The central objective of this internship is to establish a reproducible route for fabricating europium molecular membranes and, crucially, to determine whether their exceptional optical properties are preserved after exfoliation and transfer. The student will optimize the mechanical exfoliation conditions to increase the yield of thin, large-area flakes; develop deterministic dry-transfer protocols onto photonic substrates such as SiC, SiO2/Si and glass; characterize membrane thickness, morphology and crystalline quality using optical interference microscopy, atomic force microscopy and Raman spectroscopy; and investigate their luminescence and optical homogeneous linewidths at cryogenic temperatures using spectral hole burning. Comparison with bulk crystals will allow the influence of exfoliation, reduced thickness and substrate coupling on the optical coherence of the molecular material to be established.

This project aims to uncover the biophysical principles that enable mammalian embryonic stem cells to self-organize into three-dimensional structures resembling developing embryos. How do cells acquire their identities and positional information, and how does precise and reproducible spatial organization emerge from their collective behavior? Combining quantitative microscopy, image analysis, mathematical modeling, and machine learning, the project will investigate the emergence of positional and correlative information during stem-cell differentiation and the flow of information through genetic networks. By linking theory and experiments, we aim to identify general principles of developmental self-organization and compare information processing across different biological systems, including mammalian stem-cell aggregates and Drosophila embryos.

This internship will focus on measuring mid-infrared molecular transitions of methanol (CH3OH), ammonia (NH3), and other molecules known for their enhanced sensitivity to changes in µ. The work will involve achieving subDoppler spectroscopic resolution to reach target laboratory frequency accuracies of ~100 Hz needed for comparisons with astronomical observations. This activity is part of the ANR Ultiµos project, a collaborative effort which seeks to refine current constraints on the possible variation of µ which involves leading research institutions, including Laboratoire Kastler Brossel (LKB, L. Hilico) and MONARIS (C. Janssen) at Sorbonne Université. The three partners of the Ultiµos consortium will collaborate to conduct measurements in different spectral windows, to identify transitions as targets for future Earth/space comparison campaigns, which could further tighten constraints on variations of µ. Other collaborators, such as Vrije Universiteit Amsterdam and Onsala Space Observatory, will provide theoretical and observational/astronomical support to complement the experimental efforts.

Photosynthetic micro-organisms contribute for half of dioxygen production, consume carbon dioxide, and are promising regarding biofuel production. Our lab aims to develop a quantitative approach describing the energetic state of these micro-organisms exploring their environment, a crucial aspect to better understand their motility behaviour. To tackle this problem, we use the motile micro-algae Chlamydomonas reinhardtii, a model unicellular organism, per-forming photosynthesis (light-to-chemical energy conversion) and phototaxis (cell reorientation along the light direction). Two projects are available.

When two miscible liquids meet, transient composition gradients across their boundary generate an effective interfacial tension. This gives rise to complex interfacial flow dynamics governed by tightly coupled mass and momentum transport: a fundamental problem with broad implications in microfluidics, active mixing, and soft matter physics. In this project, the student will investigate these interfacial flows through a combination of precision experiments and physical modelling. You will design and prototype custom millifluidic channels (using3D printing and microfabrication, no prior knowledge about it required) and perform micro-PIV measurements on a state-of-the-art inverted fluorescence microscope to map local velocity fields at the interface. Depending on the candidates background, the experimental work can be complemented by analytical scaling laws and calculations or numerical simulations.

According to Anderson, the most profound and interesting problem in condensed matter physics is the glass transition. Indeed, glassy materials are ubiquitous in nature, and discussions of the glass transition involve many areas of physics. Despite intense interest in the dynamic slowing down that accompanies glass formation, a complete microscopic theory does not yet exist. Recently, the supposed existence of a length scale ξ for cooperative rearrangement has generated considerable interest in an alternative approach: the study of confined glasses. The correlation length scales emerging in these systems appear to be much larger than molecular sizes, which intrigues the community. We propose to address the problem of confined glass transition on a silica nanoparticle isolated from its environment using optical trapping in vacuum. The proposed method involves significantly modifying/improving an experimental system [1,2,3] whose basis has already been developed at LOMA for other fields of application. The originality of our new device is that it will enable independent determination of the size, refractive indices (real and imaginary) and temperature of a glass former nanoparticle optically trapped at a wavelength of 1064 nm [4,5]. The addition of an extra CO2 laser will enable us to finely control the temperature of the nanoparticle whose position is resolved in 3D using ultra fast interferometric detection [1,5].

Biology processes information with ions flowing through nanochannels. Artificial nanofluidic devices made from 2D materials such as graphene now show ionic memory, which recent optical observations attribute to voltage-induced deformation of the channels. The physics behind this deformation remains poorly understood. In this internship, the student will fabricate model devices, submerged 2D flakes on substrates, and measure how the electrostatic pressure competes with interlayer adhesion, using coupled optical and electrokinetic measurements. Tuning the substrate roughness will then allow control of adhesion. The goal is a quantitative model identifying the key parameters for designing ionic memories.

The goal of this internship is to develop and characterize nonlinear acousto-optic devices operating in the mid-infrared (wavelength of 3-8µm), leveraging broadband transparency and piezoelectricity of III-V semiconductor heterostructures. These devices will perform phase modulation, but also potentially on-chip optical routing, a pre-requisite for magnetic field-free optical isolation. The internship will be mostly experimental, involving the use and development of two existing setups. The first one is a mid-IR integrated photonic bench allowing to characterize the operation of the devices (see above, right). The second one is a heterodyne interferometer, that allows to image the SAW-related vibration (amplitude and phase) of the sample surface to characterize the acoustic properties of the devices (see above, left).

Various mechanisms underlie metal-insulator transitions in condensed matter. One of these mechanisms is Anderson localization, which is caused by quantum interference induced by disorder. As a consequence, the Drude diffusion of an electron through the sample has to be corrected, and when the interferences become large enough, conduction may cease, leading to an insulating phase. Because the origin of this phenomenon lies in interference, it has been suggested 40 years ago by Anderson himself that it should be easily observed using "classical" waves as light or sound. A signature of localization lies in the transmission transverse profile: in the diffusion regime, a Gaussian beam spreads in time whereas in the localization regime it saturates. This transverse profile beam spreading should be independent of transmission. The intern will perform an experimental test of the independence of the claim that the transverse profile spreading in the presence of Anderson localization does not depend on absorption.

Historically, photonic crystals and the concept of photonic bandgap were introduced in the seminal works of Yablonovitch and John in the 1980s. Even if natural examples exists (for instance in the blue iridescent wings of the Morpho butterfly), the first experimental realizations were done in the microwave regime by drilling holes in epoxy resin, and over the last 15 years, significant progresses in the micro and nano fabrication have been achieved enabling the availability of 3D materials with gaps or pseudo-gaps in the near-infrared. Nevertheless, despite a considerable amount of work reporting the measurement of photonic band gaps in different regimes (optical, infrared or microwave), an explanation of when to expect or not to expect a band gap is still lacking. Furthermore, even when a bandgap does exist, it is unclear exactly at which frequency it will occur and how wide it will be. Using bandgap computation to compute the bandgap frequency and width fluctuations in two-dimensional hyperuniform dielectric materials, we propose to explore the idea of a possible continuous phase transition in the appearance of the bandgap using finite size scaling.

Light transport is in general reciprocal, and therefore the statement "if I see you, you see me" is in general true. The magneto optical Faraday effect is one way to break reciprocity, and it is used in optical isolators for instance. In our group, we are interested in more fundamental questions raised by the presence or not of reciprocity and its consequences on multiple scattering, and we work in particular with optical fibers as the propagation medium. The Faraday effect, and thus reciprocity breaking, is proportional to the external applied magnetic field and to the length of the Faraday active medium. The proportionality constant—called the Verdet constant—is for most materials quite low, meaning that reciprocity can only be substantially broken over very large distances for the magnetic fields achievable in the lab. We would therefore like to fabricate an optical fiber with a large Verdet constant. Silica optical fibers doped with a small concentration of Gadolinium seem to be good candidates, as the Verdet constant of Gd-doped fibers was reported to be 2 orders of magnitude larger than standard telecom optical fibers, with reasonably low losses. For this work, we propose to fabricate Gd-doped optical fibers, and then characterize then both optically and magneto-optically.