Reconfigurable Surface Micropatterns Based on the Magnetic Field-Induced Shape Memory Effect in Magnetoactive Elastomers

A surface relief grating with a period of 30 µm is embossed onto the surface of magnetoactive elastomer (MAE) samples in the presence of a moderate magnetic field of about 180 mT. The grating, which is represented as a set of parallel stripes with two different amplitude reflectivity coefficients, is detected via diffraction of a laser beam in the reflection configuration. Due to the magnetic-field-induced plasticity effect, the grating persists on the MAE surface for at least 90 h if the magnetic field remains present. When the magnetic field is removed, the diffraction efficiency vanishes in a few minutes. The described effect is much more pronounced in MAE samples with larger content of iron filler (80 wt%) than in the samples with lower content of iron filler (70 wt%). A simple theoretical model is proposed to describe the observed dependence of the diffraction efficiency on the applied magnetic field. Possible applications of MAEs as magnetically reconfigurable diffractive optical elements are discussed. It is proposed that the described experimental method can be used as a convenient tool for investigations of the dynamics of magnetically induced plasticity of MAEs on the micrometer scale.

Simple method to evaluate the pixel crosstalk caused by fringing field effect in liquid-crystal spatial light modulators

In this work we provide a simple experimental method to measure and evaluate the pixel crosstalk in phase-only liquid-crystal displays caused by the fringing field effect. The technique is a reverse engineering method that does not require information about the microscopic physical parameters of the liquid-crystal material or details of the fabrication and electronics of the display. Instead, it is based on the overall effect on the diffraction efficiency of displayed binary phase gratings as a function of the addressed gray level. We show how the efficiency of the zero (DC) and first diffraction orders provides valuable information enough to identify and quantify the pixel crosstalk. The technique is demonstrated with a modern phase-only liquid-crystal on silicon (LCOS) spatial light modulator (SLM), illustrating the limitations that this effect imposes to the spatial resolution of the device and providing quantitative measurement of the impact on the diffraction efficiency.

2D scanning system of the acousto-optical deflector with high diffraction efficiency

The paper considers advantages and special features of an acousto-optic method for the development of a functional device for spatial and temporal control of laser light and reports results of investigations to create a two-directional acousto-optic laser scanner with diffraction efficiency as high as 80 percent or better. An acousto-optic deflector on a paratellurite crystal operating under the Bragg diffraction condition with a lithium niobate piezoelectric acoustic transducer was developed and tested experimentally. The results of this work can serve as a basis for the development of prototype functional acousto-optic devices for spatial and temporal control of laser light and their application to create laser television images.

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.

Highly Efficient Double-Layer Diffraction Microstructures Based on New Plastics and Molded Glasses

Within the framework of rigorous diffraction theory, the maximum possible incidence angles of radiation on two-layer sawtooth relief-phase microstructures in the visible (0.4 ≤ λ ≤ 0.7 μm) spectral range are compared. Optical materials for the layers of these microstructures are selected from a database of 47 plastics and 165 molded glasses. It is shown that when the ratio of the spatial period of the microstructure to the effective depth of the relief is greater than 20, the achievable angles within which the diffraction efficiency exceeds 0.95 lie in a wide range from 18.5° to 40.5° for single-relief structures and 7.5° to 22.3° for structures with two internal reliefs. The best results for purely plastic microstructures are obtained when the plastic CMT and the indium tin oxide nanocomposite in polymethylmethacrylate are used.