1,721,154 research outputs found
Photocatalytic Vicinal Aminopyridylation of Methyl Ketones by a Double Umpolung Strategy
No full text© 2020 Wiley-VCH GmbHA photocatalytic double umpolung strategy for the vicinal aminopyridylation of ketones was developed using pyridinium N−N ylides. The inversion of the polarity of the pyridinium N−N ylides by single-electron oxidation successfully enables radical-mediated 1,3-dipolar cycloadditions with enolsilanes formed in situ from ketones, followed by homolytic cleavage of the N−N bond. Intriguingly, the nucleophilic amino and electrophilic pyridyl groups in the ylides can be installed at the nucleophilic α-position and electrophilic carbonyl carbon, respectively, which are typically inaccessible by their innate polarity-driven reactivity. This method accommodates a broad scope, and the utility was further demonstrated by the late-stage functionalization of complex biorelevant molecules. Moreover, the strategy can be successfully applied to enamides11sciescopu
Fourier holographic endoscopy for imaging continuously moving objects
No full textCoherent fiber bundles are widely used for endoscopy, but conventional approaches require distal optics to form an object image and acquire pixelated information owing to the geometry of the fiber cores. Recently, holographic recording of a reflection matrix enables a bare fiber bundle to perform pixelation-free microscopic imaging as well as allows a flexible mode operation, because the random core-to-core phase retardations due to any fiber bending and twisting could be removed in situ from the recorded matrix. Despite its flexibility, the method is not suitable for a moving object because the fiber probe should remain stationary during the matrix recording to avoid the alteration of the phase retardations. Here, we acquire a reflection matrix of a Fourier holographic endoscope equipped with a fiber bundle and explore the effect of fiber bending on the recorded matrix. By removing the motion effect, we develop a method that can resolve the perturbation of the reflection matrix caused by a continuously moving fiber bundle. Thus, we demonstrate high-resolution endoscopic imaging through a fiber bundle, even when the fiber probe changes its shape along with the moving objects. The proposed method can be used for minimally invasive monitoring of behaving animals.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement11Nsciescopu
Preferential coupling of an incident wave to reflection eigenchannels of disordered media
Full text linkLight waves incident to a highly scattering medium are incapable of penetrating deep into the medium due to the multiple scattering process. This poses a fundamental limitation to optically imaging, sensing, and manipulating targets embedded in opaque scattering layers such as biological tissues. One strategy for mitigating the shallow wave penetration is to exploit eigenchannels with anomalously high transmittance existing in any scattering medium. However, finding such eigenchannels has been a challenging task due to the complexity of disordered media. Moreover, it is even more difficult to identify those eigenchannels from the practically relevant reflection geometry of measurements. In this Letter, we present an iterative wavefront control method that either minimizes or maximizes the total intensity of the reflected waves. We proved that this process led to the preferential coupling of incident wave to either low or high-reflection eigenchannels, and observed either enhanced or reduced wave transmission as a consequence. Since our approach is free from prior characterization measurements such as the recording of transmission matrix, and also able to keep up with sample perturbation, it is readily applicable to in vivo applications. Enhancing light penetration will help improving the working depth of optical sensing and treatment techniques.6611Nsciescopu
‐Aminopyridinium Salts
No full textThrough the formation of an electron donor-acceptor (EDA) complex, strain-release aminopyridylation of [1.1.1]propellane with N-aminopyridinium salts as bifunctional reagents enabled the direct installation of amino and pyridyl groups onto bicyclo[1.1.1]pentane (BCP) frameworks in the absence of an external photocatalyst. The robustness of this method to synthesize 1,3-aminopyridylated BCPs under mild and metal-free conditions is highlighted by the late-stage modification of structurally complex biorelevant molecules. Moreover, the strategy was extended to P-centered and CF3 radicals for the unprecedented incorporation of such functional groups with pyridine across the BCP core in a three-component coupling. This practical method lays the foundation for the straightforward construction of new valuable C4-pyridine-functionalized BCP chemical entities, thus significantly expanding the range of accessibility of BCP-type bioisosteres for applications in drug discovery.11Nsciescopu
Control of randomly scattered surface plasmon polaritons for multiple-input and multiple-output plasmonic switching devices
Full text linkAbstractMerging multiple microprocessors with high-speed optical networks has been considered a promising strategy for the improvement of overall computation power. However, the loss of the optical communication bandwidth is inevitable when interfacing between optical and electronic components. Here we present an on-chip plasmonic switching device consisting of a two-dimensional (2D) disordered array of nanoholes on a thin metal film that can provide multiple-input and multiple-output channels for transferring information from a photonic to an electronic platform. In this device, the surface plasmon polaritons (SPPs) generated at individual nanoholes become uncorrelated on their way to the detection channel due to random multiple scattering. We exploit this decorrelation effect to use individual nanoholes as independent antennas, and demonstrated that more than 40 far-field incident channels can be delivered simultaneously to the SPP channels, an order of magnitude improvement over conventional 2D patterned devices.</jats:p
Deep optical imaging within complex scattering media
No full text© 2020, Springer Nature Limited.Optical imaging has had a central role in elucidating the underlying biological and physiological mechanisms in living specimens owing to its high spatial resolution, molecular specificity and minimal invasiveness. However, its working depth for in vivo imaging is extremely shallow, and thus reactions occurring deep inside living specimens remain out of reach. This problem originates primarily from multiple light scattering caused by the inhomogeneity of tissue obscuring the desired image information. Adaptive optical microscopy, which minimizes the effect of sample-induced aberrations, has to date been the most effective approach to addressing this problem, but its performance has plateaued because it can suppress only lower-order perturbations. To achieve an imaging depth beyond this conventional limit, there is increasing interest in exploiting the physics governing multiple light scattering. New approaches have emerged based on the deterministic measurement and/or control of multiple-scattered waves, rather than their stochastic and statistical treatment. In this Review, we provide an overview of recent developments in this area, with a focus on approaches that achieve a microscopic spatial resolution while remaining useful for in vivo imaging, and discuss their present limitations and future prospects
© 2020 Springer Nature Limited11Nsciescopu
Selective Pump Focusing on Individual Laser Modes in Microcavities
No full textWe demonstrate selective pump focusing for highly isolated single-mode lasers in microdisk and microring cavities, and achieve lasing action from a microdisk cavity underneath a scattering medium. The spatial profile of the pumping light evolves by an iterative feedback process and is optimized to maximize the field overlap with a selected cavity mode. The high order of mode selectivity and high resolving power are obtained in a multimode cavity in the presence of significant modal overlaps. As a result of the adaptive optical pumping, we successfully achieve the efficient energy transfer to a microdisk underneath a random scattering medium and observe lasing action through the scattering medium. We believe that our selective pumping procedure will pave the way for the development of low-threshold, single-mode nanolasers embedded in various materials.© 2018 American Chemical Societ
Near-field transmission matrix microscopy for mapping high-order eigenmodes of subwavelength nanostructures
No full text© 2020, The Author(s).As nanoscale photonic devices are densely integrated, multiple near-field optical eigenmodes take part in their functionalization. Inevitably, these eigenmodes are highly multiplexed in their spectra and superposed in their spatial distributions, making it extremely difficult for conventional near-field scanning optical microscopy (NSOM) to address individual eigenmodes. Here, we develop a near-field transmission matrix microscopy for mapping the high-order eigenmodes of nanostructures, which are invisible with conventional NSOM. At an excitation wavelength where multiple modes are superposed, we measure the near-field amplitude and phase maps for various far-field illumination angles, from which we construct a fully phase-referenced far- to near-field transmission matrix. By performing the singular value decomposition, we extract orthogonal near-field eigenmodes such as anti-symmetric mode and quadruple mode of multiple nano-slits whose gap size (50 nm) is smaller than the probe aperture (150 nm). Analytic model and numerical mode analysis validated the experimentally observed modes11sci
Wave propagation dynamics inside a complex scattering medium by the temporal control of backscattered waves
No full textShaping the wavefront of an incident wave to a complex scattering medium has demonstrated interesting possibilities, such as sub-diffraction wave focusing and light energy delivery enhancement. However, wavefront shaping has mainly been based on the control of transmitted waves that are inaccessible in most realistic applications. Here, we investigate the effect of maximizing the backscattered waves at a specific flight time on wave propagation dynamics and energy transport. We find both experimentally and numerically that the maximization at a short flight time focuses waves on the particles constituting the scattering medium, leading to the attenuation of the wave transport. On the contrary, maximization at a long flight time induces constructive wave interference inside the medium and thus enhances wave transport. We provide a theoretical model that explains this interesting transition behavior based on wave correlation. Our study provides a fundamental understanding of the effect of wave control on wave dynamics inside scattering medium. © 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.11Nsciescopu
Single-shot multiple-depth macroscopic imaging by spatial frequency multiplexing
No full text© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.We present a low-coherence interferometric imaging system designed for 3-dimensional (3-D) imaging of a macroscopic object through a narrow passage. Our system is equipped with a probe-type port composed of a bundle fiber for imaging and a separate multimode optical fiber for illumination. To eliminate the need for mechanical depth scanning, we employ a spatial frequency multiplexing method by installing a 2-D diffraction grating and an echelon in the reference arm. This configuration generates multiple reference beams, all having different path lengths and propagation directions, which facilitates the encoding of different depth information in a single interferogram. We demonstrate the acquisition of 9 depth images at the interval of 250 µm for a custom-made cone and a plaster teeth model. The proposed system minimizes the need for mechanical scanning and achieves a wide range of depth coverage, significantly increasing the speed of 3-D imaging for macroscopic objects.11Nsciescopu
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