Abstract
A holographic device characterised by a large angular range of operation is under development. The aim of this study is to increase the angular working range of the diffractive lens by stacking three layers of high efficiency optical elements on top of each other so that light is collected (and focussed) from a broader range of angles. The angular range of each individual lens element is important, and work has already been done in an acrylamide-based photosensitive polymer to broaden the angular range of individual elements using holographic recording at a low spatial frequency. This paper reports new results on the angular selectivity of stacked diffractive lenses. A working range of 12° is achieved. The diffractive focussing elements were recorded holographically with a central spatial frequency of 300 l/mm using exposure energy of 60 mJ/cm2at a range of recording angles. At this spatial frequency with layers of thickness 50 ± 5 µm, a diffraction efficiency of 80% and 50% was achieved in the single lens element and combined device, respectively. The optical recording process and the properties of the multilayer structure are described and discussed. Holographic recording of a single lens element is also successfully demonstrated on a flexible glass substrate (Corning(R) Willow(R) Glass) for the first time.
Highlights
Photopolymers are fast becoming one of the most popular recording media for holographic applications for a variety of reasons; they have excellent holographic characteristics, such as high refractive index modulation, large dynamic range, good light sensitivity, real time image development, high optical quality, and low cost
In this work we present low spatial frequency photopolymer holographic lenses stacked together in order to increase the angular range of the focussing device
The following results show how diffraction efficiency varies with angle of incidence for individual holographic focussing elements, recorded in photopolymer on plastic substrates, as well as a combined stack of three elements
Summary
Photopolymers are fast becoming one of the most popular recording media for holographic applications for a variety of reasons; they have excellent holographic characteristics, such as high refractive index modulation, large dynamic range, good light sensitivity, real time image development, high optical quality, and low cost. An ideal holographic recording material should have the following properties: high sensitivity to available commercial wavelengths, high spatial resolution for improved quality recording, linear response to recording intensities, and low noise, that is, a fine grain structure to reduce scatter effects. In applications where low angular selectivity is necessary, the ability to record at lower spatial frequencies is beneficial. Considerations regarding material flexibility, substrate flexibility, substrate thickness, substrate optical properties, and good adhesion are of significance, when stacking layers
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