Photopolymer characterization by high frequency pulsed laser

Maximizing phase modulation in photopolymers remains a challenge in order to use these materials to fabricate photonics devices. Different material compositions and irradiation conditions have been studied in order to achieve it. One of the main conclusions has been that with continuous laser exposure better results are achieved. However, our results show that higher phase modulation can be achieved using pulsed laser. The study has been done with crosslinked acrylamide-based photopolymers (AA/PVA), Biophotopol and Holographic Polymer-Dispersed Liquid Crystals (HPDLC) exposed with a pulsed laser (532 nm). Thus, phase modulation increases of 8-15% have been achieved between pulsed laser and continuous laser exposure, with a maximum phase depth of 3π radians in AA/PVA, ~3π/2 in Biophotopol and ~π in H-PDLC. This opens the door to the use of this photopolymer in large-scale manufacturing, such as H-PDLC photopolymers to fabricate tunable lenses using the laser-induced direct transfer (LIFT) technique.The work was supported by the “Generalitat Valenciana” (Spain) (IDIFEDER/2021/014, cofunded by European Union through the FEDER Programme, projects PROMETEO/2021/006 and projects BEST/2021/021), “Ministerio de Ciencia e Innovación” of Spain (projects FIS2017-82919-R; PID2019-106601RB-I00), by the ‘‘Universidad de Alicante’’ (UATALENTO18-10; ACIE-20-10), and Marie Skłodowska Curie Postdoctoral Global Fellowship “FOCUSIS” grant agreement 844977

Photopolymers comparison for see-through applications

We have developed a coupled waveguide system based on slanted transmission gratings recorded in photopolymers. In this work we compare the behavior of four different photopolymers for this high demanded application.This work was supported by the “Generalitat Valenciana” of Spain (projects PROMETEO/2021/006 and IDIFEDER/2021/014, cofunded by European Union through the FEDER Programme) and by the Universidad de Alicante, Spain (UATALENTO18-10; ACIE-20-10)

Manufacturing reflection holographic couplers for see-through applications recorded in photopolymers without prisms: an experimental validation

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material, as they are well-suited for the intended see-through application. Moreover, Kogelnik’s theory fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced gratings exhibit the correct properties to work as a coupler.Work supported by the “Generalitat Valenciana” (Spain) project PROMETEO/2021/006 and “Ministerio de Ciencia e Innovación” of Spain (project PID2021-123124OB-I00

Diffraction efficiency in reflection holograms stored in photopolymers doped with metallic nanoparticles

In the last few years, the interest in storing volume holograms in photopolymers has increased enormously due to their applications in industry, the medical field, security, or renewal energy among others. The production of environmentally compatible photopolymers is one of the main focuses of Holography research. In this work, we have studied how to increase the diffraction efficiency of reflection holograms stored in a low-toxicity PVA-based photopolymer called Biophotopol. The holographic material has been doped with different types of nanoparticles (NPs) to achieve an increase in the refractive index modulation during the recording stage. Metallic NPs, obtained by physical and electrochemical methods have been used. The results obtained with all of them have been compared as a function of the concentration used, the size of the NPs, and the stabilization method used for their synthesis. A considerable increase in diffraction efficiency has been achieved by using NPs in the low-toxicity material. By using high refractive index NPs, the average refractive index of the holographic material increases and consequently the diffraction efficiency.This research was funded by Generalitat Valenciana, Spain, under projects PROMETEO/2021/006, IDIFEDER/2021/014 (co-funded by European Union through the FEDER Program) and CIDEXG/2022/60; Universidad de Alicante, Spain, under project UAFPU20-23 and Ministerio de Ciencia e Innovación, Spain, under projects PID2019-106601RB-I00 and PID2021-123124OB-I00

Analysis of the recording of Fibonacci lenses using photopolymers with 3-D diffusion model

In the present work, a 3-Dimensional diffusion model is proposed to predict the main properties of Diffractive Optical Elements (DOEs), recorded in photopolymers, including refractive index modulation and the evolution of the transverse intensity distribution. The model enables the selection of appropriate material characteristics based on the intended application of the DOE. Specifically, a PVA/AA photopolymer based on acrylamide is simulated using the proposed model, considering coverplating and index matching systems to mitigate the effects of thickness variation. In order to compare its properties using the suggested model, the simulation focuses on a Fibonacci Lens and the dependece of the intensity on the polymerization rate. Accordingly, axial intensity pattern is represented to prove the bifocal-behaviour of these diffractive lenses.Funded by the “Generalitat Valenciana” (Spain) (ID- IFEDER/2021/014, cofunded by EU through FEDER Pro- gramme; PROMETEO/2021/006 and INVEST/2022/419 financed by Next Generation EU), “Ministerio de Ciencia e Innovación” (Spain) (PID2021-123124OB-I00)

Study of the conservation of different holograms sandwiched between glasses

Photopolymers are designed and engineered with versatile applications including optics and photonics. Holography is one of the classical porpoises that use photopolymers as holographic recording materials. The success of these materials can be seen in the market with the photopolymer fabricated by Covestro. Some of these holographic applications require a long-time life of the holograms recorded in photopolymers. Nevertheless, initial tests of Covestro holograms show significant degradation after less than one year of exposure even after sealing and degradation occurs under solar light exposition. In this sense, it is important to perform deeper studies of the different possibilities for hologram conservation. Usually, the first step after recording is the material cure, with UV or visible light, to eliminate the residual dye and monomer. With this process high efficiency holograms can also be obtained. Afterwards, an index matching technique can be used to cover the material with a glass or it is possible the application of aerosol sealant. In this paper we analyze the introduction of holograms between two glasses linked by pressure, using Bayfol HX 200 from Covestro as the recording material. In order to characterize the process, four different spatial frequencies were tested, which were stored either by transmission or reflection schemes. The data of the reconstruction step has been measured before and after the encapsulation. In addition, multiple holograms have been superposed in the same glass, where we have found that shrinkage is more significant.The work was supported by the “Generalitat Valenciana” (Spain) project PROMETEO/2021/006 and by the ‘‘Universidad de Alicante’’ (UATALENTO18-10; ACIE-20-10). Generalitat Valenciana (Spain) (IDIFEDER/2021/014, cofunded by European Union through the FEDER Programme and “Ministerio de Ciencia e Innovación” of Spain (project PID2021-123124OB-I00)

Second comment on 'Maxwell's equations and Lorentz transformations'

Aguirregabiria et al (2022) Eur. J. Phys. 43 035603 obtained the Lorentz transformations by assuming the invariance of Maxwell's equations in vacuum under inertial transformations. However, they do not initially assume that these transformations must be linear. Later, Redzic (2022) Eur. J. Phys. 43 068002 indicates that it is necessary to explicitly assume the linearity of these transformations to avoid a remarkable and surprising result. Now it is shown that it is not necessary to make the assumption that the transformation equations between inertial reference frames must be linear, but that this linearity is a consequence of the homogeneity of space-time.This work was supported by the Generalitat Valenciana (Spain) under the project (PROMETEO/2021/006)

Precise-Integration Time-Domain for Optical Anisotropic Media

The Precise-Integration Time-Domain (PITD) formulation permits to break through the Courant- Friedrich-Levy (CFL) condition, which limits the accuracy, stability, and indirectly the applicability of the traditional Finite-Difference Time-Domain (FDTD) method. This characteristic permits considering larger time steps than the largest one fixed by the CFL condition. As the conventional FDTD scheme, PI also takes the spatial derivatives through the central finite-difference scheme. This step sets up a set of ordinary differential equations (ODEs) that are solved using the PI Technique. Here, the technique is applied to different periodic and anisotropic optical media. More precisely, to anisotropic polarization gratings (PG). PG is based on a periodically patterned, uniaxial birefringence in the grating plane that modulates the polarization of light instead of its amplitude.The work was supported by Generalitat Valenciana (projects PROMETEO/2021/006; IDIFEDER/2021/014, cofunded by European Union through the FEDER programme)

See-through display based on commercial photopolymer: Optimization and shrinkage effects

AbstractNowadays augmented reality, 3D Image, mixed reality and see-through applications are very attractive technologies due to their great potential. Holographic optical elements can provide interesting solutions for injection and extraction of the image in the waveguides that are part of the see-through devices. We have developed a coupled waveguide system based on slanted transmission gratings recorded in manufactured photopolymers. In this work we optimize our schedule to a commercial photopolymer for this high demanded application. We demonstrate that high diffraction efficiencies can be obtained if we optimize the recording geometry, recording intensity and recording time for this material. In addition, we study the effects of shrinkage in our holographic system. In general shrinkage is an important drawback for holographic applications, nevertheless we demonstrate how shrinkage can help these systems open new possibilities. Lastly, we show how to significantly improve the quality of the guided image

Capacitor connected to an alternating voltage: Maxwell's equations, Poynting's theorem and oscillating L-C circuits

The behaviour of a parallel-plate capacitor connected to a sinusoidal alternating voltage is analysed and the electric and magnetic fields, as well as the electric and magnetic energies inside the capacitor are obtained. Aspects related to Maxwell's equations, the Poynting vector and the conservation of electromagnetic energy are also discussed. Under certain conditions the electromagnetic energy stored in the capacitor remains constant and the behaviour of the capacitor at high frequencies is like that of an oscillating L-C circuit consisting of an inductor and a capacitor. The general situation is considered, valid for both low and high frequencies, and what is discussed here is of interest to students of an undergraduate electrodynamics course.This work was supported by the Generalitat Valenciana (Spain) under Project PROMETEO/2021/006), by the Ministerio de Ciencia, Innovación y Universidades (Spain), predoctoral contract (FPU22/04316, J.J. Sirvent-Verdú) and the Universidad de Alicante (Spain), predoctoral contract (UAFPU20-23, T. Lloret)