SECONDMENTS

The objectives of the PhD is to build hybrid systems composed of functionalised glasses and liquid crystals. Planar devices and fibers are both goind to be studied. The first objective of this PhD is to oriente the molcules of liquid crystal with electrically functionalised glass surfaces by thermal poling. The second objective is to control the transmitted light by a fibre by the properties of liquid crystals.

For both of this goals we need to know how the liquid crystals behave in different environments. This aspect was studied in Bordeaux in the last months. A large amount of data needs to be processed now to extract the most interesting information. From this results we will design and manufacture a fibre integrating core, cladding, liquid crystals and electrods. The device will then be characterise. On the other hand we need to complete the surface analysis of poled glass by surface composition and surface topology characterisation.

• Design a glass fibre integrating metal electrod and a channel to add liquid crystal
• Fibre manufacture
• Fibre characterisation and data treatment
• Surface characterisation of poled glass (scanning electron microscope, atomique force microscope)
• Beginning of the paper writing

A new characterisation method based on polarised Raman spectroscopy had been etablished to be able to link the experiemental measurments to liquid crystals alignement. The first step was to prob the planar matrix of the Raman intensity  by controlling the incident and analysed light polarisation used for the mesurement. Then the orientation distribution function could have been be developed on the base of the Legendre polynomials.

This method has been first applied to references LC cells with planar and homeotropic alignment, respectively parallel and perpendicular to the substrate. The four Raman measurments were taken for each samples, the incident and analysed light polarisations variyng along X and Z as shown on the Figure 1a. Then the function G(θ) was calculated and the results are shown Figure 1b. Concering the planar alignment LC cell, one can observe maxima at 0 and 180 degres, meaning that the liquid crystals are aligned along the X axis. Regarding the homeotropic cell, the distribution function shows maxima in the four directions: 0, 90, 180 and 270 degres. Then, none of the Z and X axes are preferential and, with deduction the molecules are aligned perpendicular to this two directions, along the light propagation vector k.