Volume Phase Holograms Research Articles

Preparation of Panchromatic Silver Halide Emulsion to Fabricate High Efficiency Multiplexed Volume Phase Holograms for Solar Concentration Application

Volume Phase Gratings (VPG) are often recorded using holographic emulsions such as photopolymer, Dichromated Gelatin (DCG), and silver halide. We employed silver halide emulsion to record the VPG in monochromatic red wavelength for solar concentration purposes. According to the Braggs condition, the recorded VPG's diffraction efficiency reaches its peak at the recorded angle and wavelength. For solar applications, we needed high diffraction efficiency over a wide angle and wavelength range. So, we captured multiplexed single VPG in our own panchromatic silver halide emulsion. The procedure of making panchromatic silver halide emulsion is described in depth. This technique is unique in that it achieves peak diffraction efficiency at broad wavelength and wide angle in a single multiplexed VPG. The panchromatic multiplexed VPG produced a high diffraction efficiency in wide-angle response with overall visible wavelengths. This study describes the high diffraction efficiency multiplexed VPG in its own manufactured panchromatic silver halide emulsion for solar concentrating applications.

Storage Optimization of Transmission Holographic Gratings in Photohydrogels.

The development and optimization of holographic materials represent a great challenge today. These materials must be synthesized according to the characteristics that are desirable in photonic devices whose application is the object of investigation. In certain holographic sensors and biosensors, it is essential that the recording material be stable in liquid media. Furthermore, the holographic gratings stored in them must have temporal and structural stability, so that they can act as transducers of the analytical signal. Therefore, it is essential to optimize its storage in terms of the chemical composition of the material and the optical parameters of recording. This work focuses on the study of the storage optimization of unslanted transmission volume phase holograms in photohydrogels based on acrylamide and N,N'-methylenebis(acrylamide). Hydrogel matrices, also composed of acrylamide and N,N'-methylenebis(acrylamide), with different degrees of cross-linking were used and analyzed by scanning electron microscopy and UV-visible spectroscopy. The best results in terms of diffraction efficiency were reached for hydrogel matrices with an acrylamide/N,N'-methylenebis(acrylamide) molar ratio between 19.9 and 26. This relationship was also optimized in the incubator solution used to incorporate the components necessary for the formation of the holograms in the hydrogel matrices. The maximum diffraction efficiency, about 35%, was achieved when using an incubation solution with an acrylamide/N,N'-methylenebis(acrylamide) molar ratio of 4.35. The influence of the physical thickness of the hydrogel layers, the intensity, and the exposure time on the diffraction efficiency was also investigated and optimized. In addition, the behavior of the hologram was analyzed after a washing stage with PBST. A simple model that considered the effects of bending and attenuation of holographic gratings was proposed and used to obtain the optical parameters of the holograms.

Design of Holographic Condenser Lens for Visible Light Lithography

Photolithography with visible light at λ = 405 nm utilizing the concept of nonlinear saturable absorption effect where the size of the spot is diminished to the nanometer scale as proposed by several researchers is an alluring proposition for cost-effective projection lithography. Costly conventional condenser lenses can be replaced by monochromatic aberration-free and cost-effective volume phase holographic lenses for visible light photolithography with enhanced resolution utilizing the concept of off-axis illumination. However, the diffraction efficiency of holographic lenses depends on the wavelength of illuminating light and the angle of illumination. Angular and spectral characteristics of volume phase holograms can be controlled by optimizing processing parameters. The results on the theoretical optimization of three important processing parameters, namely fringe spacing ( ∧ ), thickness of the film ( d ), and refractive index modulation ( Δ n ) in the light of coupled wave theory for recording holographic lenses of high diffraction efficiency at λ = 405 nm are presented. It is pointed out that a properly designed single holographic lens can be used for off-axis illumination of a photomask with a parallel beam of light, whereas a system of two identical holographic lenses cemented together has to be used to realize a condenser lens similar to a converging lens.

Analog holographic wavefront sensor for defocus and spherical aberration measurement recorded in a photopolymer.

An analog holographic wavefront sensor (AHWFS), for measurement of low and high order (defocus and spherical aberration) aberration modes has been developed as volume phase holograms in a photopolymer recording medium. This is the first time that high order aberrations such as spherical aberration can be sensed using a volume hologram in a photosensitive medium. Both defocus and spherical aberration were recorded in a multi-mode version of this AHWFS. Refractive elements were used to generate a maximum and minimum phase delay of each aberration which were multiplexed as a set of volume phase holograms in an acrylamide based-photopolymer layer. The single-mode sensors showed a high degree of accuracy in determining various magnitudes of defocus and spherical aberration generated refractively. The multi-mode sensor also exhibited promising measurement characteristics and similar trends to the single-mode sensors were observed. The method of quantifying defocus was improved upon and a brief study into material shrinkage and sensor linearity is presented.

Intuitive understanding of the connection between Pancharatnam-Berry optical beam deflectors and polarization volume holograms.

An approximate beam propagation method is proposed as an intuitive simulation of the optics of Pancharatnam-Berry phase and polarization volume hologram devices. Using this method, the connection between and polarization properties of these two types of devices are made clear.

Modelling of a composite waveguide holographic display

Optical designs of waveguide-type augmented reality displays are investigated. Displays based on volume phase holograms are notable for their small size, large exit pupil and high transmittance both in the projected image channel and in the direct vision channel. However, with an increase of the aperture, field of view and working spectral range, the spread of the values of the beam angle of incidence and the wavelength increases when solving the diffraction problem at different points on the hologram surface which imposes restrictions on spatial resolution and diffraction efficiency. To overcome this phenomenon, it is proposed to use a composite hologram which represents a volume phase grating divided into zones with independently varying parameters of the fringes tilt, their shape, the holographic layer thickness and the refraction index modulation depth. We propose an algorithm that allows ray tracing through a hologram recorded by two coherent point sources using an auxiliary aspherical mirror. The initial ray tracing in the hologram recording scheme is performed using the error function minimization by the orthogonal descent and golden section methods. Based on the results obtained, the directional vectors of the diffracted beam are calculated using the Welford equation. Using the tracing results, the hologram diffraction efficiency is computed with the Kogelnik’s coupled wave theory. The proposed algorithms are implemented in the Zemax Optics Studio software. The application of the proposed composite hologram element and the tools for operation modeling are shown on an example of display operating in the range of 510–530 nm with the field of view of 7°36ʹ × 5°48ʹ and the exit pupil diameter of 8 mm. It is shown that the proposed solutions make it possible to increase the diffraction efficiency by 3.45 times. At the same time, the spatial resolution increases by 12.7 % varying across the field of view in the range of 0ʹ44ʺ–1ʹ6ʺ. The use of composite holograms allows one to create displays with higher spatial resolution and brightness of the projected image as well as uniformity of the characteristics across the field of view.

Water Resistant Cellulose Acetate Based Photopolymer for Recording of Volume Phase Holograms

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from the environment is required. One approach to solving this challenge is to select substrate such as cellulose acetate, which is water resistant. This work reports the development of a cellulose-based photopolymer with sensitivity of 3.5 cm2/mJ and refractive index modulation of 2.5 × 10−3 achieved in the transmission mode of recording. The suitability for holographic recording was demonstrated by recording gratings with the spatial frequency of 800 linepairs/mm. The intensity dependence of the diffraction efficiency of gratings recorded in 70 μm thick layers was studied and it was observed that the optimum recording intensity was 10 mW/cm2. The robustness of the structures was studied after immersing the layer in water for one hour. It was observed that the diffraction efficiency and the surface characteristics measured before and after exposure to water remain unchanged. Finally, the surface hardness was characterized and was shown to be comparable to that of glass and significantly higher than the one of PVA-based acrylamide photopolymer.

Cover Image, Volume 59, Issue 13

Journal of Polymer ScienceVolume 59, Issue 13 p. i-i FRONT COVERFree Access Cover Image, Volume 59, Issue 13 First published: 01 July 2021 https://doi.org/10.1002/pol.20210470AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract The cover image represents free-radical ring-opening polymerization of cyclic allylic sulfide (CAS) monomers used by Paola Galli and colleagues for their article on page 1398 on highly efficient volume phase holograms. This type of monomers allows the transfer of the holographic pattern with high fidelity. Reaching high efficiencies is obtained through the combination of the CAS monomer with thiol cross-linkers and applying a thermal post process to the samples. Image credits: Paola Galli, Chiara Righi and Francesca Salimbene. (DOI: 10.1002/pol.20210192). Volume59, Issue13July 1, 2021Pages i-i RelatedInformation

Design procedure for a holographic display considering the diffraction efficiency of a volume phase hologram

A procedure for the design of optical schemes of holographic displays is developed. The procedure implies the simultaneous optimization of the image quality factors and the root-mean-square values of the hologram diffraction efficiency at the control points. The procedure is implemented at the level of specific software tools and utilized for the design of an example scheme of a waveguide holographic display. The display operates within the 480–620 nm spectral range and has a 10° angular field of view and an exit pupil diameter of 10 mm. The input of radiation into the waveguide plate and the radiation output are achieved using diffractive elements operating in the transmitted light. The output element in this case is a volume phase hologram recorded by two point sources. The calculation results show that the implementation of the proposed design makes it possible to reduce the radius of the circle of confusion in terms of the angular measure by 0.28′−0.97′. The diffraction efficiency of the output hologram in this case is closer to the target value by 2.5% to 19%.

Formfactor of a hologram on a chalcogenide glassy semiconductor and azopolymer

In this work, the formfactor influence on the diffraction efficiency of 2D and 3D phase holograms was analyzed. Experimental results showed that holograms recorded in a chalcogenide glassy semiconductor and an azopolymer have limitations on maximum achievable diffraction efficiency. The coefficient of optimal exposure increase that is necessary to achieve maximum achievable diffraction efficiency was obtained. Due to the difference between the values of the formfactor in the case of the Raman-Nath diffraction and of that in the case of the Bragg diffraction for diffraction on thin (2D) holograms, the value of the formfactor turned out to be larger than that for diffraction on volume (3D) phase holograms.

Method of calculation of a hologram display taking into account the diffraction efficiency of a volume-phase hologram

Method of calculation of a hologram display taking into account the diffraction efficiency of a volume-phase hologram

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.

Index and gain gratings in Nd-YVO4 - Applications to speckle vibrometry and photoacoustic detection

We perform wave mixing and dynamic holography by exploiting gain saturation in diode pumped laser media like Nd-YVO4. Such crystals offer the possibility of performing adaptive gain interferometers with a sub ms response time, typically between 100- 200μs. This temporal response is of great interest for applications such as speckle interferometry and acousto-optic detection for tissue imaging in biophotonics. In this work we operate in new conditions of high sensitivity with a linear response due to a refractive index contribution in the gain media. It originates from the wavelength mismatch of about 0.1 nm between the incident Nd-YAG probe laser and laser transition in diode pumped Nd-YVO4 amplifier. This permits the recording of two types of volume holograms respectively a gain and a phase volume holograms. It is the index grating which provides a linear response to incident low phase modulation at frequencies higher than 10 kHz. Experimental results confirm this behavior for adaptive interferometry and speckle vibrometry. In addition, the fast response makes the two wave mixing interaction in Nd-YVO4 very interesting for the optical detection of large bandwith photoacoustic waves excited by a pulsed ns Q-Switch laser at 532 nm. Temporal photoacoustic signals and images of small objects behind a scattering media will be shown.

Optical nonlinearities of small polarons in lithium niobate

An overview of optical nonlinearities of small bound polarons is given, which can occur in the congruently melting composition of LiNbO3. Such polarons decisively influence the linear and nonlinear optical performance of this material that is important for the field of optics and photonics. On the basis of an elementary phenomenological approach, the localization of carriers in a periodic lattice with intrinsic defects is introduced. It is applied to describe the binding energies of four electron and hole small polarons in LiNbO3: small free NbNb4+ polarons, small bound NbLi4+ polarons, small bound NbLi4+:NbNb4+ bipolarons, and small bound O− hole polarons. For the understanding of their linear interaction with light, an optically induced transfer between nearest-neighboring polaronic sites is assumed. It reveals spectrally well separated optical absorption features in the visible and near-infrared spectral range, their small polaron peak energies and lineshapes. Nonlinear interaction of light is assigned to the optical formation of short-lived small polarons as a result of carrier excitation by means of band-to-band transitions. It is accompanied by the appearance of a transient absorption being spectrally constituted by the individual fingerprints of the small polarons involved. The relaxation dynamics of the transients is thermally activated and characterized phenomenologically by a stretched exponential behavior, according to incoherent 3D small polaron hopping between regular and defect sites of the crystal lattice. It is shown that the analysis of the dynamics is a useful tool for revealing the recombination processes between small polarons of different charge. Nonlinear interaction of small polarons with light furthermore results in changes of the index of refraction. Besides its causal relation to the transients via Kramers-Kronig relation, pronounced index changes may occur due to optically generated electric fields modulating the index of refraction via the linear electro-optic effect, also. Based on a microscopic picture and by considering the local structural environment of bound polarons, the appearance of photovoltaic currents is explained straightforwardly as a result of the optically induced carrier transfer. Both transient absorption and index changes are spatially confined to the intensity profile of the interacting light allowing for the recording of efficient mixed absorption and phase volume holograms. By means of holographic spectroscopy, these small-polaron based optical nonlinearities are verified either without or with the action of the linear electro-optic effect; their prominent features are highlighted by appropriate experimental studies wherin the ultrafast response on the picosecond time scale is the most recognized one. Based on these findings, the consequences for applications of LiNbO3 in the field of nonlinear optics and photonics are presented. Besides visionary examples like real-time, 3D holographic displays, the impact of optical nonlinearities of small polarons for present applications are discussed with frequency conversion and respective limiting effects, such as green-induced infrared absorption and optical damage, as important example.

Formation Dynamics of Transmission Holograms in Lithium Niobate Crystals Doped by Copper Through High-Temperature Diffusion

The results of experimental realization of the technology of diffusion doping of X-cut congruent lithium niobate crystals by copper and the results of studying their photorefractive and photovoltaic properties are presented. The latter was done by using the Bragg diffraction of the reading beam with a wavelength of 655 nm on the dynamic transmission volume–phase holograms recorded by laser beams having a wavelength of 532 nm. It is shown that by their photogalvanic properties the created samples, which are 1.8 mm thick, are similar to the single crystals grown by the conventional method from melt containing copper monooxide as a supplement.

Highly efficient volume hologram multiplexing in thick dye-doped jelly-like gelatin.

Dye-doped jelly-like gelatin is a thick-layer self-developing photosensitive medium that allows single and multiplexed volume phase holograms to be successfully recorded using pulsed laser radiation. In this Letter, we present a method for multiplexed recording of volume holograms in a dye-doped jelly-like gelatin, which provides significant increase in their diffraction efficiency. The method is based on the recovery of the photobleached dye molecule concentration in the hologram recording zone of gel, thanks to molecule diffusion from other unexposed gel areas. As an example, an optical recording of a multiplexed hologram consisting of three superimposed Bragg gratings with mean values of the diffraction efficiency and angular selectivity of ∼75% and ∼21', respectively, is demonstrated by using the proposed method.

Holographic optical element to generate achromatic vortices

A compound holographic optical element to generate achromatic vortices with high efficiency, based on the combination of two volume phase holograms, is designed and constructed. This element is compact and easy to align. It has high damage threshold, so it can be used with ultraintense laser pulses.

The effect of decoloration on the properties of volume phase holograms based on silicate photothermorefractive glass

This paper discusses the decoloration process of volume phase holograms based on photothermorefractive (PTR) glass under the action of the second harmonic of the pulsed radiation of a neodymium laser. It is shown that the photodecoloration process increases the refractive-index modulation of PTR glass and reduces its absorption in the visible region.

Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm 2 and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm 2 is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation.

High power vortex generation with volume phase holograms and non-linear experiments in gases

An experimental method for the production of high power optical vortices by using volume phase holographic plates is presented. Experiments in air, N2 and Ar have been performed as an example of the method’s potential, observing non-linear effects and filamentation. Theoretical calculations support the conclusions.