Gaussian beam effects on the photon correlation spectrum from a flowing Brownian motion system

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Abstract
The theory of photon correlation spectroscopy for a flowing system of diffusing particles was extended to include the Gaussian shape properties of an incident light beam. We found that the characteristic time of the coherent translational term caused by the bulk flow of the system was independent of the distance between the scattering volume and the focal point of the incident beam. The flow velocity and beam radius at the focus determined the characteristic time of this term. We also studied the effect of defocusing on the amplitude of the incoherent or number density term of the homodyne-detected intensity autocorrelation function. We verified our results experimentally using a flowing dioctylphthalate aerosol.