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Properly structuring materials at subwavelength scale allows for strong light-matter interaction, thereby enhancing near-field effects and engineering far-field scattering through intermodal interference. A majority of such effects are associated with plasmonics where electromagnetic waves created in the vicinity of metallic nanostructures is able to give rise to a variety of novel phenomena and fascinating applications. In the recent years, dielectric nanoparticles with high refractive index based on optically induced electric and magnetic Mie resonances attract a plethora of attention. In this rapidly developing field, dissipative loss in optical materials is considered one of the major challenges. Here, in this dissertation, we show that, counter-intuitively, it contributes positively to sub-wavelength scale light enhancement and confinement, and also improves scattering efficiency in the far field. In the first part of this dissertation, near field enhancement in dissipative dielectric antennas is demonstrated to be orders of magnitude higher than their lossless dielectric counterparts, which is particularly favorable in deep UV applications where metals are plasmonically inactive and transparent dielectrics always have low index. The loss facilitated field enhancement is the result of large material permittivity contrast and electric field discontinuity. These dissipative dielectric nanostructures can be easily achieved with a great variety of dielectrics at their Lorentz oscillation frequencies, thus having the potential to build a completely new material platform boosting light-matter interaction over broader frequency ranges, with advantages such as bio-compatibility, CMOS compatibility and harsh environment endurance. Additionally, manipulation of ultra-violet light through metasurface in the far field utilizing the silicon loss is then presented. We experimentally demonstrate Si metasurfaces working effectively over a broad band down to 290nm, with efficiencies comparable to plasmonic metasurface performance in the infrared regime. And for the first time, we show photolithography enabled by metasurface-generated ultraviolet holograms. We attribute such performance enhancement to the large scattering cross-sections of Si antennas in the ultraviolet range, which is adequately modeled via a circuit model. Our new platform will deepen our understanding of the role of material dissipation and introduce even more material options to broadband metaphotonic applications, including those in integrated photonics and holographic lithography technologies.Dynamically tunable far field with subwavlength nanostructures is always desired for practical applications. In the last section of this dissertation, we introduce a lithography free and field-programmable photonic metacanvas. Previous attempts of realizing such idea used micro-mechanical metamaterials or amorphous-crystalline phase transition materials, which are limited in terms of the functionalities, efficiency, cost, and high working temperature (> 600oC). It is much desired to reconfigure photonic devices in a fast, large-scale, cost-effective, reliable, and free-style way at or near room temperature. Here, we present a completely rewritable meta-canvas on which arbitrary photonic devices can be rapidly written, erased and rewritten. The writing is with a low-power (1 mW) continuous laser and the entire process stays below ~ 90oC. Using these devices we demonstrate dynamical manipulation of optical waves for light propagation, reconstruction and polarization. Such meta-canvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where a single photonic element can be field-programmed to deliver complex, system-level functionalities.

Transcranial ultrasound therapy has become a non-invasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multi-target transcranial ultrasound therapy is a better solution. At present, multi-target transcranial ultrasound therapy in small animals can only be achieved by the multi-transducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multi-target transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm × 10.08 mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full width at half maximum (FWHM) of the focal spots in y-direction were 2.15 and 2.27 mm, respectively, and in z-direction were 2.3 and 2.36 mm, respectively. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 mm and 6.0 mm, respectively. Finally, the multiple-target blood-brain barrier opening in rats' bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multi-target transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost.

Recently in nanophotonics, a rigorous evolution from passive to active metasurfaces has been witnessed. This advancement not only brings forward interesting physical phenomena but also elicits opportunities for practical applications. However, active metasurfaces operating at visible frequencies often exhibit low performance due to design and fabrication restrictions at the nanoscale. In this work, we demonstrate electrochemically controlled metasurfaces with high intensity contrast, fast switching rate, and excellent reversibility at visible frequencies. We use a conducting polymer, polyaniline (PANI), that can be locally conjugated on preselected gold nanorods to actively control the phase profiles of the metasurfaces. The optical responses of the metasurfaces can be in situ monitored and optimized by controlling the PANI growth of subwavelength dimension during the electrochemical process. We showcase electrochemically controlled anomalous transmission and holography with good switching performance. Such electrochemically powered optical metasurfaces lay a solid basis to develop metasurface devices for real-world optical applications.

Morphology measurement is essential for a better understanding of irregular particle dynamics. Digital holography of side scattering is applied to measure the morphology and 3D position of pulverized coal particles. The digital holographic recording of particle side scattering is modelled and the formula is verified by experiments. A side scattering holography system is established to record the hologram of pulverized coal particles. The hologram of particles with several scatterers has uneven chirp fringes which is mainly influenced by scatterer shape, while the hologram of particles with multiple scatterers is a superposition of single scatterer fringes with a speckle background which is influenced by both scatterer shape and location. The Moire pattern which appears easily in digital holography of side scattering is also analyzed. The proposed technique is validated by in-line holography and is proven to have an advantage in the identification of irregular particle morphological and surface features simultaneously.

Holography has been extensively studied as a vital method to tailor wavefronts of electromagnetic waves. Compared to conventional holography, metasurface-based holography generally presents the adv...

The diffraction of light by reflective holographic gratings in a layer placed between the coating and the substrate having refractive indices different from the average refractive index of the inserted layer is investigated. Significant differences between the reflection and transmission coefficients of the light diffracted on such a holographic grating with a change in the modulation amplitude of the refractive index of the layer, and the reflection and transmission coefficients of reflection gratings in matched structures are established. It is shown that at a large width of the layer in which the reflective holographic grating is located, there is a significant rotation of the plane of polarization of reflected and transmitted diffracted waves with a change in the modulation amplitude of the layer, caused by Fresnel reflection of light at the layer boundaries.

The paper presents a study of the formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors. The recording process of holographic gratings at the argon-laser radiation wave length 488 nm and the process of chemical etching that enables the formation of а relief holographic grating are analysed. The optimum conditions for the formation of diffraction gratings in films of arsenic sulfide As2S3 are defined. It is shown that at the 488 nm wave length of an argon laser the optimum exposure comes to ∼5–8 J/cm2. At the recording stage a quasi-phase (relief-phase) grating is formed, with the diffraction efficiency on the order of a few per cent. Etching of the exposed sample with a solution of NaOH alkali in deionised water and isopropanol makes it possible to increase considerably the relief depth and to improve the diffraction efficiency of a thin diffraction grating approximately up to 20 % for the red spectral region, and to approach the maximal value ∼34 % for the near infra-red region. The results of the study considered look promising for the creation of relief holographic gratings which are essential in present-day optical instrument building (production of spectral devices, holographic sights, and the like).

Sprays generated by atomization processes have been used in a wide range of fields. The size and spatial distribution of volumetric droplets in a spray are critical parameters in industrial applications. Astigmatic interferometric particle imaging (AIPI), an extension of the traditional interferometric particle imaging (IPI), is developed to simultaneously measure the size and 3D position of volumetric droplets in a sparse spray. Based on the generalized Huygens–Fresnel integral and the transfer matrix, the size and depth position of droplet can be respectively extracted from the fringe spacing and orientation of interferogram in AIPI. An AIPI setup is established to characterize droplets in a sparse spray generated by a nozzle with the AIPI calibration procedure adopted. The measured parameters by AIPI are compared with those obtained synchronously by digital inline holography, which is regarded as a standard measurement technique. Results show that the average deviation values of droplet size and depth position are respectively 3.8% and 6.8%. AIPI has been demonstrated with high accuracy in simultaneous 3D positions and size measurements.

Measuring the distribution, characteristics and dynamics of marine microscale plankton and other particulate matter is essential to understand the vertical flux of elements in the marine environment. Digital holographic microscopy is a powerful approach for measuring these and studying their 3-D trajectories in a relatively large observation volume. This article demonstrates a compact, in-line digital holographic microscope that allows large-volume and high-resolution recording of marine particles through combining a continuous wave laser and a short exposure CMOS camera with efficient global shutters. A resolution of better than 10 μm is demonstrated in air and the minimum distinguishable size of targets recorded in water is approximately 20 μm. The maximum volumetric throughput of the setup is 1904 mL/s. The microscope can take motion blur free holograms of particles moving at up to 490 mm/s in theory, and has been tested in the ∼200-mm/s flowing water. The orientation of the measured volume improves the ability of digital holography in profiling sinking rates and active vertical migration. The system was tested onboard a research vessel to record a range of live plankton and other particles. The motion of some samples, including the sinking motion and swimming motion, was analyzed using custom developed image processing software. The experimental results show that the combination of high resolution and a large volume over which motion of sparse-distribution particles can be tracked, can improve the ability to differentiate between different types of marine particle and identify behaviors of live plankton.

The purpose of this research is to increase the speed with which holographic optical tweezers (HOT) can individually assemble microscale particles for fabricating useful volumes of mechanical metamaterials in reasonable build times. HOT systems are unique among other additive manufacturing approaches in their ability to create true-3D structures with multiple materials, microscale features, and overhanging geometries. To scale up HOT-based fabrication, this research focuses on four primary goals: (1) scaling the number of particles that can be handled simultaneously using scanning holographic optical tweezers (SHOT), (2) developing efficient path planning and automation algorithms for efficiently delivering particles to their destinations within the fabricated structure, (3) modeling the dynamics of discretely-stepped optically-trapped particles to reliably handle them at high speeds, and (4) efficiently joining adjacent particles to produce a permanent structure. In addition, this work also demonstrates a proof-of-concept system that combines the HOT approach with the two-photon lithography approach, which allows for simultaneous fabrication and manipulation of microscale mechanisms in the same system for the first time. By improving the number and speed of particles that can be handled with the HOT approach, this work provides a promising path towards automated and scalable manufacturing of materials with extraordinary properties, such as microgranular lattices or microstructures with embedded strain energy.

We consider the problem of achieving high stability and linearity of phase liquid-crystal space-time light modulators, which are widely used for optical reconstruction of diffractive optical elements, including holograms. Modern high-resolution space-time light modulators one uses a digital signal addressing circuit, which leads to phase shift fluctuations during the frame. For the modern high-resolution phase liquid crystal space-time light modulator Santec SLM-200, the dependences of the phase shift on the level of the addressed signal and time from the beginning of the frame have been measured. Using the Santec SLM-200 light modulator, optical reconstruction of images from diffractive elements of different types was performed, their diffraction efficiency and the quality of the reconstructed images were evaluated. The values of the diffraction efficiency were obtained in the range of 3–10%; a sharp drop in the brightness of the reconstructed images is observed with distance from the optical axis in the plane of reconstruction.

Advances in electron microscopy have enabled visualizations of the three-dimensional (3D) atom arrangements in nano-scale objects. The observations are, however, prone to electron-beam-induced object alterations, so tracking of single atoms in space and time becomes key to unravel inherent structures and properties. Here, we introduce an analytical approach to quantitatively account for atom dynamics in 3D atomic-resolution imaging. The approach is showcased for a Co-Mo-S nanocrystal by analysis of time-resolved in-line holograms achieving ~1.5 Å resolution in 3D. The analysis reveals a decay of phase image contrast towards the nanocrystal edges and meta-stable edge motifs with crystallographic dependence. These findings are explained by beam-stimulated vibrations that exceed Debye-Waller factors and cause chemical transformations at catalytically relevant edges. This ability to simultaneously probe atom vibrations and displacements enables a recovery of the pristine Co-Mo-S structure and establishes, in turn, a foundation to understand heterogeneous chemical functionality of nanostructures, surfaces and molecules., The authors introduce an analytical approach for quantitative analysis of 3D atom dynamics during electron microscopy. They image a Co-Mo-S nanocrystal with 1.5 Å resolution, and observe chemical transformations caused by beam-stimulated vibrations.

Nowadays, the electromagnetic properties of artificial photonic materials can be well-tuned via designs over their composition and geometries. However, engineering the properties of artificial materials at the nanoscale is challenging and costly. Here we demonstrate a facile and low-cost method for fabricating large-area silver nanoparticle metasurfaces (AgNPMSs) by using the vectorial holography-mediated growth technique. The AgNPMS, which can be regarded as a hologram device, possesses excellent chiroptical properties. The vectorial holographic technique may open avenues for fabricating novel chiroptical metamaterials with large degrees of freedom, which can be further used for beam steering, photocatalysis, biosensing, etc.

In this paper, we present two approaches for recording a quasi-hologram on the steel surface by femtosecond laser pulses. The recording process is done by rotating the polarization of the laser beam by a half-wave plate or a spatial light modulator (SLM), so we can control the spatial orientation of the formed laser-induced periodic surface structures (LIPSS). Two different approaches are shown, which use vector and bitmap images to record the hologram. For the first time to our knowledge, we managed to record a hologram of a bitmap image by continuously adjusting the laser beam polarization by SLM during scanning. The developed method can substantially improve hologram recording technology by eliminating complex processing procedures, which can lead to increasing the fabrication speed and reducing the cost.

We report a wideband and polarization-/wide-angle insensitive metamaterial absorber based on a symmetry structure associated with surface mount resistors. The proposed structure consists of a periodic array of a top metal symmetry resonator loading with four lumped resistors and a continuous metal ground plane separated by a dielectric substrate of FR-4. A prototype of the proposed absorber is fabricated and measured, confirming a good agreement between the measurement and simulation results. The proposed absorber shows polarization-insensitive behavior and the absorption response in a frequency range from 8-18 GHz covering the entire X- and Ku- bands with an absorptivity above 80$\%$ for a wide incident angle up to 40$^{\circ }$ for both transverse electric and transverse magnetic polarizations. Compared with the reported broadband absorbers using lumped resistors, our proposed absorber exhibits excellent characteristics in terms of compact and simple structure, high relative absorption bandwidth, and polarization and wide-incident insensitivity. Therefore, this design shows promising potential for both X- and Ku-band applications.

In several phenomena in biology and industry, it is required to understand the comprehensive behavior of sedimenting micro-particles in fluids. Here, we use the numerical refocusing feature of digital holographic microscopy (DHM) to investigate the slippage effect on micro-particle sedimentation near a flat wall. DHM provides quantitative phase contrast and three-dimensional (3D) imaging in arbitrary time scales, which suggests it as an elegant approach to investigate various phenomena, including dynamic behavior of colloids. 3D information is obtained by post-processing of the recorded digital holograms. Through analysis of 3D trajectories and velocities of multiple sedimenting micro-particles, we show that proximity to flat walls of higher slip lengths causes faster sedimentation. The effect depends on the ratio of the particle size to (1) the slip length and (2) its distance to the wall. We corroborate our experimental findings by a theoretical model which considers both the proximity and the particle interaction to a wall of different hydrophobicity in the hydrodynamic forces.

In order to generate high quality regular optical vortex array (OVA), we present an experimental method for generating OVA using phase only liquid crystal spatial light modulator (LC-SLM) assisted two gratings. In the scheme, holograms of two grating are displayed on the screen of two LC-SLMs respectively; the diffraction optical fields are captured by a CCD camera. The simulated and experimental results show that the regular OVA can be generated by using double diffraction gratings. The generated OVAs have a constant topological charge of ±1. The method can provide a useful pathway to produce regular OVA for some applications in optical communication, particle trapping and optical metrology.

Crosstalk-free reconstruction of multiple images within a single element can greatly boost the image capacity and information security. We herein demonstrate a viable approach by integrating upconversion and holographic images into a single holographic polymer nanocomposite. The holographic image is reconstructed through photopolymerization-induced phase separation under a 460 nm laser and identifiable under room light, while the upconversion image recognizable under a 980 nm laser is photopatterned via spatially photobleaching of the dye embedded in the upconversion nanoparticle (UCNP) shell under 365 nm light. To this end, the lanthanide-doped UCNP in the core/shell/shell nanostructure of NaYF4:20%Yb3+,0.5%Tm3+@NaYF4@SiO2 is designed, and the dye, fluorescein isothiocyanate (FITC), is fixed in the outermost SiO2 shell via the amine-isothiocyanate reaction and the subsequent sol-gel reaction. Energy transfer from the core of the UCNP to FITC embedded in the shell is critical to boosting the contrast of the upconversion image, which dials the emission color from blue to yellow-green. It is also found that the upconversion image can be brightened by increasing the UCNP content while the holographic image is weakened when the UCNP content is over 15 wt %. This study paves a new way toward advanced anticounterfeiting.

Metasurfaces are composed of periodic sub-wavelength nanostructures and exhibit optical properties that are not found in nature. They have been widely investigated for optical applications such as holograms, wavefront shaping, and structural color printing, however, electron-beam lithography is not suitable to produce large-area metasurfaces because of the high fabrication cost and low productivity. Although alternative optical technologies, such as holographic lithography and plasmonic lithography, can overcome these drawbacks, such methods are still constrained by the optical diffraction limit. To break through this fundamental problem, mechanical nanopatterning processes have been actively studied in many fields, with nanoimprint lithography (NIL) coming to the forefront. Since NIL replicates the nanopattern of the mold regardless of the diffraction limit, NIL can achieve sufficiently high productivity and patterning resolution, giving rise to an explosive development in the fabrication of metasurfaces. In this review, we focus on various NIL technologies for the manufacturing of metasurfaces. First, we briefly describe conventional NIL and then present various NIL methods for the scalable fabrication of metasurfaces. We also discuss recent applications of NIL in the realization of metasurfaces. Finally, we conclude with an outlook on each method and suggest perspectives for future research on the high-throughput fabrication of active metasurfaces. [Image: see text]

Three-dimensional (3D) nanoarchitectures have offered unprecedented material performances in diverse applications like energy storages, catalysts, electronic, mechanical, and photonic devices. These outstanding performances are attributed to unusual material properties at the nanoscale, enormous surface areas, a geometrical uniqueness, and comparable feature sizes with optical wavelengths. For the practical use of the unusual nanoscale properties, there have been developments for macroscale fabrications of the 3D nanoarchitectures with process areas over centimeter scales. Among the many fabrication methods for 3D structures at the nanoscale, proximity-field nanopatterning (PnP) is one of the promising techniques that generates 3D optical holographic images and transforms them into material structures through a lithographic process. Using conformal and transparent phase masks as a key factor, the PnP process has advantages in terms of stability, uniformity, and reproducibility for 3D nanostructures with periods from 300 nm to several micrometers. Other merits of realizing precise 3D features with sub-100 nm and rapid processes are attributed to the interference of coherent light diffracted by phase masks. In this review, to report the overall progress of PnP from 2003, we present a comprehensive understanding of PnP, including its brief history, the fundamental principles, symmetry control of 3D nanoarchitectures, material issues for the phase masks, and the process area expansion to the wafer-scale for the target applications. Finally, technical challenges and prospects are discussed for further development and practical applications of the PnP technique.

Acoustic hologram enable the capability in the acoustic pattern control and drive many applications of ultrasound. However, hologram has not been applied to ultrasound imaging because the medical application of acoustic holograms is limited owing to the sound reflection and scattering at the acoustic holographic surface and its internal attenuation. In this study, we propose an acoustic holographic computing method and present a disc-shaped hologram with a central hole comparing with a conventional hologram using the iterative angular spectrum approach. The results show that the transducer with hole hologram achieves the required focusing effect with the full width at half maximum about $1.5\lambda $ , high sensitivity increased by 92.7%, and a low two-way insertion loss with −15.8 dB compared to conventional hologram. Pulse-echo and ultrasonic imaging are achieved by a transducer with two holograms which shows new applications of acoustic hologram in ultrasound.

The demand for plywood products for the interior and exterior construction has grown significantly over the years. Therefore, detection of defects present in the plywood is of prime importance to maintain good quality of construction. In this study, qualitative and quantitative analyses of defects in plywood using digital holographic interferometric technique are presented. In this process, thermal and mechanical loads are applied to the test sample of plywood to generate interferometric fringes by comparing the normal and stressed states of the test sample. A portable digital holographic camera developed for non-destructive testing applications is employed for detection of cracks, delamination, edge defects, and layer opening in the plywood. The defects in the plywood sample are identified by observing discontinuities in the interferometric fringes. Quantitative analysis of defects is performed by plotting their 2-D and 3-D phase profiles from the digital holographic interferometric results. The obtained results of defects on plywood are validated by a mechanical profiler.

Controlling the crystallographic orientation of 3D photonic crystals is important as it determines the behavior of light propagating through the device. Blue phases self-assemble into unique soft 3D photonic crystals with chiral structures for circular-polarization selectivity, but it has remained a challenge to control its 3D orientation. Here, we show that the orientation of blue phases can be precisely controlled to follow a predefined pattern imprinted on a substrate by exploiting field-induced phase transitions. Obtaining the blue phase through the field-induced chiral nematic phase and tetragonal blue phase X results in a highly oriented blue phase I with the crystallographic [001] direction aligned along the surface anchoring. Our approach is applied to fabricating a Bragg-Berry hologram with omnidirectional circular-polarization selectivity, where the hologram is visible only for one circular-polarization under all incident angles. Such devices are difficult to fabricate using conventional optical materials, thereby demonstrating the potential of self-organizing soft matter for photonics. Controlling the alignment of blue phase liquid crystals is challenging. Here, electric-field induced phase transitions are exploited to control the crystal orientation of blue phase I, and applied to the fabrication of holograms with omnidirectional circular-polarization selectivity.

Metasurfaces composed of subwavelength optical antennas offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Sufficient phase tunability of metasurfaces has significant potential for dynamic beam steering, hologram and flat optics exhibiting tunable focusing. Here, we demonstrate a graphene based metasurface that gives rise to more than 330° smooth and continuous phase modulation at mid-infrared spectrum. The phase modulator model introduces multiple resonances including Split-Ring-resonator (SRR) resonance and inductance-capacitance (LC) resonance, leading to the outstanding sensitivity of the metasurface to tiny change of surrounding electromagnetic environment. Through adjusting the Fermi level of the monolayer graphene beneath the resonators, both scattered amplitude and phase can be efficiently modulated, so that the electrically programmable metasurface enables nearly arbitrary manipulation of scattered wavefront. Electro-optically tunable focusing and beam steering are numerally realized by constructing one dimensional discrete array element. The phased array design achieves an average efficiency up to 22% within 60° steering range. The reflective focusing lens with focal lengths of 10 μm, 15 μm and 20 μm are successfully demonstrated, respectively. The proposed metasurface has promising potential in optoelectronic applications such as imaging, sensing and focusing.

The possibility of volumetric phase recording based on photo-oxidation of the side anthracene groups of a new polymer with a glass transition temperature of ~338 K by oxygen that enters the layer across the boundary with the atmospheric medium, was established experimentally. Volumetric holographic gratings with a maximum diffraction efficiency of 2.5–9.5% were recorded with the radiation from a He–Ne laser (λ = 633 nm) in layers 5–20-μm thick. It was shown that in layers thicker than 10 μm the diffraction efficiency is limited by saturation of growth in the modulation depth of the optical path difference. This effect is due to increase in the radius of the photorefraction sphere around the photosensitizer molecule with the increased photoconversion of the anthracene groups, which lowers the resolution of the holographic grating and its effective thickness.

Holographic sensors are two-dimensional (2D) photonic crystals that diffract narrow-band light in the visible spectrum to quantify analytes in aqueous solutions. Here, a holographic fabrication setup was developed to produce holographic sensors through a doubly polymerization system of a poly-2-hydroxyethyl methacrylate hydrogel film using a pulsed Nd:YAG laser (λ = 355 nm, 5 ns, 100 mJ). Wavelength shifts of holographic Bragg peak in response to alcohol species (0-100 vol %) were characterized. Diffraction spectra showed that the holographic sensors could be used for short-chain alcohols at concentrations up to 60 vol %. The reversibility of the sensor was demonstrated, exhibiting a response time of 7.5 min for signal saturation. After 30 cycles, the Bragg peak and color remained the same in both 20 and 60 vol %. The fabrication parameters were simulated in MATLAB using a 2D finite-difference time-domain algorithm to model the interference pattern and energy flux profile of laser beam recording in the hydrogel medium. This work demonstrates a particle-free holographic sensor that offers continuous, reversible, and rapid colorimetric readouts for the real-time quantification of alcohols.

The aim of this study was to quantify vibrations and their influence on visual acuity. The study consisted of two parts, laboratory and clinical. Time-averaged holographic interferometry (TAHI) method was used in laboratory for measuring the amplitude of tooth vibrations induced by dental handpiece. The amplitudes of tooth vibrations were measured for the three diameters and three speeds. The larger diameter coupled with increasing speed resulted in greater vibration amplitudes, whereby a maximum amplitude of less than one micrometer was detected. For quantifying the natural visual acuity for the corresponding tooth vibrations, we have used the clinical condition approach with miniaturized Snellen optotype as an assessing tool. Central visual acuity did not display variance in visual acuity at rest or under load. Results indicate that the vibrations induced during cavity preparation are not sufficient to negatively affect visual acuity of dentists.

Controlling thermal emission plays a vital role in various applications. Existing control of thermal emissions have been limited to simple functions such as directional and spectral selectivity. Co...

We propose a new approach for dynamic holography at optical frequencies utilizing a cavity incorporating an active VO2 layer. By introducing a Bragg reflector at the bottom side of the active cavity, it is possible to obtain a 180° phase shift between the reflected waves in the cold and hot states of the VO2, while maintaining the reflectivity constant at ∼60%. Utilizing this property, we propose and analyze a reconfigurable metasurface which can realize tunable binary holography at optical frequencies. We study the potential performances of such reconfigurable hologram and their sensitivity to variations in the wavelength, polarization and illumination angle. We also show that when tuned to the proper temperature this device can serve as broad-angle perfect absorber.

To increase the angular bandwidth of volume holographic grating, we fabricate holographic gratings based on grating multiplexing technique by using thin films of photopolymers and polymer dispersed liquid crystals. Experimental results confirm that the liquid crystal materials increase the refractive index modulation of the grating, enabling high diffraction efficiency with wide angular response compared to pure polymer materials. We observe that the fabricated holographic grating has near 80% of diffraction efficiency and about 18° of angular bandwidth, which can be further improved by modifying the liquid crystal/polymer mixtures and the grating multiplexing technique. The grating can be used to fabricate holographic waveguide structures for emerging applications in the near-eye display systems.

In this paper, we have studied the deformation of cylindrical nanostructured silica aerogels prepared with methyltrimithoxysilane (MTMS) precursor. Two beam phase-shifting digital holographic interferometry (PSDHI) is applied along with a two-beam illumination technique to study in-plane displacements. To obtain the aerogels with different densities, the MeOH/MTMS molar ratio was systematically increased from the value 20 to 26. The cylindrical aerogels are loaded with various loads from the top surface. Phase shifted holograms of silica aerogels with varying densities, with and without deformation, are recorded with two beam illumination by CCD camera. Fresnel Diffraction integral is used to reconstruct the complex amplitude of aerogel samples. For in-plane displacements, phase distribution in deformed aerogels is determined by measuring the change in the two-phase distributions. The patterns corresponding to the phase distribution of aerogels for different loads and densities are recorded. It has been observed that the deformation of silica aerogels reduces by the value 0.02058 cm to 0.0017 cm, with an increase in bulk density 0.01742 gm/cc to 0.1952 gm/cc. The elastic behavior of aerogels has been explained under various loads by considering the phase distribution patterns and condensation reaction.

The behavior of aluminum particles during Al/AP propellant combustion is studied by 25 kHz high-speed digital off-axis holography and high-speed microscopic imaging. The advantage of off-axis holography is that the effects of the enveloping flame are suppressed, thereby, achieving better burning particle imaging. Three-dimensional dynamics of the aluminum particles from a series of time-resolved holograms are given in order to study the motion behaviors of particles during combustion. Typical processes, e.g., formation and change of the condensed phase products, micro-explosion behavior, and diameter ratio of enveloping flame and Al particle, are analyzed. This work provides a new 3D approach, that is, high-speed digital off-axis holographic imaging, for studying solid propellant combustion.

Although the manufacturing processes of contact lenses are well established, the use of additive manufacturing for their fabrication opens many new possibilities to explore. The current study demonstrates the fabrication of personalized smart contract lenses utilizing additive manufacturing. The study includes 3-dimensional (3D) modeling of contact lenses with the assistance of a computer aided designing tool based on standard commercial contact lens dimension, followed by the selection of the suitable materials and 3D printing of contact lenses. The 3D printing parameters were optimized to achieve the desired lens geometries, and a post processing treatment was performed to achieve a smooth surface finish. The study also presents functionalized contact lenses with built-in sensing abilities by utilizing microchannels at the contact lens edges. Tinted contact lenses were printed and nanopatterns were textured onto the contact lens surfaces through holographic laser ablation. 3D printed contact lenses have advantages over conventional contact lenses, offering customized ophthalmic devices and the capability to integrate with optical sensors for diagnostics.

Holography can produce the most real three-dimensional (3D) image, and is considered as the ultimate 3D display technology. However, compared with other display technologies, it has not been practically available in video display so far due to low refresh rate. To realize dynamic holographic display, photosensitive material doped liquid crystal (LC) has been discovered and deeply investigated because of superior photorefractive and photoelectric properties. In this work, we present a dynamic holographic display using LC film doped with perovskite (CsPbBr3) nanocrystal (NC) as the photorefractive material. The dependence of diffraction efficiency and response time on doping concentration, recording beam power and applied voltage are investigated. A maximum diffraction efficiency of 18% has been achieved under a low electric field intensity of 0.45 V/μm and the shortest build-up time of grating is 5.5 ms. The system can realize a video display with 60 Hz refresh rate in red, green and blue colors, which demonstrates the feasibility of applying perovskite NC doped LC film in dynamic holographic display.

An analytical model of the diffraction of quasi-monochromatic light beams on spatially inhomogeneous multilayer diffraction structures formed in a photopolymer material by holographic means is presented. This model allows for inhomogeneities in the amplitude profile of the first harmonic of the refractive index of each layer of the multilayer structure.