurements of both MCG and MEG with primitive versions of our sensors [2,3]. After getting a better understanding of our sensors physics [4] and implementing substantial improvements, we are now developing arrays of OPMs and collaborating with several clinical teams in order to test them for different applications and environments. The purpose of this post-doctoral position is to contribute to the development of magnetometer arrays. It involves experimental work to improve the current prototypes of medical OPM arrays: the post-doc will be notably in charge of improving the intrinsic noise of the sensor and identifying the best way to build robust, reproducible architectures that could be replicated in arrays of several hundreds of sensors.
This work is aimed at bringing this technology to the medical imaging market, in collaboration with a start-up currently prepared by CEA-Leti. It will be carried out in a multidisciplinary team, composed of researchers, experienced engineers, PhD students and post-docs, specialized in the fields of optics, lasers, magnetism and electronics. It will also rely on collaborations with medical research teams in neurology and cardiology.
[1] http://smsc.cnes.fr/SWARM
[2] S. Morales et al.,
[3] E. Labyt et al., IEEE Transactions on Medical Imaging (2019).
[4] F. Beato et al. Physical Review A (2018)
LAB AND FIELD WORK ON OPTICALLY PUMPED MAGNETOMETERS
Our lab works on optically pumped magnetometers (OPM) based on helium-4 metastable atoms. Our main achievement in last years has been the design and space qualification of the most advanced OPMs available for spatial exploration, launched on ESA Swarm mission [1].
With this same species we have developed OPMs for medical imaging of brain (MEG) and heart (MCG), which have the advantage of operating at room temperature, with no heating or cooling.
The development of these two imaging techniques is an opportunity to better understand and diagnose pathologies like epilepsy, Alzheimer or arrhythmia.
A few years ago we performed proof of concept measurements of both MCG and MEG with primitive versions of our sensors [2,3]. After getting a better understanding of our sensors physics [4] and implementing substantial improvements, we are now developing arrays of OPMs and collaborating with several clinical teams in order to test them for different applications and environments.
The purpose of this post-doctoral position is to contribute to the development of magnetometer arrays. It involves mainly the deployment of OPM arrays in the clinical environments where they are going to be tested by several of our partner medical research teams in both neurology and cardiology. The post-doc should be able to deploy and operate the sensors in these environments, solve the practical issues, and bring feedback on all kind of improvements that are needed. He or she will also participate in the implementation of some of these improvements, and their tests in lab environment.
This work is aimed at bringing this technology to the medical imaging market. It will be carried out in a multidisciplinary team, composed of researchers and experienced engineers.
[1] http://smsc.cnes.fr/SWARM
[2] S. Morales et al., Phys. Med. B
[3] E. Labyt et al., IEEE Transactions on Medical Imaging (2019).
[4] F. Beato et al. Physical Review A (2018)
Development of a bimodal Brillouin-Raman microscope for biological tissue characterization
The Laboratory of Physics of Cytoskeleton and Morphogenesis (LPCV) at CEA Grenoble has an opening for setting up and characterizing a novel bioimaging modality combining Brillouin and Raman Spectroscopy. This is an interdisciplinary project between LPCV and the Laboratory of Imaging and Acquisition Systems (LISA) of CEA Grenoble. Brillouin microscopy allows non-invasive measurements of the visco-elastic properties of cells and tissue on the micrometer scale, while Raman microscopy gives complementary biochemical information. Such measurements have applications in the study of cytoskeleton organization, and for novel diagnostic tools based on following early mechanical and biochemical tissue alterations.
The postdoctoral scholar will be responsible for developing and coupling a Brillouin spectrometer to the Raman micro-spectrometer of LISA. This includes optical system development, instrument control and numerical data processing. He/She will characterize the instrument on model systems prepared at LPCV, and move forward to first in-cellulo experiments. The successful candidate is expected to coordinate the interaction between LPCV and LISA.
Development of femtosecond Fiber Bragg Grating acoustic receivers for the Structural Health Monitoring using passive acoustic tomography
The proposed post-doctoral fellowship is part of a transverse project initiated by the CEA and which consists in developing a prototype of a continuous monitoring system of a metallic structure (pipe for example) using fiber Bragg gratings acoustic receivers and passive imaging (or passive tomography). It aims to demonstrate the relevance of the SHM (Structural Health Monitoring) concept for nuclear facilities using optical fiber sensors operating in continuous and in extreme environment. This project is based on two recent developments: new generation of fiber Bragg gratings developed for severe environments and defect imaging algorithms based on ambient noise analysis. A demonstration of elastic wave reconstruction from passive algorithm applied to fiber Bragg gratings was carried out at the CEA in 2015, which is a world first, patented. The project aims more particularly to produce a demonstrator and to equip a pipeline on a test loop. It will provide input data relating to the ability of a moving fluid to generate elastic waves that can be analyzed in passive tomography.
Micro-energy sources for biomedical applications
There is a growing interest towards wireless implantable systems for in vivo biomedical applications. However, such implantable systems have a limited lifetime determined by the battery capacity. CEA LITEN is working on innovative miniaturized systems integrating an energy harvesting component with a rechargeable battery. This type of micro-systems will be used for powering sensors or other implantable medical devices. The post-doctoral researcher will work on the design, the fabrication and the characterization of demonstrators consisting of the energy harvesting component, the battery and a power management circuit. Numerical simulations could also be performed, with the help of specialized engineers. The characterization of the demonstrators and the numerical simulation results will allow the post-doctoral researcher to propose innovative solutions for optimizing the system. The post-doctoral researcher will work in a multi-disciplinary team, which requires strong abilities for team working and communication.
Design of a high-energy phase contrast radiography chain
As part of hydrodynamic experiments carried out at CEA-DAM, the laboratory is seeking, using pulsed X-ray imaging, to radiograph thick objects (several tens of mm), made of low-density materials (around 1 g/cm3), inside which shock waves propagate at very high speeds (several thousand m/s). For this type of application, it is necessary to use energetic X-ray sources (beyond 100 keV). Conventional X-ray imaging, which provides contrast due to variations in absorption cross sections, proves insufficient to capture the small density variations expected during the passage of the shock wave. A theoretical study recently carried out in the laboratory showed that the complementary exploitation of the information contained in the X-ray phase should enable better detectability. The aim of the post-doctorate is to provide experimental proof of concept for this theoretical study. For greater ease of implementation, the work will mainly focus on the dimensioning of a static X-ray chain, where the target is stationary and the source emits continuous X-ray radiation. Firstly, the candidate will have to characterize in detail the spectrum of the selected X-ray source as well as the response of the associated detector. In a second step, he (she) will design and have manufactured interference gratings adapted to high-energy phase measurements, as well as a representative model of the future moving objects to be characterized. Finally, the student will carry out radiographic measurements and compare them with predictive simulations. The student should have a good knowledge of radiation-matter interaction and/or physical and geometric optics. Proficiency in object-oriented programming and/or the Python and C++ languages would be a plus.