Margareta Socaciu

DISPERSION CURVES COMPUTED FROM CHANNELED DIFFRACTION SPECTRA OF LIQUID CRYSTALS

Using a new version of the Talbot-Rayleigh method we recorded the I (λ) channeled spectra of uniaxial nematic liquid crystal at different temperatures. We derive the theoretical expression of I (λ) that involves a three-band model for the refractive indices, which is then fitted with the experimental data by a nonlinear optimization procedure. As a result, we compute the dispersion curves no, ne, Δn, their temperature dependencies, and the band contributions.

Build-up of thermoelectrets at phase transitions in fatty acids

Abstract The thermotropic mesomorphism of different fatty acids is illustrated by the thermodielectric effect and by micro structural observations. The fatty acids which are studied (arachidic, lauric and elaidic acids) have an initial space charge. The thermodielectric effect is due to charge separation and consists in the appearance of noticeable variations of electric current intensity as a function of the temperature at phase transitions.

Light scattering in liquid crystals

In this paper we study the light scattering on the different mesophases of TBBA-CM mixture. We used He-Ne laser radiation and we derived a simple theoretical model of the diffusion process. The results are in good agreement with the data provided by other experimental methods.

Phase transitions in smectic liquid crystals by thermodielectric effect

Abstract In this paper we confirm the existence of the thermodielectric effect at phase transitions of mesogenes with smectic phases: terephthal-bis-butyl-aniline (TBBA) and cholesteryl myristate (CM). Significant sudden variations of the electric current were detected at all phase transitions. Thus, transition temperatures are identified in good agreement with literature. We have also determined the polymorphism of the mixture TBBA 25% + CM. 75% by weight.

ORDER PARAMETER FROM (p-ETHOXYBENZYLIDENE-)-p-n-BUTYLANILINE CHANNELED SPECTRA

The dispersion of refractive indices and birefringence of EBBA were determined at different temperatures and the band contributions to these dependencies were computed. An improved Talbot–Rayleigh experimental setup was used and, in order to increase the accuracy and minimize the computation time, a new data processing method was proposed. The temperature dependence of the order parameter and of the correction factor g, originating from the anisotropy of the local field, were computed.

Temperature dependencies of optical parameters from EBBA channeled spectra

Starting from the experimental channeled spectra I of the nematic EBBA liquid crystal and using a nonlinear optimization algorithm, we computed the dispersion curves of the ordinary and extraordinary indices, of the birefringence and the band contributions to these dependencies, as functions of the temperature. The theoretical interpretation of the spectra and the data processing technique allowed us to compute the realistic variation of the order parameter S and correction factor g with the same external parameter.

Nonlinear processes in laser radiation absorption on metallic surfaces

We performed both experimental and theoretical studies on the laser radiation absorption coefficient of a copper surface. A theoretical model for the computation of the absorption coefficient was elaborated for two-layer case (metal-oxide), taking into account the nonlinear processes which govern the dynamics of the temperature and of the widths of the layers. The experimental data and the simulation results proved to be in a very good agreement.

Multiple Layer Interference on Tbba-Cm Liquid Crystal Mixture

Abstract The new thermo-electro-optical effect consist of visible spectra colours changing under a. d.c. electric field in a time periodical temperature variation around the given temperature value. This effect was remarked using a liquid crystal mixture TBBA-CM. In this paper we explain this effect by multiple layer interference. Analysing the theoretical results we obtained a good agreement with the experimental data.

Population/depopulation kinetics study for the energetic levels of krypton using resonantly-enhanced multiphoton ionization spectroscopy

Using REMPI spectroscopy methods, the gases energetic levels population can be directly investigated performing a variable time delay between one first excitation and a monochromatic reexcitation, and an accordable wavelength. The time evolution of the 1P1 and 3P0 energetic level population of krypton is described, as a result of 1S0 yields 1P1 excitation and a kinetic model is proposed for the 1P1 level decay through excited excimer states.

Polarized light interference in mixture of liquid crystals

Heating the matrix of terephtal-bis-butyl-aniline and cholesteryl myristate in time periodical temperature regime (sine-shape) under a d.c. electric field, we remarked the visible spectra colors changing at the light polarizing microscope. We noticed that the electrical current intensity variations in time has the same period and the same shape temperature variations through the cell with liquid crystal mixture. In this paper we explained this effect by light polarized interference.