My history in laser science
“One does not, by knowing all the physical laws as we know them today, immediately obtain an understanding of anything much.”
Richard Feynman (1918-1988)
I originally trained as scientist, and spent some postgraduate time doing a doctoral thesis in Liquid crystal Optics. I keep a copy of the published thesis and links to papers/talks online in case they are useful to anyone in the field.
Research topic
My postgraduate research was based in the Functional Optical Materials Group in the School of Physics and Astronomy. The group was focussed on research into optical devices using liquid crystals, specifically photorefractive diffraction gratings. A photorefractive material is one which changes it properties when light is incident on it and we were interested in this effect in liquid crystals.
Liquid crystals have some very interesting properties, and can be very beautiful to look at. Because they are not rigid like a solid, the molecules in liquid crystals can move around so when they feel a force from an applied electric field, they tend to line up with it (this is how LCDs work).
In our case we have a photoconductive material on the surface our our liquid crystal cell which means we can let electric field into the LC only where we illuminate it, and by creating a light interference pattern with two laser beams, we can reorient the molecules in the LC in stripes to make a diffraction grating. Such materials could have practical applications, as they could offer a cheap alternative to current optical switches and amplifiers used in the telecoms industry.
Thesis: Surface effects in liquid crystal-polymer structures, theoretical modelling and experiments
It has been proposed that surface effects play a large role in the reorientation of liquid crystal-polymer structures. Surface charge layers build up at the liquid crystal-polymer interface, screening the LC bulk from applied electric field. Photoinduced charge recombination occurs under illumination and allows the electric field to penetrate into the LC bulk, causing reorientation and creating a refractive index grating. If the phase shift between the index grating and the interference pattern is non-zero, beam coupling can occur. This thesis presents simulations of the reorientation mechanism and attempts to validate these models by comparing to experimental results.
Presentations
- Spatially non-uniform director profiles in liquid crystal-polymer structures International Liquid Crystal Conference 2006 - Boulder Colorado, Poster presentation (accepted)
- Spatially non-uniform director profiles in liquid crystal-polymer structures British Liquid Crystal Society Annual Meeting 2006, York UK, Poster presentation (April 2006)
- Surface charge Fields and reorientation in liquid crystal-polymer structures, Physics 05: A century after Einstein, Poster presentation (April 2005)
Publications
- Surface screening layers and dynamics of energy transfer in photosensitive polymer-liquid crystal structures, Mol. Cryst. Liq. Cryst., Vol. 446, pp. 261-272, 2006
- Proceedings of SPIE, Optics & Photonics, 31 July - 4 August 2005, San Diego, California USA
- Proceedings of SPIE, 5621, 133 (2004)
