Tkachenko G. Optical properties of a nanocomposite (mesoporous silicon)/(nematic liquid crystal) in near infrared and visible ranges

Thesis for a Doctor philosophy degree (Ph.D.) in physical-mathematical sciences by according to scientific specialty 01.04.05 - optics, laser physics. - V.N. Karazin Kharkiv national university, Kharkiv, 2012. Theoretical and experimental studies of a nanocomposite containing mesoporous silicon and nematic liquid crystal (NLC) are carried out in this thesis for the purpose of creation of tunable narrow-band optical filters based on such materials. The main attantion is paid to influences of temperature and electric field on the NLC molecules orientation in cylindrical pores. The NLC director field was calculated by solving the Frank equation for NLC molecules with the assumption of axisimmetrical escaped radial (ER) configuration. We have simulated the director field dependance on electric field, pore radius and molecular anchoring strength. As well the range of electrical tuning of a microcavity (MC) based on the investigated composite was calculated. Spectroscopic ellipsometry of mesoporous silicon and silica films, infiltrated with NLC E7, proved to be informative only for the silica film. The obtained thermal dependencies of refractive indices indicate ER director configuration of NLC in mesopores. Revercible tuning of a thermooptical MC based on the nanocomposite (mesoporous silicon)/(NLC E7) by means of a hot-stage of powerful green laser has beed observed. The NLC molecular anchoring strength in Si mesopores was estimated. Haller's approach was successfully applied for the approximation of the measured NLC effective refractive index depended on temperature.