Stationary Optical Noise in Planar Nematic Liquid Crystals Near the Fréedericksz Transition

We measure, under stationary conditions, the power spectrum of the transmitted and scattered light intensity in a planar nematic liquid crystal cell as a function of the applied voltage in the neighbourhood of the electrically-induced splay Freedericksz transition. The Freedericksz threshold is independently determined using a standard interferometric technique. The low-frequency noise spectral density of the transmitted light displays a well defined peak at the critical voltage; this feature is instead hidden in the scattering noise. We critically examine the performances of these different experimental techniques and show that noise measurements are an adequate tool to study orientation transitions in nematic liquid crystals.