Optical nonlinearities induced by laser radiation in some fatty acids from the biological membrane

In this paper, we present a study of pure arachidonic acid, arachidic acid, other fatty acids (FA) and mixtures with cholesterol (Ch) in different ratio of compounds, having smectic C liquid crystal (LC) properties. Very thin systems (`membranes') of FA and mixtures, manufactured by us, were subjected to some electrical measurements, that show a new distribution, induced by Ch, of the space charge in the system. The FA and mixtures' samples were also sandwiched between two glass plates of transparent SnO 2 electrodes and studied under dc and ac electric fields. The hysteresis curves of the current versus the applied voltage exhibited a nonlinear dielectric feature and a negative resistance. We studied the change of the fundamental IR and second harmonic pulsed beam of a Nd 3+ glass laser, in the time domain, after passing through our samples; the optical output power of a He-Ne laser beam ((lambda) equals 6328 angstroms, P max equals 20 mW), from the LC cells situated between parallel and crossed polarizers was registered. A nonlinear optical behavior of the samples and some memory effects were emphasized. Also a correlation between the electric and optical nonlinearity of the samples seems to be possible.