Modulation d'amplitude en quadrature

La modulation d'amplitude en quadrature (en anglais, quadrature amplitude modulation : QAM) est une forme de modulation d'une porteuse par modification de l'amplitude de la porteuse elle-même et d'une onde en quadrature (une onde déphasée de 90° avec la porteuse) selon l'information transportée par deux signaux d'entrée. Autrement dit, cela peut être considéré (utilisant une notation en nombre complexe) comme une simple modulation d'amplitude d'une onde, exprimée en complexe, par un signal, exprimé en complexe. Cela signifie que l'amplitude et la phase de la porteuse sont simultanément modifiées en fonction de l'information à transmettre. La modulation de phase peut également être considérée comme un cas particulier de la modulation d'amplitude en quadrature, où seule la phase varie. Cette remarque peut également être étendue à la modulation de fréquence car cette dernière peut être vue comme un cas particulier de la modulation de phase. Utilisations QAM est utilisée d

Amplitude and phase reconstruction for Low-Energy Electron Holography of individual proteins

Hannah Julia Ochner

Single-molecule imaging methods are of importance in structural biology, and specifically in the imaging of proteins, since they can elucidate conformational variability and structural changes that might be lost in imaging methods relying on averaging processes. Low-energy electron holography (LEEH) is a promising technique for imaging individual proteins with negligible radiation damage, which can be combined with a sample preparation process by native electrospray ion beam deposition (native ES-IBD) ensuring the creation of chemically pure samples suitable for holographic imaging.The central step in the analysis of data measured by LEEH is the numerical reconstruction of the object from the experimentally acquired holograms.Full information about the imaged object consists of both amplitude and phase information imprinted on the scattered wave during the interaction of the electron beam with the molecule and encoded in the hologram created by the interference of the scattered wave and the transmitted incident wave. A propagation-based algorithm with the goal of reconstructing the wave field in the plane of the object is presented and applied to holograms of individual proteins prepared by ES-IBD and measured with a low-energy electron holography microscope. The information retrieved from the reconstruction of the amplitude distribution in the object plane is discussed by analysing holograms of antibodies, demonstrating that the inherent conformational variability of these molecules can be mapped by LEEH. The influence of the sample preparation process on the surface conformations is tracked by tuning the landing energy of the proteins during deposition.To complement the amplitude data, an iterative phase retrieval algorithm is implemented to reconstruct the phase distribution in the object plane along with the amplitude distribution. The algorithm's performance and robustness is thoroughly evaluated and simulations regarding multiple scattering effects and element-dependent variations in scattering strength are carried out to provide a reference for the interpretation of phase data retrieved from experimentally acquired holograms. The iterative phase retrieval algorithm is then applied to protein data, indicating that both molecular density and charges can be related to features in the phase reconstructions, while the presence of metals does not correlate with specific phase signals at the current resolution obtainable from the experimental data.Since proteins are inherently three-dimensional, approaches towards three-dimensional reconstruction schemes are discussed, which will be the focus of future work.

EPFL2022

Advanced Techniques in Optical Diffraction Tomography

Ahmed Bassam Sayed Ayoub Mohamed Emam

In this thesis, we study the 3 challenges described above. First, we study different reconstruction techniques and assess the fidelity of each reconstruction results by means of structured illumination and phase conjugation. By reconstructing the 3D refractive index of the sample using different algorithms (i.e. Born, Rytov, and Radon) and then perform a numerical back-propagation of experimentally measured structured illumination pattern we are able to assess the fidelity of each reconstruction algorithms without prior information about the 3D RI distribution of the sample.The second part of the thesis is concerned with the 3D reconstruction of samples using intensity-only measurements which the need to holographically acquire them. We show that using intensity-only measurements, we could still be able to reconstruct the 3D volume of the sample with edge-enhanced effects which was proven useful for drug delivery applications in which nano-particles were identified on the cell membrane of immune T-cells in a drug delivery studies. Such reconstruction technique would result in more robust imaging system where the commercial imaging microscope systems can be incorporated with LEDs for high-quality speckle noise-free imaging systems. In addition, we show that under certain conditions, we can be able to reconstruct the 3D refractive index distribution of different samples.The third part of the thesis is contributing to high-speed complex wave-front shaping using DMDs. In that part, new modulation technique is demonstrated that can boost the speed of the current time-multiplexing techniques by a factor of 32. The modulation technique is based on amplitude modulation where an amplitude modulator is synchronized withvthe DMD to modulate the intensity of each bit-plane of an 8-bit image and then all the modulated bit-planes are linearly added on the detector. Such modulation technique can be used not only for structured illumination microscopy but also for high-speed 3D printing applications as well as projectors.The last part is concerned with using deep learning approaches to solve the missing cone problem usually accompanied with optical imaging due to the limited numerical aperture of the imaging system. Two techniques are discussed; the first is based on using a physical model to enhance the quality of the 3D RI reconstruction and the second is based on using deep neural network to solve the missing cone problem.

EPFL2022

Magnonic crystals with reconfigurable magnetic defects for spin-based microwave electronics

Korbinian Baumgärtl

Collective spin excitations can propagate in magnetically ordered materials in the form of waves. These so-called spin waves (SWs) or magnons are promising for low-power beyond-CMOS information processing, which does not rely anymore on the lossy movement of electric charges. SWs in the few GHz frequency regime possess nanoscale wavelengths about five orders of magnitude smaller than electromagnetic waves of the same frequency. This property makes SWs ideally suited for application in microwave technology, essential for on-chip processing of wireless telecommunication signals. In this thesis, three crucial challenges relevant for the technological application of SWs are addressed: First, to functionalize SWs and exploit their small wavelengths, it is necessary to control them at the nanoscale. Here, periodically nanostructured materials, denoted magnonic crystals, are promising, as they allow to tailor the band structure of SWs. We report on SWs propagating in a prototypical one-dimensional magnonic crystal consisting of dipolarly coupled magnetic nanostripes. The remanent magnetization of individual stripes was designed to be bistable along the long axis. By magnetizing an individual stripe in opposite direction to the others, we created a magnetic defect. We measured by means of all-electrical spin wave spectroscopy and Brillouin light scattering microscopy phase and amplitude of SWs trespassing the defect. We found that SW phases and amplitudes were modified at the nanoscale, and phase shifts could be tuned by an applied bias magnetic field. Using micromagnetic simulations, we identified specific bias fields for which phase shifts of Pi are achieved without suppressing SW amplitudes. This result is highly relevant for the implementation of logic gates based on interference of phase-controlled SWs. We further measured propagation of short-waved SWs in an antiferromagnetically ordered one-dimensional magnonic crystal, where every second stripe was magnetized in opposite direction. We found a band gap closing at the Brillouin zone boundary when no magnetic bias field was applied. Our observations are promising for reprogrammable microwave filters capable of adjusting stop- and passband. Second, we address how long-waved electromagnetic waves can be coupled efficiently to nanoscale SWs. We demonstrate by space- and time-resolved scanning X-ray transmission measurements, that excited nanogratings allow to transfer their reciprocal lattice vector and multiple of it to an underlying magnetic thin film, in which nanoscale propagating SWs are launched. Additionally, we discovered a second method for short-waved SW generation based on magnetic microwave guides. This approach is easy to fabricate and relies on the adaption of the SW wavelength to a changing effective magnetic field. Efficient coupling of electromagnetic waves to nanoscale SWs promises an unprecedented miniaturization of microwave components. Third, we found that the magnetization direction of bistable nanomagnets can be switched by propagating SWs in an underlying magnetic thin film when a threshold amplitude is reached. This discovery is promising for the realization of a non-volatile magnonic memory, which stores SW amplitudes. A possible application are SW logic gates, which encode the outcome of a logic operation in the output SW amplitude. Magnonic memory would allow for storing these amplitudes directly, without requiring lossy conversion into the electrical domain.

EPFL2021

Magnonic crystals with reconfigurable magnetic defects for spin-based microwave electronics

Korbinian Baumgärtl

EPFL2021

Amplitude and phase reconstruction for Low-Energy Electron Holography of individual proteins

Hannah Julia Ochner

EPFL2022

Advanced Techniques in Optical Diffraction Tomography

Ahmed Bassam Sayed Ayoub Mohamed Emam

EPFL2022