Since 10 years spatial optical solitons are studied for application in optical steering and routing. We propose here another
potential use of solitons: a localized spectral probe in colloids. We show the feasibility of this concept by collecting the
fluorescence signal escaping from in a cell filled with a mixture of liquid crystal (5CB) and dye (quinizarin), excited
either by a spatial soliton obtained by thermal self-focusing or by a freely propagating beam. We find that the
fluorescence signal collected at the output of the soliton is larger than the one collected on the same optical path in the
linear regime. A model based on waveguide considerations confirms such a behavior. Finally we discuss how
polystyrene particles can be detected in colloids by using spatial solitons.
Mixing non-local process in a material with non-local response can yield to interesting phenomena. This is the case of spatial optical solitons excited in liquid crystals. It has been shown that spatial optical quasi-soliton can be generated either via a heat transfer process or a molecular reorientation. In both cases, light keeps propagating in the waveguide it created. Different parameters can be adjusted to optimize this waveguide and as a result the propagation of the quasi-soliton. Prior to control those parameters, it is interesting to measure the global non locality, i.e. the extension of the beam together with the induced index profile. Herein, it is reported first the main results on quasi soliton in liquid crystals, some technique to measure the induced index distribution. Then, a new method, based on Raman spectroscopy, is proposed to measure simultaneously the beam intensity distribution and the induced molecular reorientation in the case of a soliton generated via reorientation nonlinearity of a nematic liquid crystal. Finally, it is shown how the non-locality can be controlled and used. The case of a curved waveguide obtained this way is reminded.
We studied electro-optical characteristics of the liquid crystal (LC) cell with weak planar anchoring of the director with bounding substrates. The weak surface anchoring let us to decrease the cell driving voltage. Moreover, because of the absence of the strong subsurface director deformations, the cell could operate in the Mauguin regime. Using these we proposed a new type of the LC switching mode--the in-plane sliding mode. We realized this mode in the LC cell comprising of one reference substrate with strong director anchoring and one photoaligning material-covered substrate with weak anchoring.
Refractive indices of two nematic liquid crystals, 5CB and 5PCH, were measured from the 400- to 800-nm region at various temperatures. Results fit the three-band model well. Through comparisons, the contributions of σ and π electrons to the refractive indices and birefringence of uniaxial liquid crystals are evaluated quantitatively. These physical insights are useful for tailoring liquid crystal molecules with proper refractive indices.