Dresden 2003 – scientific programme
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DY: Dynamik und Statistische Physik
DY 46: Poster
DY 46.89: Poster
Thursday, March 27, 2003, 15:30–18:00, P1
Laser diffraction study of stochastically excited nematic electroconvection — •Thomas John1,2, Ulrich Behn1, and Ralf Stannarius2 — 1Institut für Theoretische Physik, Universität Leipzig — 2Institut für Experimentelle Physik I, Universität Leipzig
Electrically driven convection (EHC) in nematics represents one of the most thoroughly studied spatially extended pattern forming systems. We apply a laser diffraction technique to investigate the wave vectors and time dependent amplitudes of the convection patterns. Analytical calculation of the light propagation through the periodically modulated director field establishes a quantitative relation between the diffraction spot intensities and amplitudes of the director deflection in the convection rolls.
A comparison of different methods for the calculation of the diffraction profiles is given and different levels of approximations are discussed. A rigorous solution of the Maxwell equations for the solution of the problem is still not available. It is shown that for small director deflection angles, the application of Fermat’s principle provides satisfactory results.
We apply the method to a directe measurement of the pattern amplitude near the forward bifurcation of the first instability, and we measure the amplitude fluctuations in stochastically driven EHC. Trajectories of the pattern amplitude under non-deterministic excitation can be recorded with a time resolution better than the characteristic times of the excitation process and director response.
[1] Th. John, U. Behn, and R. Stannarius. Phys. Rev. E, 65 046229 (2002).