The influence of the ionic contribution to electro-optic effect in nematic liquid crystals aligned with
conducting polymers was investigated. The study has been carried out on symmetric cells filled with nematic liquid
crystal 5CB having positive dielectric anisotropy. Planar alignment of the nematic director has been imposed using
unidirectional rubbed conducting polymer substrates, namely polypyrrole (PPy) doped with different types of ions.
Employing a typical experimental set-up, the intensities of linearly polarized He-Ne light beams, transmitted through
each cell when submitted to an external electrical excitation, were measured. Fast electro-optic response times
measured at switching off the electric field are probably related to the accumulated charge distributions at nematic-conducting
We present a new geometry for edge-pumping of a solid-state microchip laser. This design, which consists of a thin-disk
gain crystal surrounded by a diffusion bonded undoped material that guides the pump light, allows a good thermal heat
management by reducing the thickness of the gain media, whereas the pump optics is kept simple. The upper surface of
the gain media has concave-spherical shape that allows easy confinement of the pumping power to laser gain media
thinner than 100 μm. Simulations show that more than 0.95 of the pump radiation with uniformity coefficient in excess
of 0.96 can be absorbed in an Yb:YAG/YAG composite device that has a 50-μm thick, 10-at.% Yb:YAG of 3 mm
Photoinduced molecular reorientation in dye-doped liquid crystal cells has been studied for a set of azodyes with a
"pump-probe" optical device. The rotating angle of the nematic director as a function of irradiation time has been
calculated. The lateral chemical groups of the azo-dye molecules have not an important influence on the orientation
effect; this aspect supports the idea that the trans-cis photoisomerization of the dye molecules is the predominant
mechanism responsible for the molecular reorientation in azo-dye-doped liquid crystal systems.
The output characteristics of a continuous-wave flash lamp pumped Nd:YAG laser, passively Q-switched by Cr4+:YAG are reported. In order to control the small-signal transmission of the passive Q-switch, a new method, which made use of a miniature laser placed out of the resonator, is described theoretically and proved experimentally. Further, the combination of a Cr4+:YAG passive Q-switch and an acoustooptic Q- switch that work together in a Nd:YAG CW pumped laser was investigated. With a two-rod resonator and a Cr4+:YAG crystal as saturable absorber, an average laser output power over 180W was reached. The pulse-to-pulse stability was 1%. Folded resonator was used in order to obtain intracavity second harmonic generation in active and passive Q-switch mode.
The electrooptical properties of some SSFLC devices with high spontaneous polarization liquid crystals are presented. The switching time was determined as function of electric field strength and a.c. frequency. Using the switching time the rotational viscosity (gamma) $curly phi was determined. The results are explained by considering the spectacular molecular relaxation, known as Goldstone mode. The surface stabilized ferroelectric liquid crystal (SSFLC) devices offer memory (bistable) capability, fast response speed and sharp threshold and have a variety of applications in electronics.
The behavior under magnetic fields of new types of ferronematics is examined. First, by using both optical and electrical method, an increase in the critical field for Freedericksz transition was noticed in cells containing ferronematics. Second we give an explanation of the relaxation processes occurring in ferronematics when the magnetic field was suddenly varied. When ferronematics are involved, the relaxation phenomena are described by lower time constants when compared to those of pure nematics.