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DY: Fachverband Dynamik und Statistische Physik

DY 6: Poster Session I

DY 6.54: Poster

Montag, 22. März 2010, 16:00–18:00, Poster B2

The Talbot effect observed in a liquid crystal convection experiment — •Stephan Messlinger, Wolfgang Schöpf, Ingo Rehberg, and Werner Pesch — Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth

As first discovered by Talbot [1], light with a wavelength λ passing through any diffraction grating with wavelength Λ periodically reproduces images of the grating in regular distances z_T = Λ²/λ from the original plane. In this work, we describe the Talbot effect as observed with electroconvection patterns in liquid crystals. Electroconvection occurs when an alternating electric voltage of sufficient strength is applied perpendicularly to a thin liquid crystal layer [2]. The arising flow structures involve periodic modulations of the director field and hence of the refractive index in the layer plane. Thus, the layer acts as a specific amplitude and phase grating tunable by the frequency of the applied voltage in the range of Λ=5...50 µm. As a result, z_T varies from 0.1 to 10 mm, which is conveniently accessible in standard optical setups. We present a detailed comparison to recent theoretical analyses based on a wave optics approach in the limit of small λ/Λ [3]. This method presents a considerable improvement of the traditional treatment of shadowgraphy in the framework of geometrical optics [4].
[1] H. F. Talbot, Philos. Mag. 9, 401 (1836); L. Rayleigh, Philos. Mag. 11, 196 (1881). [2] A. Buka and L. Kramer, Pattern Formation in Liquid Crystals, Springer, 1996. [3] S. P. Trainoff and D. S. Cannell, Phys. Fluids 14, 1340 (2002). [4] S. Rasenat et al., Exp. Fluids 7, 412 (1989).