Anomalous Optical Freedericksz Transition in an Absorbing Liquid Crystal

Fast liquid-crystal elastomer swims into the dark

“…Liquid crystals can also be reoriented by light, with the required intensity dramatically reduced in dye -doped samples 12 . This anomalous reduction in the threshold intensity, the so-called Janossy effect, can be understood in terms of a Brownian ratchet mechanism, where the dye molecules in the nematic field are rotors of light-driven Brownian motors 13 .…”

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

“…In 1990, Istvan Jánossy and his colleagues published a paper reporting the unexpected observation of large nonlinear effects in nematic liquid crystals doped with small amounts (below 1%) of certain dichroic organic dyes [12]. 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).…”

Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene

“…This assumption was confirmed by direct evaluation of optical nonlinearity in self-diffraction ring measurements. 15,16,39 The following experiments were carried out on PSLC cells treated with silane coupler concentrations above 0.003 wt% because these concentrations yielded a uniform homeotropic orientation. Effect of surface treatment on molecular reorientation K Usui et al…”

“…In 1990, Jánossy et al 15 first reported that the threshold light intensity for photoinduced molecular reorientation greatly decreases in an LC doped with a small amount of anthraquinone dye. 27 In this system, the torque to rotate LCs is caused by an optical field and is enhanced by the molecular polarizability of photoexcited dyes.…”

“…[8][9][10][11][12][13][14] In contrast, a photophysical process exploits the nonlinear optical (NLO) effects of an LC. 7,15 When a homeotropic LC is vertically irradiated with linearly polarized light, the interaction between the optical field and the LC molecules generates a torque to rotate the molecular director along the polarization direction, leading to homogeneous (in-plane) orientation. On the other hand, rotation of the molecular director is disturbed both by the interaction between LCs and the glass substrate surface, a process which is also called surface anchoring, and by bulk elasticity.…”