Abstract
Nonlinear optics deals with phenomena where “light controls light”; e.g., there is mediation by an intensity-dependent medium through which light propagates. This field has attracted much attention for its immense potential in applications dependent on nonlinear processes, such as frequency conversion, multiple-photon absorption, self-phase modulation, and so on. However, such nonlinearities are typically only observed at very high light intensities and thus they require costly lasers. Here, we report on a self-focusing effect induced with a 1 mW handheld laser pointer. We prepared polymer-stabilized dye-doped liquid crystals, in which the molecular director orientation gradually changes from homeotropic at one surface to homogeneous at the other. This is referred to as hybrid alignment. In such films, the threshold intensity needed to form diffraction rings was reduced by a factor of 8.5 compared to that in conventional homeotropic cells, which enabled the induction of the self-focusing effect with a laser pointer.
Highlights
Non-treated liquid crystals (LCs) cells exhibit huge optical scattering, which is a problem for photonic applications
We have recently found that oligothiophene (TR5)-doped LCs stabilized by photopolymerization exhibit an unexpectedly low threshold intensity for self-focusing[20]
polymer-stabilized TR5-doped LC (PSLC) are described in the Methods section
Summary
Non-treated LC cells exhibit huge optical scattering, which is a problem for photonic applications. Due to the complicated alignment of hybrid-aligned LC cells, we carefully studied the diffraction ring formation for four different cell placement arrangements (Fig. 3), depending on the surface facing the incident light and the angle between the rubbing direction and the polarization direction of the incident laser beam: (1) homogeneous-90, (2) homogeneous-0, (3) When the light was incident to the sample from the surface with homogeneous LC alignment, no rings were observed when the laser polarization was perpendicular to director orientation (homogeneous-90; Fig. 3a).
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