Holographic Diffraction Research Articles

Establishment of Theoretically Guided Understanding for Magneto‐Optical Interactions through Ferromagnetic Fluids in Uniform, Static Magnetic Field

Prior magneto‐optical transmission models through ferrofluids are limited by oversimplifications which hinder accuracy and generalizability. To overcome this challenge, this study models the magnetic field effect on the magneto‐optical transmission through hematite ferrofluid using the method of invariant embedding. Optical coherence tomography (OCT) is used to extract the changes in the refractive index, enabling a discovery of a magnetodielectric effect for the hematite ferrofluid. To establish a basis for control and understanding, the influence of the magnetic field on the spatial transmission profile at different wavelengths, optical propagation lengths, and the effect of variation of each size parameter on the optical transmission have been investigated. Further parametric studies allowed finding out an analogy to nonuniform, cascade, volume holographic diffraction gratings, which is crucial for a wide range of optical and bioimaging applications. Compared to the experimental results, the presented model achieves 99% accuracy over the wavelength range (300–1100) nm under uniform static magnetic field (0–6.5) mT. Besides, the conspicuous lead of evidentiary understanding of magneto‐optical interactions with magnetic fluids, the structural milestones of the model can be further utilized to model similar challenging constructs in complex media. The innumerable applications of study extend to involve communication engineering, biomedical, optical, and security applications.

Robust Carbon‐Dot Optical Disks for Orthogonal Amplitude‐Polarization Encryption Storage

AbstractHigh‐capacity steganography is crucial for the secure exchange of massive information. Exploring orthogonally optical recording can significantly improve encryption levels. However, due to the lack of robust media, the hidden data are easy to be cracked or destructed. Herein, carbon dots have the switchable memory function between optical transmittance and polarization state after receiving excitation power adjustment is discovered. A large‐area carbon‐based disk is further constructed which is measured to resist the high‐temperature damage at 423 K for more than 405 h and is estimated to remain stable at room‐temperature (301 K) beyond 2341 years. With the alternated arrangement of the dual functional carbon dots at one region of the disk, only by using an amplitude‐type holographic diffraction key can the polarized pattern be correctly read out. The ultra‐high secure encryption strategy also puts a bright way to the applications of 3D image hiding, permanent data preservation, and anti‐counterfeiting labels.

Research of light diffraction on electrically controlled multiplexed multilayer inhomogeneous holographic diffraction structures based on the photopolymerizing compositions with nematic liquid crystals

We presented the developed analytical model of optical radiation diffraction on multiplexed multilayer inhomogeneous diffraction structures formed by the holographic method in photopolymerizing compositions with nematic liquid crystals having smooth optical heterogeneity in the thickness of the layers. By numerical calculation, it was shown that when using an applied electric field with different polarities to the diffraction layers, as well as varying the azimuth of the polarization of the reading beam, the angular selectivity of the diffracted beam can be transformed with a significant shift in angular selectivity, which makes it possible to increase the spectral bandwidth by 4 times compared to conventional multilayer diffraction structures.

Fully programmable holographic diffraction grating for NIR synthetic spectra generation in correlation spectroscopy

Correlation spectroscopy is a powerful analytical tool for gaseous species detection, with improved sensitivity and enhanced selectivity. The application in the field of this spectroscopic technique, for remote sensing purposes, has long been prevented due to the necessity to equip the instrument with a reference ‘cell’ containing an actual sample of the target molecules to perform correlation measurements. A new photonic chip, based on LNOI (lithium niobate on insulator) substrates, has been developed and tested by applying MEOS (micro electro optical system) micromachining techniques. The novel photonic chip allows to dynamically generate synthetic spectra of in principle any chemical species detectable in the transparency range of LNOI (350 nm – 5500 nm wavelength). The synthetic spectrum is generated by producing a well-defined holographic phase map in the active layer of the LNOI substrate, by applying through an array of driving electrodes a calculated voltage distribution, thus rendering the photonic chip fully programmable even in real-time. The developed photonic chip is therefore able to replace the classical sample cell and can be also used to act as a reference signal modulator, as requested in a correlation spectrometer. In this work, a description of the developed technology is reported together with some preliminary results obtained in different experimental conditions.

High Refractive Index, Low Birefringence Holographic Materials via the Homopolymerization of 1,2-Dithiolanes.

High refractive index, low birefringence photopolymers were created via the radical-mediated, ring opening homopolymerization of 1,2-dithiolane functionalized monomers and were subsequently evaluated as holographic recording media. This investigation systematically characterized the reaction kinetics, thermodynamics, and volume shrinkage of the 1,2-dithiolane homopolymerization as well as the optical transparency, refractive index, birefringence, and holographic performance of multifunctional 1,2-dithiolane functionalized monomers and their resultant polymers. Real-time kinetic and thermodynamic analyses of a monofunctional 1,2-dithiolane monomer, lipoic acid methyl ester (LipOMe), indicated rapid monomer conversion, exceeding 90% in 60 s, with an overall enthalpy of reaction of 18 ± 1 kJ/mol. The ring-opening polymerization resulted in low shrinkage (10.6 ± 0.3 cm3/mol dithiolane) and a significant bulk refractive index increase (0.030 ± 0.003). The resulting photopolymers exhibited high optical transparency, minimal haze, and negligible birefringence, suggesting the potential of 1,2-homopolymers as optical materials. To further explore the specific capabilities for use as high-performance holographic recording applications, several multifunctional monomers were synthesized with the ethanedithiol lipoic acid monomer (EDT-Lip2) selected for experimentation. Holographic diffraction gratings written using this monomer achieved a peak-to-mean refractive index modulation of 0.008 with minimal haze and birefringence.

Holographic surface relief diffraction gratings made of hydrogels for direct label-free biosensing of IgGs

This work describes the development of a label-free (LF) biosensing platform for the direct detection of targets based on diffractive structures fabricated with acrylamide-based hydrogels biofunctionalized with proteins and antibodies. Hydrogels containing Bovine Serum Albumin protein (BSA) with different crosslinking degrees were synthesized and characterized to find the optimal conditions for the suitable fabrication of surface relief gratings (SRGs). The bioavailability of BSA-functionalized hydrogels for the specific recognition of anti-BSA antibodies was verified by fluorescence detection. After the hydrogel-based SRG fabrication, diffraction efficiency measures at two different laser wavelengths were used for the direct LF detection of anti-BSA antibodies. The limit of detection in the sub mg L−1 range was read. Additionally, SRGs were prepared with hydrogels biofunctionalized with anti-rabbit antibodies for the direct detection of IgGs from rabbit serum, obtaining similar analytical performance without the necessity of labeling or applying amplification strategies.

Studying the Diffraction of Light on Electrically Controlled Multiplexed Multilayer Inhomogeneous Holographic Diffraction Structures Based on Photopolymerizing Compositions with Nematic Liquid Crystals

Studying the Diffraction of Light on Electrically Controlled Multiplexed Multilayer Inhomogeneous Holographic Diffraction Structures Based on Photopolymerizing Compositions with Nematic Liquid Crystals

A Holographic Broadband Achromatic Metalens

AbstractMetalens with nanostructured optical elements are designed to control wavefront shaping at the wavelength‐scale thickness. However, most metalens still suffer from large chromatic aberrations due to phase dispersion, limiting their wide applications for multiple wavelengths. Here, avoiding complex resonant designs or multiple‐layer nanostructures, a simple broadband achromatic metalens by holographic diffraction in the visible spectrum is demonstrated. The hyperbolic phase distributions of multiple discrete wavelengths within a shared aperture and fabricate a broadband achromatic diffractive metalens by flexible direct‐laser‐writing technique is randomly interleaved. The designed polarization‐insensitive metalens modulate the light field by changing the height of the artificial neuron phase units to achieve average focusing efficiencies of 55% in the visible spectrum. This holographic design concept can pave the way to expand achromatic metalenses to multiple spectra.

Diffraction Characteristics of Multiplexed Multilayer Inhomogeneous Holographic Diffraction Structures in Photopolymerizing Compositions with Liquid Crystals

Diffraction Characteristics of Multiplexed Multilayer Inhomogeneous Holographic Diffraction Structures in Photopolymerizing Compositions with Liquid Crystals

Continuous-wave terahertz in-line holographic diffraction tomography with the scattering fields reconstructed by a physics-enhanced deep neural network

Diffraction tomography is a promising, quantitative, and nondestructive three-dimensional (3D) imaging method that enables us to obtain the complex refractive index distribution of a sample. The acquisition of the scattered fields under the different illumination angles is a key issue, where the complex scattered fields need to be retrieved. Presently, in order to develop terahertz (THz) diffraction tomography, the advanced acquisition of the scattered fields is desired. In this paper, a THz in-line digital holographic diffraction tomography (THz-IDHDT) is proposed with an extremely compact optical configuration and implemented for the first time, to the best of our knowledge. A learning-based phase retrieval algorithm by combining the physical model and the convolution neural networks, named the physics-enhanced deep neural network (PhysenNet), is applied to reconstruct the THz in-line digital hologram, and obtain the complex amplitude distribution of the sample with high fidelity. The advantages of the PhysenNet are that there is no need for pretraining by using a large set of labeled data, and it can also work for thick samples. Experimentally with a continuous-wave THz laser, the PhysenNet is first demonstrated by using the thin samples and exhibits superiority in terms of imaging quality. More importantly, with regard to the thick samples, PhysenNet still works well, and can offer 2D complex scattered fields for diffraction tomography. Furthermore, the 3D refractive index maps of two types of foam sphere samples are successfully reconstructed by the proposed method. For a single foam sphere, the relative error of the average refractive index value is only 0.17%, compared to the commercial THz time-domain spectroscopy system. This demonstrates the feasibility and high accuracy of the THz-IDHDT, and the idea can be applied to other wavebands as well.

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications.

Computational holographic ghost diffraction.

Since the paradigm shift in 2009 from pseudo-thermal ghost imaging (GI) to computational GI using a spatial light modulator, computational GI has enabled image formation via a single-pixel detector and thus has a cost-effective advantage in some unconventional wave bands. In this Letter, we propose an analogical paradigm known as computational holographic ghost diffraction (CH-GD) to shift ghost diffraction (GD) from classical to computational by using self-interferometer-assisted measurement of field correlation functions rather than intensity correlation functions. More than simply "seeing" the diffraction pattern of an unknown complex volume object with single-point detectors, CH-GD can retrieve the diffracted light field's complex amplitude and can thus digitally refocus to any depth in the optical link. Moreover, CH-GD has the potential to obtain the multimodal information including intensity, phase, depth, polarization, and/or color in a more compact and lensless manner.

Transmission functions of transmissive multilayer inhomogeneous holographic photopolymer liquid crystal diffraction structures

A new analytical model of diffraction of quasimonochromatic light beams on spatially inhomogeneous multilayer diffraction structures formed in photopolymer material with nematic liquid crystals having smooth optical inhomogeneity in the thickness of layers is presented. It is shown that when an applied electric field isapplied to diffraction layers containing a photopolymer composition with a high proportion of liquid crystalline component, a transformation of the selective response with a significant shift in angular selectivity occurs

Continuous-wave terahertz holographic diffraction tomography based on multiple scattering forward model

Terahertz waves exhibit the great potential applications due to their particular properties. Also, diffraction tomography (DT) is an effective way to detect the internal three-dimensional structure of the sample. The terahertz DT (THz-DT) is an attractive and growing technique. However, when the samples to be measured are with complex internal structures or high refractive index contrast, the multiple scattering effect is a challenging problem, and even becomes more serious because of the large wavelength of the THz wave, which makes the first-order Born/Rytov approximation hardly to be satisfied and brings severe distortions to the reconstruction results. In this paper, the continuous-wave THz-DT based on digital holography is presented including the multiple scattering effect, which can further improve the reconstruction fidelity. The multiple scattering forward model is introduced to describe the propagation process of the THz wave inside the sample, and the modified split-step beam propagation method is presented, which evolves from its original version as one of the main forward models for the visible optical DT. Both the reconstruction accuracy and computation efficiency are achieved higher. Then, the simulations and experiments of THz-DT are performed, and three-dimensional reconstruction results with more fine structures are obtained by applying the correspondingly developed optimization-based nonlinear inverse scattering algorithm. To our best knowledge, it is the first time to apply the multiple scattering forward model into THz DT to improve the reconstruction fidelity. Besides, the capacity of the proposed method to enable sparse-angle reconstruction is also demonstrated by reducing the number of rotation angles, which is particularly important for real-time measurement applications.

Optical properties of planar plasmon active surfaces modified with gold nanostars

The article discusses the experimental and theoretical results of studying the optical properties for planar quartz surfaces modified with gold nanostars using Surface-Enhanced Raman Spectroscopy (SERS). Surfaces functionalized with nanoparticles, prototypes of optical sensors, have been obtained. It is shown that the obtained experimental Raman signal enhancement from the dye rhodamine 6G (R6G) can be at least order 104. The paper presents the results of calculation, synthesis and study of the optical and morphological properties of such structures. A complex method for creating and evaluating the optical properties of planar nanostructures and evaluating their optical properties is proposed. The method includes the approaches based on mathematical modeling using finite differences in the time domain (FDTD - Finite-Difference Time-Domain) evaluating electromagnetic field strengths near the surfaces of star-shaped gold nanoparticles in colloidal solutions and on a silicon surface. During the simulation, we studied such parameters as the particle size, the wavelength of the exciting radiation, and the dependence of the effective amplification of the electromagnetic field on the morphological parameters of the star. The theoretical approach to the calculation of such structures is shown to be promising for the subsequent chemical synthesis described in the article and the study of optical properties. In this paper, a theoretical calculation of the parameters of the electric field and optical properties is carried out near star-shaped nanoparticles of varying sizes. These parameters were calculated by the finite difference method in the time domain. The task included finding the optimal sizes of nanoparticles as well as varying the thickness of the surface layers in order to obtain the maximum scattering values and further use of similar structures in SERS experiments. Also, within the framework of this work, syntheses of star-shaped nanoparticles was carried out, their optical and morphological properties were studied, quartz surfaces were functionalized with nanoparticles, and sensor prototypes were created in order to further assess the Raman signal amplification. Based on the results of mathematical modeling, the optimal sizes for the synthesis of star-shaped NPs were determined. Synthesis of NPs was carried out by a chemical method using seeds. To carry out the experimental part, SERS spectra were obtained using Centaur U spectrometer (OOO NanoScanTechnology, Russia). The spectrometer was equipped with three different laser sources: 632.8 nm He-Ne laser (17 mW), 532 nm and 473 nm DPSS lasers (45 mW). During the experiment, a He-Ne laser with λ = 632 nm and DPSS laser with λ = 532 nm were used to match the excitation of the plasmon maximum for the nanostars. The optical scheme of the spectrometer included an Olympus BX41 microscope (Olympus, Japan) with a 100× objective (NA 0.9) for positioning the beam and collecting scattered photons. The monochromator of the spectrometer had a focal length of 800 mm. A holographic diffraction grating of 300 gr/mm, and was equipped with a 1024×256 pixel thermoelectric cooled CCD detector (Andor Tech., UK). As a result of the paper, surfaces functionalized by nanoparticles were obtained prototypes of optical sensors. It is shown that the experimental gain of the Raman signal can be no less than 104 times. The presented data will serve as the basis for obtaining the required sizes of nanostars in the methods of the controlled chemical synthesis of colloidal nanoparticles. The results presented in the article can be applied to the development of biocompatible and highly sensitive optical sensors based on the effect of Raman scattering of light.

Fabrication of 5D Fresnel Lenses via Additive Manufacturing.

The consistent developments in additive manufacturing (AM) processes are revolutionizing the fabrication of 3-dimensional (3D) parts. Indeed, 3D printing processes are prompt, parallel, material efficient, and cost-effective, along with their capabilities to introduce added dimensions to the computer-aided design (CAD) models. Notably, 3D Printing is making progressive developments to fabricate optical devices such as regular lenses, contact lenses, waveguides, and more recently, Fresnel lenses. But extended functionalities of these optical devices are also desirable. Therefore, we demonstrate masked stereolithography (MSLA) based fabrication of five-dimensional (5D) Fresnel lenses by incorporating color-change phenomena (4th dimension) using thermochromic powder that changes color in response to external temperature variations (25-36 °C). The holographic diffraction effect (5th dimension) is produced by imprinting a diffraction grating during the printing process. Optical focusing performance for the 5D printed lenses has been evaluated by reporting achievable focal length, with <2 mm average deviation, without postprocessing in 450-650 nm spectral range. However, in the near IR region (850-980 nm), the average deviation was around 11.5 mm. Enhanced optical properties along with surface quality have been reported. Thus, MSLA process can fabricate optical components with promising applications in the fields of sensing and communication.

Highly Sensitive Photopolymer for Holographic Data Storage Containing Methacryl Polyhedral Oligomeric Silsesquioxane.

Herein, via introducing eight methacryl polyhedral oligomeric silsesquioxane (Ma-POSS), we dramatically enhance the holographic performance of phenanthraquinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer with excellent characteristics of high sensitivity, high diffraction efficiency, and neglectable volume shrinkage for holographic data storage, the photosensitivity, diffraction efficiency, and volume shrinkage reaching 1.47 cm/J, ∼75%, and ∼0.09%, respectively. Ma-POSS here dramatically enhances the photosensitivity ∼5.5 times, diffraction efficiency more than 50%, and suppressed the volume shrinkage over 4 times. Further analysis reveals that Ma-POSS obviously increased the molecular weight by grafting PMMA to be a star-shaped macromolecule. And the residual C=C of POSS–PMMA dramatically increased the photosensitivity. Moreover, the star-shaped POSS–PMMA acting as a plasticizer dramatically enhances the mechanical properties and so reduces the photoinduced volume shrinkage of PQ/PMMA. Finally, by the use of the POSS–PMMA/PQ in a collinear holography system, it appeared to be promising for a fast but low bit error rate in holographic information storage. The current study thence has not only successfully synthesized photopolymer materials with potential for highly sensitive holographic storage applications but also investigated the microphysical mechanism of the impact of Ma-POSS on the holographic properties of PQ/PMMA photopolymer and clarified the thermal- and photoreaction processes of the POSS–PMMA/PQ photopolymer.

Diffraction gratings for spectral devices [Review

Subject of study. This review is intended to acquaint the reader with various types of diffraction gratings and technologies for fabricating them. Method. An information search on the topic, systematization, and analysis are performed. Main results. This paper briefly discusses the areas of application and classification of spectral devices and shows the variety of problems that can be solved by means of spectral devices and that impose various requirements on diffraction gratings. It lists the main characteristics of diffraction gratings used in spectral devices and specifies the stages of their improvement. It discusses classical reflective diffraction gratings—plane (profiled and laminar) and concave. It describes the principles involved in obtaining holographic diffraction gratings and their advantages over ruled ones. It devotes special attention to concave holographic gratings with aberration correction, shows how they are classified, and briefly describes methods of optimizing the parameters of gratings that operate in monochromator systems with simple rotation and flat-field spectrographs with correction of defocusing, astigmatism, and meridional coma, as well as various methods of recording gratings in nonhomocentric beams to expand their correction possibilities. Ruled analogs of holographic gratings are used in a number of cases. It is pointed out that foreign and Russian firms that batch-produce diffraction gratings of the types described here completely satisfy the requirements of the batch-producers of spectral devices. The features of using volume phase gratings in spectral devices are considered, and it is pointed out that, even though these gratings are distinguished by high efficiency, their angular and spectral selectivity have inhibited these gratings from being widely applied in spectral devices. However, there have been active studies in recent years on expanding the regions in which volume phase gratings are used: new system solutions, recording materials, and recording methods have been proposed. Trends to create diffraction elements that combine various functions (cross gratings and grisms) are pointed out. New technologies are proposed for fabricating diffraction gratings: ruled gratings—pendulum-type ruling engines, gratings that reflect with high diffraction efficiency in an expanded wavelength range—“efficiency-achromatization” or double-blaze technologies and volume phase gratings—ultrafast laser inscription and profiled diffraction gratings that operate in the x-ray region—electron-beam lithography, to miniature spectral devices—microelectronic mechanical systems technology used in electronics, composites—concepts of a composite volume phase diffraction grating recorded by integrating several elementary fields. The Conclusion evaluates the modern level and points out development trends. Practical significance. The material presented here can be useful in the development of spectral apparatus.

Towards practical holographic coherent diffraction imaging via maximum likelihood estimation.

A new algorithmic framework is developed for holographic coherent diffraction imaging (HCDI) based on maximum likelihood estimation (MLE). This method provides superior image reconstruction results for various practical HCDI settings, such as when data is highly corrupted by Poisson shot noise and when low-frequency data is missing due to occlusion from a beamstop apparatus. This method is also highly robust in that it can be implemented using a variety of standard numerical optimization algorithms, and requires fewer constraints on the physical HCDI setup compared to current algorithms. The mathematical framework developed using MLE is also applicable beyond HCDI to any holographic imaging setup where data is corrupted by Poisson shot noise.

Continuous-Wave Terahertz Holographic Diffraction Tomography Based on Multiple Scattering Forward Model

Continuous-Wave Terahertz Holographic Diffraction Tomography Based on Multiple Scattering Forward Model