A Comprehensive Study of Photorefractive Properties in Poly(ethylene glycol) Dimethacrylate— Ionic Liquid Composites

Abstract

A detailed investigation of the recording, as well as the readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids is presented. Gratings with a period of about 5.8 micrometers were recorded using a two-wave mixing technique with a coherent laser beam of a 355-nm wavelength. A series of samples with grating thicknesses d0=10…150 micrometers, each for two different exposure times, was prepared. The recording kinetics, as well as the post-exposure properties of the gratings were monitored by diffracting a low intensity probe beam at a wavelength of 633 nm for Bragg incidence. To obtain a complete characterization, two-beam coupling experiments were conducted to clarify the type and the strength of the recorded gratings. Finally, the diffraction efficiency was measured as a function of the readout angle at different post-exposure times. We found that, depending on the parameters, different grating types (pure phase and/or mixed) are generated, and at elevated thicknesses, strong light-induced scattering develops. The measured angular dependence of the diffraction efficiency can be fitted using a five-wave coupling theory assuming an attenuation of the gratings along the thickness. For grating thicknesses larger than 85 microns, light-induced scattering becomes increasingly important. The latter is an obstacle for recording thicker holograms, as it destroys the recording interference pattern with increasing sample depth. The obtained results are valuable in particular when considering PEGDMA-ionic liquid composites in the synthesis of advanced polymer composites for applications, such as biomaterials, conductive polymers and holographic storage materials.

Light- and Neutron-Optical Properties of Holographic Transmission Gratings from Polymer-Ionic Liquid Composites with Submicron Grating Spacing

“…Still, we noticed a troublesome inhomogeneity of the grating quality across the recording area, similar to as shown in an earlier work (Figure 10 of [17]). In order to make use of the materials investigated in this work for reliable optical elements, this inhomogeneity has to be reduced.…”

“…One could try to replace the UV photoinitiator with one in the visible range to make efficient use of the higher powers available with lasers of visible wavelengths. It remains to be tested how different combinations of power and recording time affect the resulting modulation in a diffusion-rate-controlled polymerization process [17]. An additional problem arises with thicker samples in the form of air or other inclusions between the sample material and its glass coating due to shrinkage during polymerization.…”

“…This work focuses on another composite material that makes use of ionic liquids as additives to a photopolymer [14,15,16]. In a previous work, the suitability of this polymer-ionic liquid composite as recording media for structures in the 5–10 μm range was examined [17]. The obtained results allow us to make use of the good resolution of the material in order to write thick holographic transmission gratings with a submicron grating spacing of Λ=480 nm.…”

Monte-Carlo simulation of neutron transmission through nanocomposite materials for neutron-optics applications

“…This promising result encourages further pursuit of the development of diffractive optical elements for cold and very-cold neutrons based on nanocomposite materials. Furthermore, all the results are considered to be valid also for other material classes of similar chemical composition [8,9], which are being tested for use in neutron optics.…”

“…1(b)] have recently been demonstrated to exhibit varying neutronpolarization properties as a function of the external magnetic field [8], which might pave the way to inexpensive, business-card size polarizing beam splitters for neutrons. Recently, we expanded our search for suitable materials further to include mixtures containing ionic liquids [9].…”