Optics express最新文献

Stroboscopic nanoscale imaging with free electron laser light is revolutionizing our understanding of fast dynamics in heterogeneous systems. The short wavelength of X-ray and extreme ultraviolet radiation makes it possible to achieve nanoscale resolution, while resonance with atomic transitions gives access to electronic and magnetic degrees of freedom. Here, we report on our implementation of a recently developed imaging method, randomized probe imaging, at a free electron laser. The advantage of randomized probe imaging over existing methods is its compatibility with extended and strongly scattering samples. Our implementation delivers robust single-shot reconstructions at up to a full-pitch resolution of 400 nm over a field of view with a 40 µm diameter. We also demonstrate single-shot imaging of magnetic domain structures using circular dichroism at resonance, paving the way to future time-resolved studies of magnetic dynamics, shock physics, and the dynamics of collective electronic phases.

The exponential growth of communication networks and internet technologies poses severe threats to information security, prompting significant interest in optical encryption as a promising physical-layer solution. Herein, a terahertz encryption framework utilizing an image as an information carrier is presented. In this scheme, information is encoded into a specific Optical Transfer Function implemented via a metasurface, which modulates the carrier's angular spectrum. This architecture uniquely decouples information from the physical hardware, enabling flexible data transmission and digital processing, offering advantages absent in traditional metasurface-based schemes. Security is further reinforced by polarization-dependent decoding, where information retrieval is strictly confined to specific polarization channels. This scheme provides a versatile and robust solution for terahertz encryption.

Utilizing the generalized multiparticle Mie theory, we address the scattering of an electromagnetic plane wave from a one dimensional array of parallel gyrotropic core-dielectric shell cylinders. Specifically, we examine InSb core-Ge shell cylinders subjected to magnetic fields below 2.3 T. We show that the undesired grating diffraction orders can be suppressed via the interference of electric and magnetic multipoles. The grating offers exciting opportunities for terahertz beam steering: By applying appropriate static magnetic fields, almost perfect transmission, almost perfect reflection, almost perfect absorption, large-angle negative refraction and large-angle negative reflection of terahertz waves are achievable. Indeed, deflection angles as large as 158^∘ are realizable.

Non-contact quantitative characterization of nanostructures on transparent substrates is important for applications spanning flexible displays, photovoltaic devices, and advanced optical coatings. Conventional ellipsometric techniques, while widely used, often face limitations such as interference from backside reflection and insufficient spatial resolution for nanoscale mapping. In this study, we introduce coherent Fourier ellipsometry (CFE) as what we believe to be a novel approach enabling precise parameter estimation of thin films on transparent substrates with high spatial resolution. The core principle of CFE involves encoding multi-angle reflection coefficients for both s- and p-polarized light into spatially resolved reflected light field generated by a tightly focused beam. This rich optical information, extracted through quantitative analysis of phase and polarization diversity, facilitates inverse modeling and accurate determination of the sample's physical properties. We rigorously validated CFE's accuracy through comprehensive numerical simulation and experimental measurements of ITO films on transparent glasses. Owing to its high spatial resolution, non-invasiveness, and suitability for nanoscale probing, we believe CFE emerges as a powerful and versatile tool for thin film characterization on transparent substrates in optical and semiconductor industries.

Accurately retrieving the lateral velocity of distant, non-cooperative targets under photon-starved conditions has remained a longstanding challenge, as conventional imaging or tracking methods often fail in the absence of stable illumination or resolvable features. We present a single-photon light detection and ranging (LiDAR) interferometric scheme that actively illuminates the target and measures its motion-induced optical path difference variations across spatially separated receivers. A complete theoretical framework is developed, which establishes the system's sensitivity limit and predicts the minimum detectable photon number. Simulations and experiments demonstrate that the method achieves micron-level spatial resolution and millimeter-per-second velocity precision with as few as ∼200 detected photons per single measurement, and remains effective over kilometer-scale free-space links. The approach is robust to non-cooperative targets, enabling high-precision velocity sensing in extremely low-light environments. By integrating with single-photon ranging, it can deliver full 3D velocity vectors, extending the operational envelope of LiDAR for space surveillance, collision avoidance, and precision motion sensing.

The outermost electron in a F^- ion experiences a much weaker, short-range induced force, which has attracted widespread attention. By using an improved negative-ion quantum-trajectory Monte Carlo (NI-QTMC) model, which is a semiclassical method, we theoretically investigate how a short-range Coulomb potential affects photoelectron momentum distributions (PMDs) of F^- ions in a few-cycle infrared (IR) laser pulse. The PMDs present a series of concentric above-threshold detachment (ATD) rings emanating from the center and the recollision rings, which are consistent with those obtained by the fully quantum approach, demonstrating the feasibility of the NI-QTMC model. The results show that the short-range Coulomb potential primarily influences the rescattering photodetachment rather than the direct photodetachment of the F^- ion. The short-range Coulomb potential in Newton's equations plays an important role in the formation of the recollision rings. It can be demonstrated that, owing to the absence of Coulomb focusing in the short-range Coulomb potential, the variation of final longitudinal momentum with carrier envelope phase (CEP) is much weaker than that in the long-range Coulomb potential case. In addition, the short-range Coulomb potential can also influence the probability of electron emission in the forward and backward directions. Moreover, we can illustrate that the electrons emitted around θ = 90^∘ and θ = 270^∘ rarely change with the CEP in the case of the short-range Coulomb potential, which is related to the CEP-independent emission direction of rescattered electrons. Our results provide an analytical tool for investigating negative-ion photodetachment and broaden the scope of the short-range Coulomb potential in strong-field ionization.

This study explores how various display characteristics-such as chromatic gamut, peak luminance, color reproduction methods, and substrate grayscale-affect the diagnostic performance of the Computerized Color Vision Test (CCVT). Through both theoretical simulations and psychophysical experiments, the research examines the impact of these factors on test accuracy for color vision deficient (CVD) individuals. The findings highlight that perceptual-based color reproduction methods can improve test consistency across different display settings by reducing the impact of chromatic gamut, backlight luminance, and grayscale variations. These insights are essential for optimizing color reproduction settings, ultimately enhancing the clinical accuracy of CCVT across a range of display devices.

The shot-noise-limited sensitivity for detecting audio-frequency phase signals has garnered significant interest in both research and practical applications. This work presents a novel experimental setup that generates frequency-synthesized light with suppressed carrier and enhanced sidebands using an electro-optic intensity modulator (EOIM). When injected into a Mach-Zehnder interferometer (MZI), the EOIM-generated light not only enables phase-sensitive heterodyne locking to stabilize the relative phase of the MZI but also functions as a balanced heterodyne detector for audio-frequency phase measurements. By integrating these three key techniques into the MZI, phase detection sensitivity reaches the shot-noise limit across the audio-frequency band. This advancement holds promise for applications in gravitational wave detection, vacuum magnetic birefringence studies, spin-orbital interactions, material characterization, polarization microscopy, atomic magnetometry, and biomedical optics.

Bioluminescence tomography (BLT) is a promising molecular imaging modality with significant potential in preclinical research, enabling three-dimensional quantitative reconstruction of internal bioluminescent sources. However, the low absorption and severe photon scattering effects in biological tissues render the BLT inverse problem highly ill-conditioned, often leading to unstable and inaccurate reconstruction results. In this study, an adaptive orthogonal matching pursuit with group K-singular value decomposition (AOMP-GKSVD) algorithm is proposed within a dictionary learning framework. An adaptive sparsity estimation mechanism is incorporated into the sparse coding phase to infer the sparsity level from the measured data and the system matrix, thereby better capturing the intrinsic sparsity characteristics of bioluminescent sources. This overcomes the limitation of fixed sparsity settings in conventional OMP, enhancing reconstruction accuracy and robustness, while saving time and effort by eliminating the need for manual sparsity tuning under varying noise and source conditions. During the dictionary update phase, a grouping strategy based on a discretized tetrahedral mesh is employed, in which atoms are updated collectively at the group level, exploiting spatial adjacency to maintain coherence and efficiently reconstruct clustered source regions. The performance of AOMP-GKSVD was validated through a series of numerical simulations and a light source implantation experiment. The experimental results demonstrate that AOMP-GKSVD achieves superior performance in terms of localization accuracy, morphological recovery, and robustness, highlighting its potential to advance the practical application of BLT in preclinical optical molecular imaging.

We present the design and numerical analysis of an asymmetric bow-tie vertical-cavity surface-emitting laser (ABT-VCSEL) that enables PAM-2 direct modulation up to 100 GHz. The device concept relies on photon-photon resonance (PPR) between laterally coupled modes, triggered by a structural asymmetry introduced via a hollowed dielectric mirror. This approach avoids the need for asymmetric pumping and probing while ensuring strong modal coupling under uniform carrier injection. A dynamical in-house suite, combining field-carrier interaction, electromagnetic, and thermal problems, is developed and discussed to evaluate device performance under realistic conditions. The simulation results predict a 3-dB bandwidth up to 70 GHz with low modulation swing, and open eye diagrams at 100 GHz PAM-2 modulation and 70 GHz PAM-4 modulation. The proposed ABT-VCSEL concept shows robustness against geometrical variations and ambient temperature when proper cavity detuning is applied, making it a promising candidate for next-generation ultra-fast short-reach interconnects.