Biomedical subjects

C Umeton

Publications and source records attributed to C Umeton.

8 recordsLinked to original sources

PubMed2005

Self-healing generation of spatial solitons in liquid crystals.

We demonstrate that, in suitably designed cells with undoped nematic liquid crystals, extraordinary-wave spatial solitons can be excited at every applied voltage without adjustments in the input polarization. Their walk-off, hence direction of propagation, is externally controlled over angles as large as 7 degrees. The results pave the way not only to polarization-forgiving generation but also to voltage readdressing of these extraordinary-wave nematicons.

Journal Article↗

PubMed2004

Electro-optic properties of switchable gratings made of polymer and nematic liquid-crystal slices.

We report the diffraction properties at wavelengths of 632.8 and 1550 nm for volume transmission gratings made of a sequence of continuously aligned nematic liquid-crystal layers separated by isotropic polymer slices. The gratings are generated by holographically curing a solution of liquid crystal diluted in an isotropic prepolymer by means of a laser beam at a wavelength of 352 nm with a total intensity of approximately 10 mW/cm2. A diffraction efficiency of 98% was measured, and an electric field as low as 5 V/microm switches off the phase grating. Measured angular spectra are fitted by use of the modified coupled-mode theory including the effects of grating birefringence.

Journal Article↗

PubMed2004

Dynamical behaviour of holographic gratings with a nematic film--Polymer slice sequence structure.

We have studied the dynamical response of a new kind of holographic grating to a pulsed electric field. The structure, named POLICRYPS, consists of a sequence of homogeneous polymer slices separated by liquid-crystal films. We have found that both the rise and fall response times depend on the pulse duration and amplitude of the applied electric field. We propose a phenomenological explanation for this behaviour, outlining the possibility of getting response times of the order of 100 micros by properly choosing the pulse shape. Results are very interesting for developments in which POLICRYPS gratings could be proposed as basic elements in photonic devices for telecom applications, and induce to a deeper analysis of the microscopic interaction between liquid crystal and polymer interfaces in these samples.

Journal Article↗

PubMed1996