Diffraction gratings were studied in cells of the homogeneously aligned liquid-crystal E7 doped with multiwall carbon nanotubes. These phase gratings were induced by interference modulation of two coherent optical beams, in conjunction with an applied dc field that was perpendicular to the unperturbed director axis. Self-diffraction was observed at all angles of incidence of the writing beams, including normal incidence. A superior nonlinear-index coefficient of 5×10-2cm2/W was obtained after passage of a 44-mW/cm2 beam through a film with a grating constant of 18 μm under an external voltage of 15 V. The observed phenomenon depends strongly on the applied dc field, and the memory effect in a nematic film depends strongly on the grating constant.
© 2001 Optical Society of America
(050.1950) Diffraction and gratings : Diffraction gratings
(160.3710) Materials : Liquid crystals
(160.5320) Materials : Photorefractive materials
(190.7070) Nonlinear optics : Two-wave mixing
Wei Lee and Chi-Shen Chiu, "Observation of self-diffraction by gratings in nematic liquid crystals doped with carbon nanotubes," Opt. Lett. 26, 521-523 (2001)