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By leveraging metamaterials and compressive imaging, a low-profile aperture capable of microwave imaging without lenses, moving parts, or phase shifters is demonstrated. This designer aperture allows image compression to be performed on the physical hardware layer rather than in the postprocessing stage, thus averting the detector, storage, and transmission costs associated with full diffraction-limited sampling of a scene. A guided-wave metamaterial aperture is used to perform compressive image reconstruction at 10 frames per second of two-dimensional (range and angle) sparse still and video scenes at K-band (18 to 26 gigahertz) frequencies, using frequency diversity to avoid mechanical scanning. Image acquisition is accomplished with a 40:1 compression ratio.

An imaging technique has been developed to characterize state mixtures caused by partial coherence and fluctuations in dynamical systems. Diffractive imaging collects mixed messages Some of the most impressive advances in imaging depend on there being high coherence in the probe beam and the sample being imaged. But most systems exhibit a mixture of states — arising from fluctuations in the probe beam, the sample and/or the detector itself — that usually represent an unwanted complication for imaging. Pierre Thibault and Andreas Menzel have developed a general methodology for characterizing these mixed states as a means of improving image reconstructions in the presence of partial coherence. The method, which exploits a hitherto unrecognized connection between coherent diffraction measurements and quantum state tomography, has the potential to open up new imaging applications in both classical and quantum systems. Progress in imaging and metrology depends on exquisite control over and comprehensive characterization of wave fields. As reflected in its name, coherent diffractive imaging relies on high coherence when reconstructing highly resolved images from diffraction intensities alone without the need for image-forming lenses 1 , 2 , 3 . Fully coherent light can be described adequately by a single pure state. Yet partial coherence and imperfect detection often need to be accounted for, requiring statistical optics or the superposition of states 4 , 5 . Furthermore, the dynamics of samples are increasingly the very objectives of experiments 6 . Here we provide a general analytic approach to the characterization of diffractive imaging systems that can be described as low-rank mixed states. We use experimental data and simulations to show how the reconstruction technique compensates for and characterizes various sources of decoherence quantitatively. Based on ptychography 7 , 8 , the procedure is closely related to quantum state tomography and is equally applicable to high-resolution microscopy, wave sensing and fluctuation measurements. As a result, some of the most stringent experimental conditions in ptychography can be relaxed, and susceptibility to imaging artefacts is reduced. Furthermore, the method yields high-resolution images of mixed states within the sample, which may include quantum mixtures or fast stationary stochastic processes such as vibrations, switching or steady flows.

We introduce a new type of liquid cell for in situ transmission electron microscopy (TEM) based on entrapment of a liquid film between layers of graphene. The graphene liquid cell facilitates atomic-level resolution imaging while sustaining the most realistic liquid conditions achievable under electron-beam radiation. We employ this cell to explore the mechanism of colloidal platinum nanocrystal growth. Direct atomic-resolution imaging allows us to visualize critical steps in the process, including site-selective coalescence, structural reshaping after coalescence, and surface faceting.

A new multiplex technique of coherent anti-Stokes Raman spectro-imaging with two laser frequency combs is shown to record molecular spectra of broad bandwidth on a microsecond scale. Raman spectroscopy with laser frequency combs Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. Particularly valuable are label-free methods capable of probing complex systems in a non-destructive and chemically sensitive manner, ideally with high spatial and temporal resolution. This is offered by coherent Raman spectroscopy, and here Takuro Ideguchi et al now show that it can be implemented using two laser frequency combs and thereby allow spectra covering a wide bandwidth to be measured with high resolution on a single detector on the microsecond timescale. With further system development, the method is expected to offer exciting new possibilities not only in spectroscopy but also for real-time microscopy observations of, for example, biological processes. Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool 1 , 2 for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates 3 , 4 by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection 5 or frequency-swept laser beams 6 , 7 , 8 , 9 . Laser frequency combs 10 are finding increasing use for broadband molecular linear absorption spectroscopy 11 , 12 , 13 , 14 , 15 . Here we show, by exploring their potential for nonlinear spectroscopy 16 , that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

The neuroanatomical architecture is considered to be the basis for understanding brain function and dysfunction. However, existing imaging tools have limitations for brainwide mapping of neural circuits at a mesoscale level. We developed a micro-optical sectioning tomography (MOST) system that can provide micrometer-scale tomography of a centimeter-sized whole mouse brain. Using MOST, we obtained a three-dimensional structural data set of a Golgi-stained whole mouse brain at the neurite level. The morphology and spatial locations of neurons and traces of neurites could be clearly distinguished. We found that neighboring Purkinje cells stick to each other.

Recent advances in far-field fluorescence microscopy have led to substantial improvements in image resolution, achieving a near-molecular resolution of 20 to 30 nanometers in the two lateral dimensions. Three-dimensional (3D) nanoscale-resolution imaging, however, remains a challenge. We demonstrated 3D stochastic optical reconstruction microscopy (STORM) by using optical astigmatism to determine both axial and lateral positions of individual fluorophores with nanometer accuracy. Iterative, stochastic activation of photoswitchable probes enables high-precision 3D localization of each probe, and thus the construction of a 3D image, without scanning the sample. Using this approach, we achieved an image resolution of 20 to 30 nanometers in the lateral dimensions and 50 to 60 nanometers in the axial dimension. This development allowed us to resolve the 3D morphology of nanoscopic cellular structures.

A single electron in a defined orbital is found to interact with a quantum many-body system through electron–phonon coupling. A single electron coupled to a quantum gas The coupling of electrons to matter underlies important material properties such as electrical conductivity and superconductivity. Jonathan Balewski and colleagues have created a novel experimental system that allows this coupling to be studied in a very pure form: a single localized electron interacting with a Bose–Einstein condensate — an ultracold quantum gas. The electron is provided by one of the rubidium atoms in the condensate, excited to a very high energy level, but still bound to the charged nucleus. In this 'Rydberg state', the electron's orbit spans up to eight micrometres — comparable to the dimensions of the condensate, allowing the electron to interact with several tens of thousands of atoms. The authors anticipate future experiments on electron orbital imaging, investigation of phonon-mediated coupling of single electrons, and applications in quantum optics. The coupling of electrons to matter lies at the heart of our understanding of material properties such as electrical conductivity. Electron–phonon coupling can lead to the formation of a Cooper pair out of two repelling electrons, which forms the basis for Bardeen–Cooper–Schrieffer superconductivity 1 . Here we study the interaction of a single localized electron with a Bose–Einstein condensate and show that the electron can excite phonons and eventually trigger a collective oscillation of the whole condensate. We find that the coupling is surprisingly strong compared to that of ionic impurities, owing to the more favourable mass ratio. The electron is held in place by a single charged ionic core, forming a Rydberg bound state. This Rydberg electron is described by a wavefunction extending to a size of up to eight micrometres, comparable to the dimensions of the condensate. In such a state, corresponding to a principal quantum number of n = 202, the Rydberg electron is interacting with several tens of thousands of condensed atoms contained within its orbit. We observe surprisingly long lifetimes and finite size effects caused by the electron exploring the outer regions of the condensate. We anticipate future experiments on electron orbital imaging, the investigation of phonon-mediated coupling of single electrons, and applications in quantum optics.

Crystal mapping Synchrotron X-ray radiation, produced by electron accelerators at central facilities, can now be produced in extremely narrow coherent beams. When these X-rays illuminate a crystal of nanometre dimensions a diffraction pattern emerges that is highly resolved. This provides a powerful new tool for structural analysis, as the fine features of the diffraction pattern can be interpreted in terms of sub-atomic distortions within the crystal attributable to its contact with an external support. Coherent X-ray diffraction patterns derived from third-generation synchrotron radiation sources can lead to quantitative three-dimensional imaging of lattice strain on the nanometre scale. Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals 1 , 2 , 3 . Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate 4 . When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a ‘complex’ crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative three-dimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials 4 . Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers 5 , 6 , 7 .

The image of a fluorescent object hidden behind an opaque layer can be retrieved non-invasively by exploiting the correlation properties of the speckle pattern produced by illuminating the object through the layer using laser light. Seeing through the fog with non-invasive imaging Imaging through opaque, light-scattering layers is an important capability in many fields, including nanotechnology and the biosciences. Several promising methods are being developed, but typically involve invasive procedures such a placing a detector or nonlinear material behind the scattering layer. Jacopo Bertolotti et al . now demonstrate a non-invasive imaging procedure that makes use of the correlations in the speckled intensity pattern that is produced when laser light passes through a scattering medium. Fluorescent micrometre-sized objects obscured by scattering layers can be imaged by measuring total fluorescence at several different angles of laser incidence and by using an iterative algorithm that disentangles the spatial information of the object and the speckle pattern. The authors successfully construct detailed images of cell-sized fluorescent objects hidden six millimetres behind scattering layers, and a complex biological sample sandwiched between two opaque screens. Non-invasive optical imaging techniques, such as optical coherence tomography 1 , 2 , 3 , are essential diagnostic tools in many disciplines, from the life sciences to nanotechnology. However, present methods are not able to image through opaque layers that scatter all the incident light 4 , 5 . Even a very thin layer of a scattering material can appear opaque and hide any objects behind it 6 . Although great progress has been made recently with methods such as ghost imaging 7 , 8 and wavefront shaping 9 , 10 , 11 , present procedures are still invasive because they require either a detector 12 or a nonlinear material 13 to be placed behind the scattering layer. Here we report an optical method that allows non-invasive imaging of a fluorescent object that is completely hidden behind an opaque scattering layer. We illuminate the object with laser light that has passed through the scattering layer. We scan the angle of incidence of the laser beam and detect the total fluorescence of the object from the front. From the detected signal, we obtain the image of the hidden object using an iterative algorithm 14 , 15 . As a proof of concept, we retrieve a detailed image of a fluorescent object, comparable in size (50 micrometres) to a typical human cell, hidden 6 millimetres behind an opaque optical diffuser, and an image of a complex biological sample enclosed between two opaque screens. This approach to non-invasive imaging through strongly scattering media can be generalized to other contrast mechanisms and geometries.

Single-electron wavefunctions, or orbitals, are the mathematical constructs used to describe the multi-electron wavefunction of molecules. Because the highest-lying orbitals are responsible for chemical properties, they are of particular interest. To observe these orbitals change as bonds are formed and broken is to observe the essence of chemistry. Yet single orbitals are difficult to observe experimentally, and until now, this has been impossible on the timescale of chemical reactions. Here we demonstrate that the full three-dimensional structure of a single orbital can be imaged by a seemingly unlikely technique, using high harmonics generated from intense femtosecond laser pulses focused on aligned molecules. Applying this approach to a series of molecular alignments, we accomplish a tomographic reconstruction of the highest occupied molecular orbital of N2. The method also allows us to follow the attosecond dynamics of an electron wave packet.