DYNAMIC LIGHT-SCATTERING WITH SINGLE-MODE RECEIVERS - PARTIAL HETERODYNING REGIME

A frequent source of errors in dynamic light-scattering experiments is partial heterodyning caused by scattering on large particles or imper fections of the sample cell. With a conventional two-pinhole receiver it is impossible to distinguish its effect from the effects of a finit e detector area and detector nonlinearity. However, an accurate data a nalysis is feasible when a single-mode light receiver is employed. We present formulas for single-mode autocorrelation and cross-correlation functions that include a local oscillator and an incoherent backgroun d of arbitrary strength and take into account detector nonlinearity (e .g., dead time) up to second order. A simple but accurate method for t he determination of the nonlinearity parameters and the effective numb er of receiver modes is also provided. The success of the data-evaluat ion procedure is demonstrated by the measurement of the hydrodynamic r adius of latex in the presence of deliberately added local-oscillator or incoherent-background contributions. (C) 1997 Optical Society of Am erica.