  Self-assembly of organic molecules represents a fascinating playground to
create various liquid crystalline (LC) nanostructures. In this work, we study
layer undulations on micrometer scale in smectic A phases for achiral
compounds, experimentally demonstrated as regular stripe patterns induced by
thermal treatment. Undulations including their anharmonic properties are
evaluated by means of polarimetric imaging and light diffraction experiments in
cells with various thicknesses. The key role in stripe formation is played by
high negative values of the thermal expansion coefficient.
