# 06 - Holography based disordered structures for tailored scattering

**Source**: https://www.cs.tum.de/spp1839/projects/1st-period-2015-2018/06.html
**Parent**: https://www.cs.tum.de/spp1839/projects.html

We propose a holographic approach to the
formation of disordered photonic structures. Holographic methods were
used previously to manufacture 3D photonic crystal structures using
multiple beam interference or sequential two beam exposure. We propose
to use the second technique and add disorder to it by choosing random
directions of the counter propagating plane waves and random difference
between the phases of two respective waves. The disordered photonic
structure can be obtained directly by index variation in the exposed
photorefractive material or by selective etching or dissolution of a
photoresist thus providing index contrast between air filled pores and
the undissolved material. For example, we show that sequential exposure
with counter propagating plane waves with random orientation and the
same wavelength can lead to a disordered structure resembling that
obtained by spinodal decomposition.

The main part of the approach is the tailored
scattering of the incident light from the previously written multiple
random gratings in the structure. This scattering is visualized using
the Ewald sphere construction usually applied in X-ray diffraction. The
main objective of the proposal can be separated in three partial
goals. First, the application of the Ewald sphere construction will be
studied to describe the problem of optical scattering in disordered
holographic structures. Second, experimental methods to write
disordered holograms will be developed. The photoresist or the
photorefractive material will be exposed to a sequence of two wave
interferences or a single exposure by a plane wave and diffuse light.
Third, the following optical effects should be demonstrated:
non-iridescent structural colour and frequency and direction dependent
scattering elements for diffuse reflection or light trapping. The three
effects will be characterised with respect to their spectral and
directional properties.The theoretical results of this proposed project
will lead to development of a simple model for scattering in
disordered structures with small refractive index contrast. The
experimental work will provide a technological contribution to the
development of structural colour, transparent displays and light
trapping.

## Contributors

- [Prof. Manfred Eich](https://www.tuhh.de/oem/startseite.html)
- Dr. Alexander Petrov
- Lukas Maiwald

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