Transmission Holograms Research Articles

Comparing thin and volume regimes of analog holograms for wavefront sensing.

Two analog holographic wavefront sensors, for measurement of defocus, have been fabricated as both thin and volume phase transmission holograms in a self-developing photopolymer. This represents the first reported direct comparison of hologram regimes when designed for wavefront sensing. An analysis of the effect of crosstalk in the presence of one other aberration mode (astigmatism X (0/90°), coma X (horizontal), and primary spherical aberration) was carried out with each version of the sensor. The performance of thin and volume analog holographic wavefront sensors was characterized under emulated conditions associated with moderate atmospheric turbulence.

Multiplexed digital volume reflection holograms generated from digital transmission holograms.

Interference from co-propagation of the object and reference beams can be digitally recorded for a digital transmission hologram (DTH). Volume holograms, as in display holography, which have been traditionally recorded in bulk photopolymer or photorefractive materials using a counter-propagating object and writing beams, are read out using multispectral light and offer the advantage of excellent wavelength selectivity. In this work, the reconstruction from a single digital volume reflection hologram (DVRH) and wavelength multiplexed DVRHs derived from respective single and multi-wavelength DTHs is investigated, using coupled wave theory and an angular spectral approach. The dependence of the diffraction efficiency on volume grating thickness, wavelength, and incident angle of the reading beam is studied.

Compact near-eye display with a wide FOV and a wide eye box using 24 multiple-exposure holograms.

A compact near-eye display with a 60° horizontal field of view, wide eye box of 5 mm, and high resolution of 720 p is proposed and developed by combining a transmission hologram that duplicates the beam of a scanning display and a reflection hologram that reflects duplicated beams toward the user's eye. The feasibility of the proposed near-eye display is demonstrated by examining the specifications and exposure of 24 multiple holograms. A compact NED that can display images with a horizontal FOV of 60° and that has a 6.2 mm × 4.8 mm eye box and 720 pixels vertical resolution is achieved.

Holographic point source for digital lensless holographic microscopy.

A holographic point source (HPS) developed for digital lensless holographic microscopy (HPS-DLHM) is presented. The HPS is an off-axis phase transmission hologram of an experimental micrometer pinhole recorded on a photopolymer holographic film. An amplitude division interferometer, adjusted to operate at maximum diffraction efficiency, has been employed to record the hologram. The results of HPS-DLHM have been contrasted with the results obtained via conventional DLHM, and the two techniques were found to give similar measurements. Compared with conventional pinhole-based DLHM illumination, our cost-effective proposal provides increased mechanical stability, the possibility of wider spherical illumination cones, and shorter reconstruction distances. These superior features pave the way to applying this quantitative phase imaging (QPI) technique in biomedical and telemedicine applications. The imaging capabilities of our HPS-DLHM proposal have been tested by using an intricate sample of a honeybee leg, a low-absorption sample of epithelial cheek cells, a 1951 USAF test target, and smeared human erythrocytes.

Processing of Holographic Hydrogels in Liquid Media: A Study by High-Performance Liquid Chromatography and Diffraction Efficiency.

The storage of time-stable holographic gratings in hydrogel matrices when the material is immersed in aqueous media is a real challenge at present. The optimization of the storage stages of the holograms must be properly investigated to identify the most suitable development processes. For this reason, this work is focused on the study of the optimization of the washing stages of the hydrogels based on acrylamide and N,N’-methylenebis(acrylamide) once unslanted transmission holograms have been stored. High-performance liquid chromatography and UV-visible measurements have been employed in our system to analyze the composition of the washing solutions. PBST and DMSO:H2O are used as solvents in the washing stages. The diffraction efficiencies are measured during the washing stages and after the storing of the holograms during several days in PBST. Maximum diffraction efficiencies of 38 and 27.6% are reached when PBST and DMSO:H2O are employed, respectively, for the washing process. Holograms show temporal stability after being stored immersed in PBST at 4 °C for 4 days.

Stakeholders' Perceptions regarding the use of Hologram for Educational Purposes in District Toba Tek Singh, Pakistan

Hologram is essential in education because it is more helpful for students to clear their concepts through moving objects and engaging many students. Different hologram types are used in various educational institutes such as reflection holograms, transmission holograms, and pyramid holograms. It is an exciting and widely discussed tool in the world. ICTs are frequently used, such as computers, laptops, projectors, smart boards, and other audiovisual aids. The study's purpose was to attain stakeholders' perceptions regarding the use of holograms for educational purposes in District Toba Tek Singh, Punjab, Pakistan. The total sample size of 116 respondents were selected from the population by using a simple random sampling technique. The results indicated that most of the respondents were agreed that the strengths of hologram technology could be meaningful in the teaching-learning process. It is also concluded that students fear new technology will be less and more time-saving due to hologram technology use in the teaching-learning process. It also discovered that lack of leadership's quality was a significant barrier to adopting hologram technology in the education system.

Study of Full-Color Multiplexed Transmission Holograms of Diffusing Objects Recorded in Photopolymer Bayfol HX

A wavelength multiplexing procedure for color transmission volume holograms of diffusing objects recorded in Bayfol® HX200 photopolymer is proposed. For the recording, three lasers of 442 nm, 532 nm and 633 nm, and a Spectralon® diffusing object were used for monochromatic and polychromatic calibration. Monochromatic calibration shows that the maximum index modulation obtained for each wavelength was not enough to give 100% efficiency, although the efficiency values achieved in the case of monochromatic recordings with diffusing objects were high, at around 90% for 633 nm and 532 nm recordings, and 60% for 442 nm. The efficiency values obtained for multiplexed holograms were 19.1% for the 442 nm hologram, 25.9% for the 532 nm hologram and 15.2% for the 633 nm.

Thick PQ:PMMA transmission holograms for free-space optical communication via wavelength-division multiplexing.

Phenantrenequinone doped poly(methyl-methacrylate) (PQ:PMMA) is a holographic substrate that can be used for angle or wavelength multiplexed Bragg gratings. However, efficient writings can be done only using a high-power, long-coherence volume laser over a limited wavelength range. This constraint makes it difficult to write gratings that would diffract several different read wavelengths into a single direction. We describe the rules for writing such gratings, taking into account the differences in the mean index seen by the write and read wavelengths. We further demonstrate the use of such a transmission hologram for wavelength-division multiplexing in a free-space optical communication system.

A transmission hologram for slitless spectrophotometry on a convergent telescope beam. 1. Focus and resolution

ABSTRACT We report in this paper the test of a plane holographic optical element to be used as an aberration-corrected grating for a slitless spectrograph, inserted in a convergent telescope beam. Our long-term objective is the optimization of a specific hologram to switch the auxiliary telescope imager of the Vera Rubin Observatory into an accurate slitless spectrograph, dedicated to the atmospheric transmission measurement. We present and discuss here the promising results of tests performed with prototype holograms at the CTIO $0.9\,$m telescope during a run of 17 nights in 2017 May–June. After their on-sky geometrical characterization, the performances of the holograms as aberration-balanced dispersive optical elements have been established by analysing spectra obtained from spectrophotometric standard stars and narrow-band emitter planetary nebulae. Thanks to their additional optical function, our holographic disperser prototypes allow us to produce significantly better focused spectra within the full visible wavelength domain $[370,1050]\,$nm than a regular grating, which suffers from strong defocusing and aberrations when used in similar conditions. We show that the resolution of our slitless on-axis spectrograph equipped with the hologram approaches its theoretical performance. While estimating the benefits of a hologram for the spectrum resolution, the roadmap to produce a competitive holographic element for the Vera Rubin Observatory auxiliary telescope has been established.

Effect of Glycerol on an N-Vinylpyrrolidone-Based Photopolymer for Transmission Holography.

N-vinylpyrrolidone (NVP) has a large molecular structure, so it is difficult to diffuse during holographic recording, especially at low spatial frequencies. We used glycerol to promote the diffusion of NVP, and successfully improved the holographic performance of the photopolymer at low spatial frequencies. As the concentration of glycerol increases, the holographic performance first increases and then remains stable. The optimal concentration of glycerol is 0.21 mol/L. At this concentration, the maximum diffraction efficiency of the photopolymer is 84%, the refractive index modulation is 1.95 × 10−3, and the photosensitive sensitivity is 7.91 × 10−4 cm2/mJ. Compared with the control group, the maximum diffraction efficiency, maximum refractive index modulation and photosensitivity at low spatial frequencies (800 lp/mm) have increased by 11.19 times, 4.69 times and 1.71 times, respectively. Using the optimized photopolymer for transmission holographic recording and reproduction, we have obtained a clear and bright transmission hologram. The photopolymer modified with glycerol is expected to be applied to the fields of holography, diffractive optics, and so on.

Closer look at transmissive polarization volume holograms: geometry, physics, and experimental validation.

In this work, we took a closer look at transmissive polarization volume holograms (T-PVH) to provide clarifications on their geometry, physics, and optical responses by finite-difference time-domain (FDTD) simulation and experimental validation. First, we introduced the four possible geometries of T-PVH and simulated their optical responses in terms of diffraction efficiency, polarization selectivity, and polarization output. It is shown that the configuration we called "Slanted T-PVH (B-θ/D-θ+90)," where the director is perpendicular to the Bragg planes, has the advantageous property of maintaining circular output polarization states. For this configuration, a detailed simulation of spectral, angular, and polarization responses was completed. Finally, we validated the FDTD simulation results of the Slanted T-PVH (B-θ/D-θ+90) structures with experiments.

Influence of Photoelastic and Piezoelectric Effects on the Energetic Characteristics of Transmission and Reflection Holograms in a Photorefractive Crystal

The surface of the normal component of the inverse tensor of the dielectric permittivity of a cubic photorefractive piezoelectric Bi12SiO20 crystal was constructed. A volume phase holographic grating with a wave vector along the $$ \left[1\overline{1}1\right] $$ crystallographic axis was recorded in this crystal. It is established that the combined action of the photoelastic and piezoelectric effects leads to an increasing normal component of the inverse tensor of the dielectric permittivity along the $$ \left[1\overline{1}1\right] $$ direction and a decreasing normal component of the inverse tensor of the dielectric permittivity in the perpendicular direction. It is revealed that the anisotropy of the contribution of the photoelastic and piezoelectric effects causes an increase in the output energetic characteristics (optimized in the azimuth of polarization of light waves) for the transmission hologram and their decrease for the reflection hologram.

Analysis of the Imaging Characteristics of Holographic Waveguides Recorded in Photopolymers.

In this work, we study the imaging characteristics of an optical see-through display based on a holographic waveguide. To fabricate this device, two transmission holograms are recorded on a photopolymer material attached to a glass substrate. The role of the holograms is to couple the incident light between air and the glass substrate, accomplishing total internal reflection. The role of noise reflection gratings and shrinkage on the imaging characteristics of the device will be also explored. The holograms (slanted transmission gratings with a spatial frequency of 1690 lines/mm) were recorded on a polyvinyl alcohol acrylamide holographic polymer dispersed liquid crystal (HPDLC) material. We will show that sufficient refractive index modulation is achieved in the material, in order to obtain high diffraction efficiencies. We will demonstrate that the final device acts as an image formation system.

Exact design of complex amplitude holograms for producing arbitrary scalar fields.

Typical methods to holographically encode arbitrary wavefronts assume the hologram medium only applies either phase shifts or amplitude attenuation to the wavefront. In many cases, phase cannot be introduced to the wavefront without also affecting the amplitude. Here we show how to encode an arbitrary wavefront into an off-axis transmission hologram that returns the exact desired arbitrary wavefunction in a diffracted beam for phase-only, amplitude-only, or mixed phase and amplitude holograms with any periodic groove profile. We apply this to design thin holograms for electrons in a TEM, but our results are generally applicable to light and X-ray optics. We employ a phase reconstruction from a series of focal plane images to qualitatively show the accuracy of this method to impart the expected amplitude and phase to a specific diffraction order.

Influence of Inverse Piezoelectric Effect, Photoelasticity, and Optical Activity on the Diffraction Efficiency of Transmissing Holograms in Photorefractive Crystal Bi12SiO20

The results of a theoretical study of the dependence of the diffraction efficiency of a transmission hologram formed in a sample of a Bi12SiO20 photorefractive crystal on the orientation angle, specific rotation of the crystal, and its thickness are presented. The theoretical model takes into account linear electrooptical, inverse piezoelectric and photoelastic effects. It is shown that with a change in the sign of the specific rotation of the crystal, there can be a shift of the maximums of diffraction efficiency relative to the orientation angle.

Diffraction Efficiency of Mixed Transmission Holograms in a Photorefractive Optically Active Bi12TiO20 Piezoelectric Crystal of Arbitrary Cut

The process of reading mixed transmission holograms formed in a photorefractive Bi12TiO20 piezoelectric crystal (sillenite family) of arbitrary cut has been theoretically optimized. The optimal crystal cuts, which provide the highest diffraction efficiency of holograms, are determined. The results of the theoretical analysis are based on the previously obtained experimental data; they are in agreement with the crystal point symmetry group and may serve as the basis for increasing the efficiency of dynamic holography devices with Bi12TiO20 crystals.

3D hologram in futuristic classroom: A review

Holography is a photographic method that records the light dispersed from a body and then produces a realistic image identified as three-dimensional Holograms. The hologram reflects and transmits using a point source of incandescent light or two-channel transmission hologram. In the world of education, 3D holograms can be integrated into mixed reality classrooms to ease the teaching and learning process. The significance of this application is to enable the 21st Century learners to experience the realistic content via 3D Holograms, thereby improving their learning curves. This paper highlights the fundamental concepts of hologram and discusses the diversified implementations of hologram as a mixed reality simulator in the futuristic classrooms. Recent technological advancements in the field of education and evidence from successful implementation of the mixed reality approach in educational research has also been debated. However, the application of Holograms in education is still confined within boundaries.

Spatial Frequency Response of Epoxy-Based Volume Holographic Recording Material.

Holographic volume phase gratings are recorded in an epoxy-based, free-surface, volume holographic recording material. Light-induced gratings are formed by photo-triggered mass migration caused by component diffusion. The material resolution enables a wide range of pattern spacings, to record both transmission and reflection holograms with many different spatial frequencies. An optimum spatial frequency response is found between the low spatial frequency roll-off and the high spatial frequency cut-off. The influence of the energy density of exposure on the spatial frequency response is investigated. Secondary volume holographic gratings (parasitic gratings) are observed in the high frequency range. The possibility of distinguishing the regular grating from the secondary grating is discussed in the form of probe wavelength detuning.

Self-processing photopolymer materials for versatile design and fabrication of holographic sensors and interactive holograms

The aim of this paper is to discuss the benefits as well as the limitations of utilizing photopolymer materials in the design of holograms that are responsive to changes in their environment, such as changes in the concentration of a specific substance, temperature, and pressure. Three different case studies are presented, including both surface and volume phase holograms, in order to demonstrate the flexibility in the approach of utilizing holographic photopolymers for the design of sensors and interactive optical devices. First, a functionalized surface relief hologram is demonstrated to operate as an optical sensor for the detection of metal ions in water. The sensitivity and selectivity of the sensor are investigated. The second example demonstrates a volume transmission hologram recorded in a temperature-sensitive photopolymer and the memory effects of its exposure to elevated temperature. Finally, a pressure-sensitive reflection hologram that changes color under application of pressure is characterized, and its potential application in document authentication is described.

Design and fabrication of cascaded dichromate gelatin holographic filters for spectrum-splitting PV systems

The technique of designing, optimizing, and fabricating broadband volume transmission holograms using dichromate gelatin (DCG) is summarized for solar spectrum-splitting applications. The spectrum-splitting photovoltaic (PV) system uses a series of single-bandgap PV cells that have different spectral conversion efficiency properties to more fully utilize the solar spectrum. In such a system, one or more high-performance optical filters are usually required to split the solar spectrum and efficiently send them to the corresponding PV cells. An ideal spectral filter should have a rectangular shape with sharp transition wavelengths. A methodology of designing and modeling a transmission DCG hologram using coupled wave analysis for different PV bandgap combinations is described. To achieve a broad diffraction bandwidth and sharp cutoff wavelength, a cascaded structure of multiple thick holograms is described. A search algorithm is then developed to optimize both single- and two-layer cascaded holographic spectrum-splitting elements for the best bandgap combinations of two- and three-junction spectrum-splitting photovoltaic (SSPV) systems illuminated under the AM1.5 solar spectrum. The power conversion efficiencies of the optimized systems are found to be 42.56% and 48.41%, respectively, using the detailed balance method, and show an improvement compared with a tandem multijunction system. A fabrication method for cascaded DCG holographic filters is also described and used to prototype the optimized filter for the three-junction SSPV system.