Holographic Interference Patterns Research Articles

Deep-learning based 3D birefringence image generation using 2D multi-view holographic images

Refractive index stands as an inherent characteristic of a material, allowing non-invasive exploration of the three-dimensional (3D) interior of the material. Certain materials with different refractive indices produce a birefringence phenomenon in which incident light is split into two polarization components when it passes through the materials. Representative birefringent materials appear in calcite crystals, liquid crystals (LCs), biological tissues, silk fibers, polymer films, etc. If the internal 3D shape of these materials can be visually expressed through a non-invasive method, it can greatly contribute to the semiconductor, display industry, optical components and devices, and biomedical diagnosis. This paper introduces a novel approach employing deep learning to generate 3D birefringence images using multi-viewed holographic interference images. First, we acquired a set of multi-viewed holographic interference pattern images and a 3D volume image of birefringence directly from a polarizing DTT (dielectric tensor tomography)-based microscope system about each LC droplet sample. The proposed model was trained to generate the 3D volume images of birefringence using the two-dimensional (2D) interference pattern image set. Performance evaluations were conducted against the ground truth images obtained directly from the DTT microscopy. Visualization techniques were applied to describe the refractive index distribution in the generated 3D images of birefringence. The results show the proposed method’s efficiency in generating the 3D refractive index distribution from multi-viewed holographic interference images, presenting a novel data-driven alternative to traditional methods from the DTT devices.

High-throughput microplastic assessment using polarization holographic imaging

Microplastic (MP) pollution has emerged as a global environmental concern due to its ubiquity and harmful impacts on ecosystems and human health. MP assessment has therefore become increasingly necessary and common in environmental and experimental samples. Microscopy and spectroscopy are widely employed for the physical and chemical characterization of MPs. However, these analytical methods often require time-consuming pretreatments of samples or expensive instrumentation. In this work, we develop a portable and cost-effective polarization holographic imaging system that prominently incorporates deep learning techniques, enabling efficient, high-throughput detection and dynamic analysis of MPs in aqueous environments. The integration enhances the identification and classification of MPs, eliminating the need for extensive sample preparation. The system simultaneously captures holographic interference patterns and polarization states, allowing for multimodal information acquisition to facilitate rapid MP detection. The characteristics of light waves are registered, and birefringence features are leveraged to classify the material composition and structures of MPs. Furthermore, the system automates real-time counting and morphological measurements of various materials, including MP sheets and additional natural substances. This innovative approach significantly improves the dynamic monitoring of MPs and provides valuable information for their effective filtration and management.

Computer‐Generated Holographic Nanoprinting

AbstractMetasurface‐assisted nanoprinting is usually enabled by spectrum‐modulation and/or polarization‐modulation at the subwavelength scale. The spectrum‐modulated nanoprint works under unpolarized white‐light and requires the minimalist observation conditions, but it can hardly modulate light brightness; the polarization‐modulated nanoprint can continuously control light brightness, but it requires complex and precise polarization control both at the input and output ends to decode a nanoprinting image. In this study, computer‐generated holographic nanoprinting is designed and experimentally demonstrated, enabled by Pancharatnam–Berry phase modulation of light, which has both the advantages of the two types of nanoprintings while avoiding their disadvantages. Specifically, a general platform is built to implement single‐channel/multichannel/color nanoprinting in a holography way, which presents its unique characteristics like incoherent light illumination, arbitrary brightness modulation, polarization insensitivity, and zero‐dispersion. A periodic phase is further attached to the target object wave during the holographic interference pattern generation, and the reconstructed nanoprinting image only appears in the zero‐order diffraction direction, thus making the information delivery safer. This study can empower advanced research on metasurface‐based nanoprinting, which can find its markets in ultracompact image‐display, data storage, information multiplexing, and many other related fields.

Photoelectron holography in strong-field tunneling ionization by a spatially inhomogeneous field

Photoelectron holography in strong-field tunneling ionization is an efficient way to probe the structures and the ultrafast dynamics information of atoms and molecules. Manipulating the process of photoelectron holography is important for its application. Here, we study theoretically strong-field photoelectron holography in the spatially inhomogeneous field by solving the time-dependent Schr\"odinger equation. Our results show that the returning energy of the rescattering electron is greatly enhanced in the spatially inhomogeneous field, and the holographic interference pattern can be separated from other types of interference in the photoelectron momentum distribution. Moreover, our results show that the time window of tunneling ionization wherein the electron could be driven back to induce holography is broadened in the inhomogeneous field. These properties are beneficial for the application of photoelectron holography in probing the atomic and molecular structures and dynamics. The origin for these properties is analyzed with the classical trajectory model.

Large‐Scale Multiplexed Azopolymer Gratings with Engineered Diffraction Behavior

AbstractThe diffraction of polychromatic light from periodic superficial structures is often responsible for the structural colors observed in Nature. Similarly, engineered microtextures fabricated on metallic or dielectric surfaces can be used to design diffracted optical patterns with desired shapes and colors. To this aim, advanced diffraction gratings with exceptional design and functionality are continuously proposed, and new fabrication methods follow to stay abreast with the improving design capabilities. Multiplexed surface reliefs, acting as complex gratings with tunable diffraction behavior, can be readily produced on films of azobenzene containing materials by exposing the surface to controlled sequences of holographic interference patterns. This work fully investigates, both theoretically and experimentally, the use of light‐induced surface relief on azopolymers for the realization of large‐scale multiplexed gratings with optimized diffraction performances. The reconfigurable diffraction gratings able to diffract polychromatic light in the same direction with controllable relative color intensities by tuning exposure parameters in a switchable two‐beam interference setup are designed and fabricated. The results can be generalized to more complex diffractive devices, usable in emerging display application areas.

Efficient coding of experimental holograms using speckle denoising

Lossy compression for Experimental Holograms (EH) and Computer-Generated Holograms (CGH) using standardized coding solutions is a highly efficient process provided that these solutions can be applied to the object plane. This compression efficiency reveals to be more relevant in CGH. Speckle noise mainly affects reconstructed EH, and to less extent reconstructed CGH. In the current work, the reduction of speckle noise of EH is proposed to improve the coding efficiency of the hologram compression scheme. The compression scheme defines a base layer where a 2D version of the object is coded with an image codec standard. When speckle noise reduction is performed before any compression, efficient compression is obtained for both CGH and EH. Since speckle noise reduction is performed only on amplitude data, without affecting the phase information of the reconstructed hologram, it is still possible to render 3D features such as depth map, multi-view or to recover holographic interference patterns for further 3D visualization.

Taking snapshots of a moving electron wave packet in molecules using photoelectron holography in strong-field tunneling ionization* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874163, 11604108, and 11604388), the Program for HUST Academic Frontier Youth Team, and the Fundamental Research Funds for the Central Universities, China (HUST No. 2017KFXKJC002).

Coherent superposition of electronic states induces attosecond electron motion in molecules. We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrödinger equation. In the obtained photoelectron momentum distribution, an intriguing bifurcation structure appears in the strong-field holographic interference pattern. We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state: the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient. Thus, this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules.

Reconfigurable Holographic Metasurface Aided Wideband OFDM Communications Against Beam Squint

The future sixth-generation wireless communications are expected to realize an intelligent network of low powered and high throughput transmissions. In response to such demands, the reconfigurable holographic metasurface (RHS) is evolving into a promising solution owing to its flexible beam steering capability with low power and hardware costs. Unlike traditional phased antenna arrays with independent phase shifters, the RHS can generate desired beams by radiation amplitude control of the reference wave propagating along the metasurface. This so-called holographic interference technique enables an ultra-thin, small-sized planar antenna structure, which is suitable for integrated implementation without any complex phase-shifting or power-division circuits. In this paper, we consider an RHS-aided wideband communication system with an RHS-equipped base station. We aim to maximize the achievable data rate via joint digital beamforming (DBF) and holographic beamforming (HBF). To defeat the beam squint loss brought by the frequency-selective nature, we leverage the additivity of holographic interference patterns to design a novel amplitude control algorithm for solving the HBF subproblem, which contributes to our proposed joint DBF and HBF scheme. Simulation results validate the effectiveness of the proposed scheme against the beam squint issue in terms of the achievable rate.

Spiral-like holographic structures: Unwinding interference carpets of Coulomb-distorted orbits in strong-field ionization

We unambiguously identify, in experiment and theory, a previously overlooked holographic interference pattern in strong-field ionization, dubbed "the spiral", stemming from two trajectories for which the binding potential and the laser field are equally critical. We show that, due to strong interaction with the core, these trajectories are optimal tools for probing the target \textbf{after} ionization and for revealing obfuscated phases in the initial bound states. The spiral is shown to be responsible for interference carpets, formerly attributed to direct above-threshold ionization trajectories, and we show the carpet-interference condition is a general property due to the field symmetry.

Hardware implementations of computer-generated holography: a review

Computer-generated holography (CGH) is a technique to generate holographic interference patterns. One of the major issues related to computer hologram generation is the massive computational power required. Hardware accelerators are used to accelerate this process. Previous publications targeting hardware platforms lack performance comparisons between different architectures and do not provide enough information for the evaluation of the suitability of recent hardware platforms for CGH algorithms. We aim to address these limitations and present a comprehensive review of CGH-related hardware implementations.

Electromagnetically induced holographic imaging using monolayer graphene.

Graphene exhibits remarkable optical and electronic properties when interacts with electromagnetic field. These properties play a vital role in a broad range of applications, such as, optical communication, optical storage, biomedical imaging and security purposes. Based on electromagnetically induced grating (EIG), we study lensless holographic imaging via quantized energy levels of two-dimensional (2D) monolayer graphene model. We observe that by exploiting electromagnetically induced grating (EIG), holographic interference patterns via electromagnetically induced classical holographic imaging (EICHI) and, non locally, electromagnetically induced quantum holographic imaging (EIQHI) can be obtained in the infrared range (THz) of the spectrum. We notice that for EIQHI one can obtain image magnification using monolayer graphene via manipulation of certain controllable parameters. The scheme provides an experimentally viable option for the classical and quantum mechanical holographic imaging and possibilities for the design of graphene-based quantum mechanical devices which can have many applications.

Holographic interferences in strong-field ionization beyond the dipole approximation: The influence of the peak and focal-volume-averaged laser intensities

In strong-field ionization interferences between electron trajectories create a variety of interference structures in the final momentum distributions. Among them, the interferences between electron pathways that are driven directly to the detector and the ones that rescatter significantly with the parent ion lead to holography-type interference patterns that received great attention in recent years. In this work, we study the influence of the magnetic field component onto the holographic interference pattern, an effect beyond the electric dipole approximation, in experiment and theory. The experimentally observed nondipole signatures are analyzed via quantum trajectory Monte Carlo simulations. We provide explanations for the experimentally demonstrated asymmetry in the holographic interference pattern and its non-uniform photoelectron energy dependence as well as for the variation of the topology of the holography-type interference pattern along the laser field direction. Analytical scaling laws of the interference features are derived, and their direct relation to either the focal volume averaged laser intensities, or to the peak intensities are identified. The latter, in particular, provides a direct access to the peak intensity in the focal volume.

The Investigation of Photonic Band Gap of 2D Multi-fold Photonic Quasicrystals

Two dimensional photonic quasicrystals (PQCs) with different rotational symmetries are constructed based on holographic interference patterns. The photonic band gap (PBG) are obtained by calculating the transmission and reflection spectra based on the finite element method (FEM). The maximum PBG of different PQCs is obtained and investigated by considering the same dielectric constant and different fill factors. All the simulation settings are the same except for the structure itself in this process. The results show that 10-fold quasicrystal exhibit better band gap richness than the others. This may provide a reference to select appropriate quasicrystal structures for photonic devices.

Photonic bandgap properties of two dimensional photonic quasicrystals with multiple complex structures

Abstract Two dimensional photonic quasicrystals (PQCs) with different rotational symmetries are constructed based on holographic interference patterns. Their photonic bandgap (PBG) properties are obtained by using finite element method (FEM) to calculate the transmission and reflection spectra with different directions. The maximum gap-midgap ratio among different dielectric constant contrast and fill factor is given for all the PQCs to compare their abilities to produce bandgaps. The results show that 10-fold (five beams interference) and 12-fold quasicrystals are easier to form bandgaps than others. This may provide a reference to select appropriate quasicrystal structures for photonic devices and optimize device performance.

Holographic interferences in photoelectron spectra: different approaches

We perform a theoretical study of the holographic structures in photoelectron spectra for ionization of hydrogen atoms induced by short laser pulses. To elucidate the nature of the holographic structures present in the momentum distributions of photoelectrons, we use several quantum approximations, such as the strong field and Coulomb–Volkov approximations up to second order, as well as semiclassical Monte Carlo simulations. In a single-cycle pulse, we eliminate the intracycle interference from the spectra isolating the holographic structure formed in the photoionization process. We probe the different approaches and analyze the role of electron–core interaction numerically by solving the time dependent Schrodinger equation. We show that the two-step semiclassical model of Shvetsov-Shilovski et al. [Phys. Rev. A 94, 013415 (2016)] fully considers the effect of the Coulomb potential on the electron dynamics and semiclassical phase reproducing the holographic structure in full quantum calculations. Contrarily, perturbative quantum (strong field and Coulomb–Volkov) and semiclassical (quantum trajectory Monte Carlo) methods account only partially for some of the characteristics of the holographic interference pattern.

Holographic representation: Hologram plane vs. object plane

Digital holography allows the recording, storage and subsequent reconstruction of both amplitude and phase of the light field scattered by an object. This is accomplished by recording interference patterns that preserve the properties of the original object field essential for 3D visualization, the so-called holograms.Digital holography refers to the acquisition of holograms with a digital sensor, typically a CCD or a CMOS camera, and to the reconstruction of the 3D object field using numerical methods.In the current work, the different representations of digital holographic information in the hologram and in the object planes are studied. The coding performance of the different complex field representations, notably Amplitude-Phase and Real-Imaginary, in both the hologram plane and the object plane, is assessed using both computer generated and experimental holograms. The HEVC intra main coding profile is used for the compression of the different representations in both planes, either for experimental holograms or computer generated holograms.The HEVC intra compression in the object plane outperforms encoding in the hologram plane. Furthermore, encoding computer generated holograms in the object plane has a larger benefit than the same encoding over the experimental holograms. This difference was expected, since experimental holograms are affected by a larger negative influence of speckle noise, resulting in a loss of compression efficiency.This work emphasizes the possibility of holographic coding on the object plane, instead of the common encoding in the hologram plane approach. Moreover, this possibility allows direct visualization of the Object Plane Amplitude in a regular 2D display without any transformation methods. The complementary phase information can easily be used to render 3D features such as depth map, multi-view or even holographic interference patterns for further 3D visualization depending on the display technology.

High-order photoelectron holography in the midinfrared-wavelength regime

We study the dynamical photoelectron holography of an excited hydrogen atom with a strong midinfrared laser field using numerical solutions of the three-dimensional time-dependent Schrodinguer equation. A clear holographic interference pattern of first and high order (hologram) is recorded in the two-dimensional (2D) momentum distribution of the photoelectron. The patterns are well reproduced by additional quantitative calculations based on the Lippmann-Schwinger equation. Here, the high-order interference effect is linked to the multsicattering of low-momentum electrons driven by the midinfrared laser field prior to ejection. The phenomenon manifests by low-momentum structures in 2D momentum distributions and is found to be sensitive to the change of the optical carrier-envelope phase (CEP). By analyzing the temporal evolution of the buildup of the hologram, we show that this sensitivity results from the birth time of the continuum wave packet with an offset in time during the subcycle dynamics, thus encoding information about the ionization mechanism which is mapped into the CEP-resolved 2D momentum distributions and angle-resolved photoelectron spectra. It is indeed an indicator that the ejected electrons exhibit a memory of their birth-time. These findings suggest that the CEP-resolved photoelectron holography serves as a tool for a direct measurement of attosecond dynamics. Furthermore, the effects due to such multiple scattering electron paths can be used to design new atom interferometers to highlight mechanisms that require higher accuracy.

Local distortions revealed by neutron holography inSnCd0.0026alloy

Local distortions of the ideal periodic structure in crystals around impurity atoms play an important role in various physical properties of materials. The aim of this study was to investigate the static distortions around cadmium impurity atoms in a ${\text{SnCd}}_{0.0026}$ single crystal using atomic resolution neutron holography technique. The cadmium nucleus was used as an inside detector to measure the holographic interference pattern from which the three-dimensional (3D) atomic arrangement of tin nuclei around the cadmium impurities was reconstructed. Detailed analysis of the reconstructed image revealed the 3D static displacements of Sn atoms around the impurity. It was found that the crystal structure contracts around the cadmium impurity atom and the displacements tend to transform the crystal to the $\ensuremath{\alpha}$ phase. The local contraction of the lattice was used to explain the slower phase transformation to $\ensuremath{\alpha}$-Sn phase when Cd impurity atoms are present. The study shows the ability of neutron holography to measure 3D displacements around impurities which can be used, e.g., to understand the mechanisms that block the phase transformations in the presence of impurities.

Isotropic Holographic Metasurfaces for Dual‐Functional Radiations without Mutual Interferences

The dual‐functional and/or multifunctional devices have huge fascinations and prospects to conveniently integrate complex systems with low costs. However, most of such devices are based on anisotropic media or anisotropic structures. Here, a new method is proposed to design planar dual‐functional devices using an isotropic holographic metasurface, in which two different functions are written on the same holographic interference pattern with no mutual coupling. When the metasurface is excited by two orthogonally ported sources, the corresponding dual functions can be controlled by the object waves, which are not affected by each other due to suppression of mutual interference. The proposed metasurface is composed of subwavelength‐scale isotropic metallic patches on a grounded dielectric. In this specific design, double‐beam and double‐polarization radiate devices are realized independently by the orthogonal excitations. Based on the theoretical analysis, scanning radiate beams that are only controlled by frequency with different performances under orthogonal polarizations are demonstrated. To the best of our knowledge, this is the first time for actualizing dual‐functional devices using isotropic textures. Full‐wave simulations and experimental results in the microwave frequencies are presented to validate the proposed theory and confirm the corresponding physical phenomena.

Electromagnetically induced holographic imaging in hybrid artificial molecule.

We propose two schemes of holographic imaging with an object that has no any macro structure itself. The tunable electromagnetically induced grating (EIG) is such a kind of object. We obtain an EIG based on the periodically modulated strong susceptibility in a three-level ladder-type hybrid artificial molecule, which is comprised of a semiconductor quantum dot and a metal nanoparticle coupled via the Coulomb interaction. The holographic interference pattern is detected either directly in the way of classical holographic imaging with a coherent field being the imaging light, or indirectly and nonlocally in the way of two-photon coincidence measurement with a pair of entangled photons playing the role of imaging light. This work provides a practical prototype of electromagnetically induced transparency-based holographic solid-state devices for all-optical classical and quantum information processing.