Pulsed laser-induced liquid crystal alignment parallel to the exposure polarization

The alignment of a nematic liquid crystal (LC) parallel to the polarization direction of the laser could be induced by three types of polyimide (PI) f ilms, a PI based on aromatic dianhydride and two PIs on alicyclic dianhydri de, exposed to polarized pulsed laser at 266 nm at high fluence in air. The UV-visible absorption spectra of the PI films showed that a remarkable che mical change occurred after exposure at the high fluence in air. In contras t, in argon atmosphere the PI based on aromatic dianhydride was radiation-r esistant and the exposed PI film could induce alignment of the LC molecules parallel to laser polarization. We estimate that the mechanism of the para llel alignment observed in argon is not the photodegradation but the orient ation of the PI molecules.