Bispectral analysis as a probe of quasielastic light scattering intensity fluctuations

摘要

The bispectrum lang;I(0)I(t)I(tgr;)rang; of the intensityIof light scattered quasielastically from a fluid system is shown to be a potentially useful tool for studying complex fluids. Bispectra and time cumulants are calculated, in the time domain, for systems with 1, 2, or many diffusing components, treating separately the consequences of homodyne and heterodyne detection at times 0,t, and tgr;. The experimentally accessible cumulants of the allhyphen;homodyne bispectrum distinguish between systems with exactly two relaxation times and systems with more than two relaxation times. The signalhyphen;tohyphen;noise ratio in a bispectral measurement is shown to be proportional toT1/2,Tbeing the integration time. Clipped scaling of the heterodyne intensityI(t) allows study of the odd powers lang;Verbar;ak(0)aast;k(t)ak(tgr;)Verbar;rang; of the density correlations.