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Vol. 12 ， Issue 2 ， 2023
- Abstract：Principal component analysis (PCA), a common dimensionality reduction method, is introduced into SIM to identify the frequency vectors and pattern phases of the illumination pattern with precise subpixel accuracy, fast speed, and noise-robustness, which is promising for real-time and long-term live-cell imaging.
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Published：2024-04-28 - Abstract：Three-dimensional photoacoustic tomography synchronized with an electrocardiogram provides highly resolved images of a beating heart with optical absorption contrast and enables investigation of cardiovascular diseases in animal models.
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Published：2024-04-28
News & Views
- Abstract：Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfaces, nanoscale optical sensors, and many more, and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics. Here, we experimentally implement a novel strategy for dielectric nanophotonics: Resonant subwavelength localized confinement of light in air. We demonstrate that voids created in high-index dielectric host materials support localized resonant modes with exceptional optical properties. Due to the confinement in air, the modes do not suffer from the loss and dispersion of the dielectric host medium. We experimentally realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm (4.68 eV). Furthermore, we utilize the bright, intense, and naturalistic colours for nanoscale colour printing. Mie voids will thus push the operation of functional high-index metasurfaces into the blue and UV spectral range. The combination of resonant dielectric Mie voids with dielectric nanoparticles will more than double the parameter space for the future design of metasurfaces and other micro- and nanoscale optical elements. In particular, this extension will enable novel antenna and structure designs which benefit from the full access to the modal field inside the void as well as the nearly free choice of the high-index material for novel sensing and active manipulation strategies.
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Published：2024-04-28 - Abstract：Mapping red blood cells (RBCs) flow and oxygenation is of key importance for analyzing brain and tissue physiology. Current microscopy methods are limited either in sensitivity or in spatio-temporal resolution. In this work, we introduce a novel approach based on label-free third-order sum-frequency generation (TSFG) and third-harmonic generation (THG) contrasts. First, we propose a novel experimental scheme for color TSFG microscopy, which provides simultaneous measurements at several wavelengths encompassing the Soret absorption band of hemoglobin. We show that there is a strong three-photon (3P) resonance related to the Soret band of hemoglobin in THG and TSFG signals from zebrafish and human RBCs, and that this resonance is sensitive to RBC oxygenation state. We demonstrate that our color TSFG implementation enables specific detection of flowing RBCs in zebrafish embryos and is sensitive to RBC oxygenation dynamics with single-cell resolution and microsecond pixel times. Moreover, it can be implemented on a 3P microscope and provides label-free RBC-specific contrast at depths exceeding 600 µm in live adult zebrafish brain. Our results establish a new multiphoton contrast extending the palette of deep-tissue microscopy.
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Published：2024-04-28 - Abstract：Doping and blending strategies are crucial means to precisely control the excited states and energy level in conjugated molecular systems. However, effective models and platforms are rarely proposed to systematically explore the effects of the formation of trapped doped centers on heterogeneous structures, energy level and ultrafast photophysical process. Herein, for deeply understanding the impact of molecular doping in film energy levels and photoexcitation dynamics, we set a supramolecular N-B coordination composed by the conjugated molecules of pyridine functionalized diarylfluorene (host material), named as ODPF-Phpy and ODPF-(Phpy)2, and the molecule of tris(perfluorophenyl)borane (BCF) (guest material). The generation of the molecular-level coordination bond increased the binding energy of N atoms and tuned the band-gap, leading to a new fluorescent emission center with longer excitation wavelength and emission wavelength. The intermolecular Förster resonance energy transfer (FRET) in blending films make it present inconsistent fluorescent behaviors compared to that in solution. The charge transfer (CT) state of N-B coordinated compounds and the changed dielectric constant of blending films resulted in a large PL spectra red-shift with the increased dopant ratio, causing a wide-tunable fluorescent color. The excited state behaviors of two compounds in blending system was further investigated by the transient absorption (TA) spectroscopy. Finally, we found supramolecular coordination blending can effectively improve the films' photoluminescence quantum yield (PLQY) and conductivity. We believe this exploration in the internal coordination mechanisms would deepen the insights about doped semiconductors and is helpful in developing novel high-efficient fluorescent systems.
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Published：2024-04-28 - Abstract：Dispersion remains an enduring challenge for the characterization of wavelength-dependent transmission through optical multimode fiber (MMF). Beyond a small spectral correlation width, a change in wavelength elicits a seemingly independent distribution of the transmitted field. Here we report on a parametric dispersion model that describes mode mixing in MMF as an exponential map and extends the concept of principal modes to describe the fiber's spectrally resolved transmission matrix (TM). We present computational methods to fit the model to measurements at only a few, judiciously selected, discrete wavelengths. We validate the model in various MMF and demonstrate an accurate estimation of the full TM across a broad spectral bandwidth, approaching the bandwidth of the best-performing principal modes, and exceeding the original spectral correlation width by more than two orders of magnitude. The model allows us to conveniently study the spectral behavior of principal modes, and obviates the need for dense spectral measurements, enabling highly efficient reconstruction of the multispectral TM of MMF.
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Published：2024-04-28 - Abstract：RGB and CYMK are two major coloring schemes currently available for light colors and pigment colors, respectively. Both systems use letter-based color codes that require a large range of values to represent different colors. The problem is that these two systems are hard to use for manipulating any operations involving combinations of colors, and they lack the capacity for inter-changeability or unification. Based on prime number theory and Goldbach's conjecture, this study presents a universal color system (C235) using a number-based structure to encode, compute and unify all colors on a color wheel. The proposed C235 system offers a unified representation for the efficient encoding and effective manipulation of color. It can be applied to designing a high-rate LCD system and colorizing objects with multiple attributes and DNA codons, opening the door to manipulating colors and lights for even broader applications.
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Published：2024-04-28 - Abstract：The developing advances of microresonator-based Kerr cavity solitons have enabled versatile applications ranging from communication, signal processing to high-precision measurements. Resonator dispersion is the key factor determining the Kerr comb dynamics. Near the zero group-velocity-dispersion (GVD) regime, low-noise and broadband microcomb sources are achievable, which is crucial to the application of the Kerr soliton. When the GVD is almost vanished, higher-order dispersion can significantly affect the Kerr comb dynamics. Although many studies have investigated the Kerr comb dynamics near the zero-dispersion regime in microresonator or fiber ring system, limited by dispersion profiles and dispersion perturbations, the near-zero-dispersion soliton structure pumped in the anomalous dispersion side is still elusive so far. Here, we theoretically and experimentally investigate the microcomb dynamics in fiber-based Fabry-Perot microresonator with ultra-small anomalous GVD. We obtain 2/3-octave-spaning microcombs with ~10 GHz spacing, > 84 THz span, and > 8400 comb lines in the modulational instability (MI) state, without any external nonlinear spectral broadening. Such widely-spanned MI combs are also able to enter the soliton state. Moreover, we report the first observation of anomalous-dispersion based near-zero-dispersion solitons, which exhibits a local repetition rate up to 8.6 THz, an individual pulse duration < 100 fs, a span > 32 THz and > 3200 comb lines. These two distinct comb states have their own advantages. The broadband MI combs possess high conversion efficiency and wide existing range, while the near-zero-dispersion soliton exhibits relatively low phase noise and ultra-high local repetition rate. This work complements the dynamics of Kerr cavity soliton near the zero-dispersion regime, and may stimulate cross-disciplinary inspirations ranging from dispersion-controlled microresonators to broadband coherent comb devices.
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Published：2024-04-28 - Abstract：Ultrashort energetic terahertz (THz) pulses have created an exciting new area of research on light interactions with matter. For material studies in small laboratories, widely tunable femtosecond THz pulses with peak field strength close to MV cm−1 are desired. Currently, they can be largely acquired by optical rectification and difference frequency generation in crystals without inversion symmetry. We describe in this paper a novel scheme of THz pulse generation with no frequency tuning gap based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media, particularly diamond. We show that we could generate highly stable, few-cycle pulses with near-Gaussian spatial and temporal profiles and carrier frequency tunable from 5 to > 20 THz. They had a stable and controllable carrier-envelop phase and carried ~15 nJ energy per pulse at 10 THz (with a peak field strength of ~1 MV cm−1 at focus) from a 0.5-mm-thick diamond. The measured THz pulse characteristics agreed well with theoretical predictions. Other merits of the scheme are discussed, including the possibility of improving the THz output energy to a much higher level.
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Published：2024-04-28 - Abstract：Rabi oscillation is an elementary laser-driven physical process in atoms and artificial atoms from solid-state systems, while it is rarely demonstrated in molecules. Here, we investigate the bond-length-dependent Rabi oscillations with varying Rabi frequencies in strong-laser-field dissociation of H2+. The coupling of the bond stretching and Rabi oscillations makes the nuclei gain different kinetic energies while the electron is alternatively absorbing and emitting photons. The resulting proton kinetic energy spectra show rich structures beyond the prediction of the Floquet theorem and the well-accepted resonant one-photon dissociation pathway. Our study shows that the laser-driven Rabi oscillations accompanied by nuclear motions are essential to understanding the bond-breaking mechanism and provide a time-resolved perspective to manipulate rich dynamics of the strong-laser-field dissociation of molecules.
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Published：2024-04-28 - Abstract：High-power terahertz radiation was observed to be emitted from a gas jet irradiated by 100-terawatt-class laser pulses in the laser-wakefield acceleration of electrons. The emitted terahertz radiation was characterized in terms of its spectrum, polarization, and energy dependence on the accompanying electron bunch energy and charge under various gas target conditions. With a nitrogen target, more than 4 mJ of energy was produced at < 10 THz with a laser-to-terahertz conversion efficiency of ~0.15%. Such strong terahertz radiation is hypothesized to be produced from plasma electrons accelerated by the ponderomotive force of the laser and the plasma wakefields on the time scale of the laser pulse duration and plasma period. This model is examined with analytic calculations and particle-in-cell simulations to better understand the generation mechanism of high-energy terahertz radiation in laser-wakefield acceleration.
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Published：2024-04-28 - Abstract：Nanomaterials-based photoluminescence thermometry (PLT) is a new contact-free photonic approach for temperature sensing, important for applications ranging from quantum technology to biomedical imaging and diagnostics. Even though numerous new materials have been explored, great challenges and deficiencies remain that hamper many applications. In contrast to most of the existing approaches that use large ensembles of rare-earth-doped nanomaterials with large volumes and unavoidable inhomogeneity, we demonstrate the ultimate size reduction and simplicity of PLT by using only a single erbium-chloride-silicate (ECS) nanowire. Importantly, we propose and demonstrate a novel strategy that contains a self-optimization or "smart" procedure to automatically identify the best PL intensity ratio for temperature sensing. The automated procedure is used to self-optimize key sensing metrics, such as sensitivity, precision, or resolution to achieve an all-around superior PLT including several record-setting metrics including the first sensitivity exceeding 100% K−1 (~138% K−1), the highest resolution of 0.01 K, and the largest range of sensible temperatures 4–500 K operating completely within 1500–1800 nm (an important biological window). The high-quality ECS nanowire enables the use of well-resolved Stark-sublevels to construct a series of PL intensity ratios for optimization in infrared, allowing the completely Boltzmann-based sensing at cryogenic temperature for the first time. Our single-nanowire PLT and the proposed optimization strategy overcome many existing challenges and could fundamentally impact PL nano-thermometry and related applications such as single-cell thermometry.
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Published：2024-04-28 - Abstract：Soliton molecules (SMs) are stable bound states between solitons. SMs in fiber lasers are intensively investigated and embody analogies with matter molecules. Recent experimental studies on SMs formed by bright solitons, including soliton-pair, soliton-triplet or even soliton-quartet molecules, are intensive. However, study on soliton-binding states between bright and dark solitons is limited. In this work, the formation of such novel SMs in a fiber laser with near-zero group velocity dispersion (ZGVD) is reported. Physically, these SMs are formed because of the incoherent cross-phase modulation of light and constitute a new form of SMs that are conceptually analog to the multi-atom molecules in chemistry. Our research results could assist the understanding of the dynamics of large SM complexes. These findings may also motivate potential applications in large-capacity transmission and all-optical information storage.
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Published：2024-04-28 - Abstract：Conventional artificial intelligence (AI) machine vision technology, based on the von Neumann architecture, uses separate sensing, computing, and storage units to process huge amounts of vision data generated in sensory terminals. The frequent movement of redundant data between sensors, processors and memory, however, results in high-power consumption and latency. A more efficient approach is to offload some of the memory and computational tasks to sensor elements that can perceive and process the optical signal simultaneously. Here, we proposed a non-volatile photomemristor, in which the reconfigurable responsivity can be modulated by the charge and/or photon flux through it and further stored in the device. The non-volatile photomemristor has a simple two-terminal architecture, in which photoexcited carriers and oxygen-related ions are coupled, leading to a displaced and pinched hysteresis in the current-voltage characteristics. For the first time, non-volatile photomemristors implement computationally complete logic with photoresponse-stateful operations, for which the same photomemristor serves as both a logic gate and memory, using photoresponse as a physical state variable instead of light, voltage and memresistance. The polarity reversal of photomemristors shows great potential for in-memory sensing and computing with feature extraction and image recognition for neuromorphic vision.
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Published：2024-04-28 - Abstract：There are two primary types of photoreceptor cells in the human eye: cone cells and rod cells that enable color vision and night vision, respectively. Herein, inspired by the function of human visual cells, we develop a high-resolution perovskite-based color camera using a set of narrowband red, green, blue, and broadband white perovskite photodetectors as imaging sensors. The narrowband red, green, and blue perovskite photodetectors with color perceptions mimic long-, medium-, and short-wavelength cones cells to achieve color imaging ability. Also, the broadband white perovskite photodetector with better detectivity mimics rod cells to improve weak-light imaging ability. Our perovskite-based camera, combined with predesigned pattern illumination and image reconstruction technology, is demonstrated with high-resolution color images (up to 256 × 256 pixels) in diffuse mode. This is far beyond previously reported advanced perovskite array image sensors that only work in monochrome transmission mode. This work shows a new approach to bio-inspired cameras and their great potential to strongly mimic the ability of the natural eye.
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Published：2024-04-28 - Abstract：High-speed and high-resolution imaging of surface profiles is critical for the investigation of various structures and mechanical dynamics of micro- and nano-scale devices. In particular, recent emergence of various nonlinear, transient and complex mechanical dynamics, such as anharmonic vibrations in mechanical resonators, has necessitated real-time surface deformation imaging with higher axial and lateral resolutions, speed, and dynamic range. However, real-time capturing of fast and complex mechanical dynamics has been challenging, and direct time-domain imaging of displacements and mechanical motions has been a missing element in studying full-field structural and dynamic behaviours. Here, by exploiting the electro-optic sampling with a frequency comb, we demonstrate a line-scan time-of-flight (TOF) camera that can simultaneously measure the TOF changes of more than 1000 spatial coordinates with hundreds megapixels/s pixel-rate and sub-nanometre axial resolution over several millimetres field-of-view. This unique combination of performances enables fast and precise imaging of both complex structures and dynamics in three-dimensional devices and mechanical resonators.
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Published：2024-04-28
Original Articles
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