Electroconvection patterns in smectic films at and above onset

We have studied patterns of electrically driven convective vortices in thin freely suspended films of smectic liquid crystal at and above the onset of convection. We present measurements of the convective amplitude above onset, the spatial variation of the amplitude due to the presence of end walls, and the relaxation of the amplitude following a sudden change in the experimental control parameter. Our experimental results are shown to agree with predictions based on the Ginzburg-Landau equation, and we find values for the dimensionaless length and time scales of the Ginzburg-Landau equation.