The recently developed magnetic encoding beam microscopy approach to imaging with neutral atomic beams has a spatial resolution that is limited by the spread of velocities within the beam. Here we present a solution for overcoming this restriction which is based on adding a homogeneous magnetic field and resolving both the spatial resolution and the de Broglie wavelength of the particles using sequential Fourier transforms. Numerical simulations are used to demonstrate the enhanced resolution obtained with this approach, and how features which were lost in the spatial reconstruction due to the spread of velocities can be recovered. Wavelength/velocity resolved profiles that were reconstructed from experimental data are presented, demonstrating how the scheme can be applied in practice.
The recently developed magnetic encoding beam microscopy approach to imaging with neutral atomic beams has a spatial resolution that is limited by the spread of velocities within the beam. Here we present a solution for overcoming this restriction which is based on adding a homogeneous magnetic field and resolving both the spatial resolution and the de Broglie wavelength of the particles using sequential Fourier transforms. Numerical simulations are used to demonstrate the enhanced resolution obtained with this approach, and how features which were lost in the spatial reconstruction due to the spread of velocities can be recovered. Wavelength/velocity resolved profiles that were reconstructed from experimental data are presented, demonstrating how the scheme can be applied in practice.
The emerging technique of neutral beam microscopy offers a non-perturbative way of imaging surfaces of various materials which cannot be studied using conventional microscopes. Current neutral beam microscopes use either diffractive focusing or pin-hole scanning to achieve spatial resolution, and are characterised by a strong dependence of the imaging time on the required resolution. In this work we introduce an alternative method for achieving spatial resolution with neutral atom beams which is based on manipulating the magnetic moments of the beam particles in a gradient field, and is characterised by a much weaker dependence of the imaging time on the image resolution. The validity of the imaging approach is demonstrated experimentally by reconstructing one dimensional profiles of the beam which are in good agreement with numerical simulation calculations. Numerical simulations are used to demonstrate the dependence of the signal to noise on the scan resolution and the topography of the sample, and assess the broadening effect due to the spread of velocities of the beam particles. The route towards implementing magnetic encoding in high resolution microscopes is discussed.
The resolution of imaging devices is ultimately limited by the diffraction of light. This limit can be circumvented by exploiting near-field phenomena, non-linearities of the sample or specific illumination schemes, which led to the recent explosion of optical super-resolution techniques. However, it would be desirable to reach the nanoscale in the most general way possible, with far-field linear imaging of uniformly illuminated samples. In the last few years, the answer to that came with the field of quantum-inspired super-resolution (QISR), where quantum metrological techniques were used to find novel measurement schemes that, beyond the conventional direct imaging of light, would achieve higher precisions. Interestingly, these ideas would always in some way or another involve transverse spatial modes of light. This thesis presents our work on the subject, with novel theoretical and experimental results. Firstly, we develop the traditional theory of QISR, with has mostly focused on either the estimation of separation of two point sources or on geometric moments of samples. Then, we introduce our own results on optical imaging of general distributions of point sources, in a step to take QISR from toy examples to real imaging scenarios. Secondly, we apply all the concepts studied on a experimental, proof-of-principle implementation of a QISR scheme dubbed Hermite-Gaussian Microscopy (HGM), which uses heterodyne detection with several Hermite-Gaussian modes as local oscillator in order to reconstruct the object sample and achieve super-resolution. We report the techniques necessary for the manipulation of spatial modes of light, as well as our results, where we demonstrated 2D imaging with twofold resolution enhancement beyond the diffraction limit.
Electron diffraction from nanogratings provides a platform for free-electron interferometry, yet controlled manipulation of electron spin in such geometries remains largely unexplored. In particular, the role of the self-generated magnetic field arising from electron motion and the feasibility of coherent spin control without disrupting diffraction coherence have not been quantitatively investigated. In this article, a self-consistent Maxwell-Pauli framework is developed to study spin-resolved electron diffraction from nanogratings in the presence of magnetic fields. The model incorporates geometric confinement, image-charge interactions, self-generated magnetostatic fields, and externally applied magnetic fields. Numerical simulations show that the intrinsic magnetic self-field produced by the electron probability current is several orders of magnitude too weak to induce measurable spin mixing, demonstrating that nanogratings act as spin-conserving beam splitters under field-free conditions. When a uniform magnetic field is applied upstream of the nanograting, coherent Larmor precession enables controlled spin rotation without modifying the diffraction geometry or degrading coherence. The magnetic field required for a π spin rotation scales inversely with the interaction length and electron de Broglie wavelength λdB. Furthermore, a downstream nonuniform magnetic field applied after the nanograting imparts a spatially varying Zeeman phase, producing opposite transverse momentum shifts for the two spin components. The spin-dependent transverse dynamics is analyzed using Husimi Q-function phase-space maps, which visualize spin-dependent population redistribution and momentum separation. The proposed approach enables tunable spatial separation of spin-resolved free electron beams and establishes an all-magnetic route for coherent spin rotation, control, and interferometry.
Super-resolution microscopy is crucial for imaging sub-wavelength biological structures. However, most techniques rely on nonlinear saturation or stochastic switching of emitters, limiting imaging speed and increasing phototoxicity. Here, we achieve deep super-resolution without employing saturation or stochastic dynamics, instead using a form of spatial mode demultiplexing. By shaping the point-spread function of the emitted light, our Structured Detection Microscope (SDM) redistributes information away from high shot-noise regions of the image, enhancing sensitivity to sub-diffraction emitter separations in two-dimensions and without mode-sorting optics. Implementing SDM within a high-numerical aperture total internal reflection fluorescence microscope, we demonstrate imaging of fluorophores attached to DNA nanorulers with separations as small as 50 nm at resolutions surpassing 40 nm - fivefold below the diffraction limit. This shows that spatial mode demultiplexing can achieve far sub-wavelength resolution and is applicable to biologically relevant samples. By enabling super-resolution biomolecular imaging without emitter saturation and stochasticity, our work opens the door to better understanding biological structure, function and dynamics.
This dissertation presents progress on an atomic beam brightening and focusing experiment that has been shown to create a beam with higher brightness and greater resolution than that of any previous atomic focusing experiment. Our method of beam brightening relies upon using a permanent magnetic hexapole as a lens in conjunction with transverse laser cooling to focus and collimate a supersonic beam of metastable neon atoms. We then use an adjustable electromagnetic hexapole as a lens to focus the brightened atomic beam. Neutral atom beams have long been used as a tool to spectroscopically probe two dimensional surfaces, however the lack of a means to create bright, high-resolution neutral atom beams has limited their utility as a nanoscale resolution probing mechanism. While optical and electron microscopy have been the workhorses of microscopy for decades, we believe that our scheme for beam brightening and focusing will unleash the promise of neutral atom microscopy. Our scheme of beam brightening and focusing can be repeated in series and reveals a pathway to true high density nanoscale neutral atom focusing. Simulations suggest that when combined with aberration correction, our scheme will be able to produce an atomic beam with sufficient brightness and resolution to be useful as a surface sensitive nanoscale probe.
Experimental results on phase-space imaging of a laser- cooled atomic cloud are presented. Both position and velocity information are encoded in the frequency of the signal coherently radiated from the cloud. This encoding is achieved by application of a position-dependent magnetic field. Fourier transformation of the signal yields a projection of the phase-space density of the atoms. Imprinting a structure on the cloud we observe its time `sheering' evolution in the phase-space. Since the projection direction is determined by the imposed field gradient, we can reconstruct the phase-space structure of the cloud.