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English summary
Modelling and implementation of holographic projection screens
Today projection displays have gained wide acceptance in the professional sector (replacing
the overhead slide projector), as well as in the hobby sector. Especially here more and
more ”home cinemas” and other wide-screen applications have become popular due to
enhancements in projection technology and dropping prices.
One of the main drawbacks of front- and rear-projection systems, however, is the drop in
contrast ratio and color saturation caused by ambient light. Typical light levels of darkened
conference rooms (around 80 lux) are already sufficient to decrease the contrast ratio of
front projections down to values as low as 20:1.
A possible solution for this problem is the projection onto a holographic screen. Basically,
this is a large, image-plane hologram of a conventional projection surface. Due to the
inherent spectral and angular selectivity of volume holograms, these can be optimized
to scatter projected light into the direction of the observer, but let ambient light pass
through unaltered. Since no such light is scattered to the observer, black or transparent
screen surfaces can be produced which maintain the contrast ratio of the projector.
Although screens based on holographic principles are already commercially available for
rear-projection, the popular application of front-projection is not yet accessible for holographic
screens. This is mainly due to the relatively small spectral bandwidth of reflection
holograms (typically 10nm-20nm), which imposes major difficulties for efficiency and color
rendition when replayed with broad-band projection sources. A second problem for holographic
front and rear-projection screens is the recording process, which limits the size of
those holograms to the order of less than 1m 2 .
In this thesis an approach to overcome the stated problems and drawbacks of holographic
front-projection screens is presented. The problem of wavelength selectivity is modelled
by use of Kogelnik’s theory of coupled waves; numerical calculations employing measured
projector spectra are used to estimate color rendition and efficiency of RGB holograms. The
characteristics of holographic media are thoroughly investigated in order to be included
into these calculations, yielding a set of recording instructions which can be used for the
production of color saturated and efficient RGB front-projection screens.
Chapter 1 starts off with an introduction into the principles of holographic projection
screens and the required recording processes.
In chapter 2, an introduction into holography and the analytical treatment for the description
of volume holograms based on Kogelnik’s theory is given. Furthermore, the basics of
scanned holographic exposures and the reproduction and measurement of color are explained.
Chapter 3 conducts a detailed investigation of holographic recording materials (silver halides
and photopolymers) regarding sensitivity, film speed, thickness, refractive index,
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