Diffractive optical elements with an increased angular and wavelength range of operation for application in solar collectors

Abstract

A holographic device characterised by a large angular and wavelength range of operation is under development. It aims to improve the efficiency of solar energy concentration in solar cells. The aim of this study is to increase the angular and wavelength range of the gratings by stacking three layers of high efficiency gratings on top of each other so that light from a moving source, such as the sun, is collected from a broad range of angles. In order to increase the angle and the wavelength range of operation of the holographic device, low spatial frequency of holographic recording is preferable. Recording at low spatial frequency requires a photopolymer material with unique properties, such as fast monomer/monomers diffusion rate/rates. An acrylamide-based photopolymer developed at the Centre for Industrial and Engineering Optics has been used in this study. This material has fast diffusion rates and has previously demonstrated very good performance at low spatial frequency, where gratings of 90% diffraction efficiency at 300 lines/ mm spatial frequency were recorded in layers of 75 μm thickness. This paper will study the angular selectivity of a device consisting of stacked layer of Difftactive Optical Elements ( DOEs) recorded at range of angles at spatial frequency of 300 lines/mm with recording intensity of 1 mW/cm 2 . The optical recording process and the properties of the multilayer structure are described and discussed.