Fluctuations of a homeotropically aligned nematic liquid crystal in the presence of an applied voltage

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We determined the refractive-index structure-factor Sₙ(k) from shadowgraphs of fluctuations in a layer of a homeotropically aligned nematic liquid crystal with negative dielectric anisotropy in the presence of an ac voltage of amplitude V₀ applied orthogonal to the layer. Sₙ(k) had rotational symmetry. Its integral P(V₀) and amplitude B(V₀) increased smoothly through the Fréedericksz transition at V₀ = VF. Its inverse width ξ(V₀) and its relaxation rate Γ₀(V₀) had cusps but remained finite at VF. The results are inconsistent with the critical mode at a second-order phase transition.