Simultaneous observation of molecular tilt and azimuthal angle distributions in spontaneously modulated liquid-crystalline Langmuir monolayers

We carried out the first quantitative measurements of correlated modulation s of molecular tilt and azimuthal angles in two-dimensional smectic-C Langm uir monolayers using simultaneous linear- and circular-polarized reflected light microscopy. For spontaneously formed stripes and higher-order point d efects, the tilt angle varies nearly sinusoidally at twice the spatial freq uency of the azimuthal rotation. The tilt modulation grows as the second po wer of the modulation wave number and leads to a large escaped core for the point defect. Our results can be explained by an extended Landau theory of tilted smectics.