ResearchPad - optics https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale]]> https://www.researchpad.co/article/elastic_article_15495 Active plasmonic and nanophotonic systems require switchable materials with extreme material contrast, short switching times, and negligible degradation. On the quest for these supreme properties, an in-depth understanding of the nanoscopic processes is essential. Here, we unravel the nanoscopic details of the phase transition dynamics of metallic magnesium (Mg) to dielectric magnesium hydride (MgH2) using free-standing films for in situ nanoimaging. A characteristic MgH2 phonon resonance is used to achieve unprecedented chemical specificity between the material states. Our results reveal that the hydride phase nucleates at grain boundaries, from where the hydrogenation progresses into the adjoining nanocrystallites. We measure a much faster nanoscopic hydride phase propagation in comparison to the macroscopic propagation dynamics. Our innovative method offers an engineering strategy to overcome the hitherto limited diffusion coefficients and has substantial impact on the further design, development, and analysis of switchable phase transition as well as hydrogen storage and generation materials.

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<![CDATA[Exosome-templated nanoplasmonics for multiparametric molecular profiling]]> https://www.researchpad.co/article/elastic_article_15463 Exosomes are nanoscale vesicles distinguished by characteristic biophysical and biomolecular features; current analytical approaches, however, remain univariate. Here, we develop a dedicated platform for multiparametric exosome analysis—through simultaneous biophysical and biomolecular evaluation of the same vesicles—directly in clinical biofluids. Termed templated plasmonics for exosomes, the technology leverages in situ growth of gold nanoshells on vesicles to achieve multiselectivity. For biophysical selectivity, the nanoshell formation is templated by and tuned to distinguish exosome dimensions. For biomolecular selectivity, the nanoshell plasmonics locally quenches fluorescent probes only if they are target-bound on the same vesicle. The technology thus achieves multiplexed analysis of diverse exosomal biomarkers (e.g., proteins and microRNAs) but remains unresponsive to nonvesicle biomarkers. When implemented on a microfluidic, smartphone-based sensor, the platform is rapid, sensitive, and wash-free. It not only distinguished biomarker organizational states in native clinical samples but also showed that the exosomal subpopulation could more accurately differentiate patient prognosis.

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<![CDATA[Quantitative and correlative extreme ultraviolet coherent imaging of mouse hippocampal neurons at high resolution]]> https://www.researchpad.co/article/elastic_article_15438 Microscopy with extreme ultraviolet (EUV) light can provide many advantages over optical, hard x-ray or electron-based techniques. However, traditional EUV sources and optics have large disadvantages of scale and cost. Here, we demonstrate the use of a laboratory-scale, coherent EUV source to image biological samples—mouse hippocampal neurons—providing quantitative phase and amplitude transmission information with a lateral resolution of 80 nm and an axial sensitivity of ~1 nm. A comparison with fluorescence imaging of the same samples demonstrated EUV imaging was able to identify, without the need for staining or superresolution techniques, <100-nm-wide and <10-nm-thick structures not observable from the fluorescence images. Unlike hard x-ray microscopy, no damage is observed of the delicate neuron structure. The combination of previously demonstrated tomographic imaging techniques with the latest advances in laser technologies and coherent EUV sources has the potential for high-resolution element-specific imaging within biological structures in 3D.

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<![CDATA[Three-dimensional vectorial holography based on machine learning inverse design]]> https://www.researchpad.co/article/elastic_article_15375 The three-dimensional (3D) vectorial nature of electromagnetic waves of light has not only played a fundamental role in science but also driven disruptive applications in optical display, microscopy, and manipulation. However, conventional optical holography can address only the amplitude and phase information of an optical beam, leaving the 3D vectorial feature of light completely inaccessible. We demonstrate 3D vectorial holography where an arbitrary 3D vectorial field distribution on a wavefront can be precisely reconstructed using the machine learning inverse design based on multilayer perceptron artificial neural networks. This 3D vectorial holography allows the lensless reconstruction of a 3D vectorial holographic image with an ultrawide viewing angle of 94° and a high diffraction efficiency of 78%, necessary for floating displays. The results provide an artificial intelligence–enabled holographic paradigm for harnessing the vectorial nature of light, enabling new machine learning strategies for holographic 3D vectorial fields multiplexing in display and encryption.

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<![CDATA[Super-resolution nanoscopy by coherent control on nanoparticle emission]]> https://www.researchpad.co/article/elastic_article_15372 Super-resolution nanoscopy based on wide-field microscopic imaging provided high efficiency but limited resolution. Here, we demonstrate a general strategy to push its resolution down to ~50 nm, which is close to the range of single molecular localization microscopy, without sacrificing the wide-field imaging advantage. It is done by actively and simultaneously modulating the characteristic emission of each individual emitter at high density. This method is based on the principle of excited state coherent control on single-particle two-photon fluorescence. In addition, the modulation efficiently suppresses the noise for imaging. The capability of the method is verified both in simulation and in experiments on ZnCdS quantum dot–labeled films and COS7 cells. The principle of coherent control is generally applicable to single-multiphoton imaging and various probes.

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<![CDATA[Fully stabilized multi-TW optical waveform synthesizer: Toward gigawatt isolated attosecond pulses]]> https://www.researchpad.co/article/elastic_article_15365 A stable 50-mJ three-channel optical waveform synthesizer is demonstrated and used to reproducibly generate a high-order harmonic supercontinuum in the soft x-ray region. This synthesizer is composed of pump pulses from a 10-Hz repetition-rate Ti:sapphire pump laser and signal and idler pulses from an infrared two-stage optical parametric amplifier driven by this pump laser. With full active stabilization of all relative time delays, relative phases, and the carrier-envelope phase, a shot-to-shot stable intense continuum harmonic spectrum is obtained around 60 eV with pulse energy above 0.24 μJ. The peak power of the soft x-ray continuum is evaluated to be beyond 1 GW with a 170-as transform limit duration. We found a characteristic delay dependence of the multicycle waveform synthesizer and established its control scheme. Compared with the one-color case, we experimentally observe an enhancement of the cutoff spectrum intensity by one to two orders of magnitude using three-color waveform synthesis.

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<![CDATA[Steering valley-polarized emission of monolayer MoS<sub>2</sub> sandwiched in plasmonic antennas]]> https://www.researchpad.co/article/elastic_article_15042 Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, making it appealing to exploit valleytronic and optoelectronic applications at the nanoscale. Here, we demonstrate that a chiral plasmonic antenna consisting of two stacked gold nanorods can modulate strongly valley-polarized photoluminescence (PL) of monolayer MoS2 in a broad spectral range at room temperature. The valley-polarized PL of the MoS2 using the antenna can reach up to ~47%, with approximately three orders of PL magnitude enhancement within the plasmonic nanogap. Besides, the K and K′ valleys under opposite circularly polarized light excitation exhibit different emission intensities and directivities in the far field, which can be attributed to the modulation of the valley-dependent excitons by the chiral antenna in both the excitation and emission processes. The distinct features of the ultracompact hybrid suggest potential applications for valleytronic and photonic devices, chiral quantum optics, and high-sensitivity detection.

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<![CDATA[Generation of multiple ultrastable optical frequency combs from an all-fiber photonic platform]]> https://www.researchpad.co/article/Nd0586391-d8b0-459f-81aa-1158600e4a4a

A telecommunication optical fiber can stabilize the comb-line frequencies of ultrashort pulse lasers to the quadrillionth level.

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<![CDATA[Four-wave mixing of topological edge plasmons in graphene metasurfaces]]> https://www.researchpad.co/article/N3e5b3352-8705-493d-9b5e-bb322490e321

It is demonstrated that net optical gain can be achieved via topologically protected four-wave mixing in a graphene metasurface.

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<![CDATA[Three dimensions, two microscopes, one code: Automatic differentiation for x-ray nanotomography beyond the depth of focus limit]]> https://www.researchpad.co/article/N1d2efadb-cbfa-4f30-95e1-dd1efa7e8bfb

We demonstrate the ability to reconstruct 3D objects beyond the depth of focus limit.

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<![CDATA[Two-photon quantum interference and entanglement at 2.1 μm]]> https://www.researchpad.co/article/Nc035750d-350a-4f67-a8fd-e22649ddad8e

Our results show a viable route to free-space quantum-secured communication in an unexplored atmospheric transparency window.

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<![CDATA[Terahertz quantum sensing]]> https://www.researchpad.co/article/N2606b85e-b5ed-4529-8e10-4bb9e9737625

Quantum sensing enables the measurement of sample properties in the terahertz frequency range by detecting visible photons.

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<![CDATA[Direct Kerr frequency comb atomic spectroscopy and stabilization]]> https://www.researchpad.co/article/N1a829f62-d4fa-48d2-a266-5498db0168e1

Orthogonal control of both degrees of freedom of a Kerr comb soliton allows high-precision atomic spectroscopy and stabilization.

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<![CDATA[How Can Phytoplankton Pigments Be Best Used to Characterize Surface Ocean Phytoplankton Groups for Ocean Color Remote Sensing Algorithms?]]> https://www.researchpad.co/article/N63e13cf1-730b-4762-810d-15dc971439a3

Abstract

High‐performance liquid chromatography (HPLC) remains one of the most widely applied methods for estimation of phytoplankton community structure from ocean samples, which are used to create and validate satellite retrievals of phytoplankton community structure. HPLC measures the concentrations of phytoplankton pigments, some of which are useful chemotaxonomic markers for phytoplankton groups. Here, consistent suites of HPLC phytoplankton pigments measured on global surface water samples are compiled across spatial scales. The global dataset includes >4,000 samples from every major ocean basin and representing a wide range of ecological regimes. The local dataset is composed of six time series from long‐term observatory sites. These samples are used to quantify the potential and limitations of HPLC for understanding surface ocean phytoplankton groups. Hierarchical cluster and empirical orthogonal function analyses are used to examine the associations between and among groups of phytoplankton pigments and to diagnose the main controls on these associations. These methods identify four major groups of phytoplankton on global scales (cyanobacteria, diatoms/dinoflagellates, haptophytes, and green algae) that can be identified by diagnostic biomarker pigments. On local scales, the same methods identify more and different taxonomic groups of phytoplankton than are detectable in the global dataset. Notably, diatom and dinoflagellate pigments group together on global scales, but dinoflagellate marker pigments always separate from diatoms on local scales. Together, these results confirm that HPLC pigments can be used for satellite algorithm quantification of no more than four phytoplankton groups on global scales, but can provide higher resolution for local‐scale algorithm development and validation.

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<![CDATA[Direct observation of glucose fingerprint using in vivo Raman spectroscopy]]> https://www.researchpad.co/article/N1ac158da-dc05-4fc1-8e4f-1f5e6bd91de5

Noninvasive optical sensor can measure blood glucose levels based on the glucose Raman signal from in vivo skin.

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<![CDATA[Multidimensional entanglement transport through single-mode fiber]]> https://www.researchpad.co/article/N008067ea-6e36-40b9-aa2d-8a81bfb8f4ff

This work suggests a new approach to multidimensional entanglement transport through conventional single-mode fiber.

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<![CDATA[Polymer-fiber-coupled field-effect sensors for label-free deep brain recordings]]> https://www.researchpad.co/article/N12f161cb-ce31-436b-989e-fa44b0a6dffa

Electrical recording permits direct readout of neural activity but offers limited ability to correlate it to the network topography. On the other hand, optical imaging reveals the architecture of neural circuits, but relies on bulky optics and fluorescent reporters whose signals are attenuated by the brain tissue. Here we introduce implantable devices to record brain activities based on the field effect, which can be further extended with capability of label-free electrophysiological mapping. Such devices reply on light-addressable potentiometric sensors (LAPS) coupled to polymer fibers with integrated electrodes and optical waveguide bundles. The LAPS utilizes the field effect to convert electrophysiological activity into regional carrier redistribution, and the neural activity is read out in a spatially resolved manner as a photocurrent induced by a modulated light beam. Spatially resolved photocurrent recordings were achieved by illuminating different pixels within the fiber bundles. These devices were applied to record local field potentials in the mouse hippocampus. In conjunction with the raster-scanning via the single modulated beam, this technology may enable fast label-free imaging of neural activity in deep brain regions.

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<![CDATA[Picosecond-resolution phase-sensitive imaging of transparent objects in a single shot]]> https://www.researchpad.co/article/N18907721-50d4-417e-aea3-7575e4e301d4

Integration of dark-field microscopy into compressed ultrafast photography enables 1 THz real-time imaging of transparent objects.

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<![CDATA[Focusing light inside live tissue using reversibly switchable bacterial phytochrome as a genetically encoded photochromic guide star]]> https://www.researchpad.co/article/Na2964bdf-7853-4ff3-894d-8e36521be67a

A genetically encoded photochromic guide star is used for focusing light inside live tissue by wavefront shaping.

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<![CDATA[A minimally invasive lens-free computational microendoscope]]> https://www.researchpad.co/article/Nb1db4367-4a80-418c-9f8d-17d30a2821a2

A distal lensless microendoscope is developed to enable minimally invasive imaging with wide field of view and digital refocusing.

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