A liquid-crystal Etch A Sketch

Although liquid crystals are commonly associated with sophisticated, state-of-the-art displays, the standard method for preparing them is decidedly low-tech: Rub two polymer-coated plates with a cloth, then sandwich them around a solution of rod-shaped molecules to form a liquid-filled cell. The rubbing imprints tiny grooves into the plates’ surfaces, and the rod-shaped molecules align parallel to those grooves in what’s known as a nematic liquid crystal phase. Some applications, however, call for more complicated molecular arrangements. To exploit liquid crystals’ birefringence to make tunable lenses and aberration correctors, for instance, one needs to be able to create cells containing multiple liquid-crystal domains of prescribed shape, size, and orientation. Giorgio Mirri, Miha Škarabot , and Igor Muševič of the Jožef Stefan Institute in Ljubljana, Slovenia, have now shown that they can create such domains in an ordinary liquid crystal cell by scanning an IR laser across its surface. As the laser spot sweeps by, the liquid crystal melts and, on cooling, assumes a new orientation that depends on the direction in which the spot was moving. The researchers demonstrated the technique by creating the image of a van shown here. Backlit by polarized light, the various domains can be distinguished by their appearance. The magenta background corresponds to the unaltered, horizontally oriented phase. In the bluish regions (the window and windshield), the orientation was rotated counterclockwise by 45°; in the yellowish regions (the wheels and frame), it was rotated clockwise by the same angle. The technique could prove useful in the fabrication of various optoelectronic devices, including liquid crystal displays. (G. Mirri, M. Škarabot, I. Muševič, Soft Matter, in press .)