Optical spatial intensity profiles for high order autocorrelation in fluorescence spectroscopy.

Interpretation of spatially resolved optical spectroscopies requires knowledge of the optical excitation and collection profiles of the experimental apparatus. This paper describes measurement of the relative norms of the spatial profile of a microscope- and laser-based optical system. The profile is given by the product of the spatial intensity of a focused laser beam and the point collection efficiency of the microscope. Experimental determination of the values of the norms is essential to the use of high order autocorrelation in fluorescence correlation spectroscopy to measure the concentrations and relative fluorescence yields of different fluorescent components (e.g., monomers and oligomers) in a multicomponent solution and also permits evaluation of theoretical models of the optical spatial intensity profile. In addition, the results may have applicability to high order autocorrelation in other optical spectroscopies, to confocal microscopy and to nonlinear optics in general.