Transmission fluctuation spectroscopy

A transmission signal measured on a flowing suspension of particles shows significant fluctuations which contain complete information on particle size and concentration. Details have been published in three parts [90-92]. In parts one and two the basic properties were studied for a beam of uniform intensity. The theoiy was extended in part three to a Gaussian beam with experimental tests to follow. 

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In contrast to absorption spectroscopy the use of a reference is rather difficult. It requires a sample for which absorption and fluorescence spectra both exhibit the same spectral distribution as the probe. This is quite impossible. For this reason in some instrumentation one tries to eliminate fluctuations in the intensity of the light source. The excitation beam is split and a small amount of the intensity of excitation is focused on a photodiode. Nevertheless neither the changes in the optics of the instrumentation nor the variance of the transmission curve with wavelength can be overcome. However there is a way to calibrate the spectral distribution of a fluorimeter in-... 

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