Influence of anthraquinone dyes on optical reorientation of nematic liquid crystals

Abstract

Optical reorientation measurements in dye-doped nematic liquid crystals are reported. The dye-induced optical torque exceeds significantly the normal optical torque for all anthraquinone dyes investigated. With one of the dyes, optical Freedericksz transition in a planar layer is demonstrated.

MULTIPLE TIME SCALES OPTICAL NONLINEARITIES OF LIQUID CRYSTALS FOR OPTICAL-TERAHERTZ-MICROWAVE APPLICATIONS (Invited Review)

“…The sign of η depends on the particular dye dopants used [54][55][56][57], and its magnitude can be as large as over 10 2 . Accordingly, the magnitude of the nonlinear index coefficients associated with this excited dyemolecules assisted director axis reorientation can be as large as 10 −2 cm 2 /Watt, depending of course on the dye dopant concentration used.…”

Mechanisms of giant optical nonlinearity in light-absorbing liquid crystals: a brief primer

“…The effects were in all respects similar to those that had been observed in transparent materials, but they were so strong that could be easily induced by means of a He-Ne laser of few milliwatts (therefore they were characteristically colored "red" instead of the usual "green" of the Argon laser light, as shown in the following figure). Some clever experiments performed in the following years by Jánossy and coworkers demonstrated beyond any doubt that the nonlinearity was still orientational and not for example "trivially" thermal (see section 5) [13,14,15]. We recall here some of the main experimental evidence: (i) different dyes with the same absorption coefficient give rise to completely different nonlinear effects, contrary to what would be expected for thermal effects; (ii) the angular dependence of the nonlinearity was that expected for the orientational response; (iii) the relaxation time was of the right order of magnitude for an orientational response; (iv) more exotic dynamical effects occurring when the light is circularly polarized were also found to be identical to those observed in transparent materials, except for a two-orders of magnitude reduced intensity.…”

“…(ii) Depending on the specific dye employed, the torque can be also reversed in sign, that is one may have η < 0; in such cases the director n will tend to be reoriented perpendicular to the electric field, instead of parallel [15,16].…”

Reversible Photoinduced Anisotropy of Azoxybenzenes in Nematic Liquid Crystal Phase and in Solid Polymer Solutions

“…В этом случае нелинейно-оптические явления могут проявляться как через нагрев слоя или фотохимических изменений дипольных моментов оптических переходов и поляризуемостей самих ЖК-молекул или примесных молекул, так и через влияние оптически возбужденных состояний моле-кул на структуру ЖК [7][8][9][10][11].…”