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Dzakpasu and Axelrod (2004a) show that significant irradiance fluctuations exist in the image plane of an optical microscope that corresponds to an area (volume) in the object plane, which contains randomly moving scattering centers smaller than the microscope resolution (roughly the wavelength of light). In this version of DLS, the sample volume may be so small, that the fluctuations of the number of particles (see ) in that volume may significantly contribute to these irradiance variations. Dzakpasu and Axelrod derive a contribution of the number fluctuations to the irradiance autocorrelation function by assuming the Poisson distribution of the number concentration of particles.
In order observe the irradiance fluctuations, the pixel size in the image plane should not exceed the spatial correlation length, lc, of the dispersion:
| lc = [ λ / (2π) ] (M / NA) | (1) |
where λ is the wavelength of light in the dispersion medium, M is the magnification, and NA is the numerical aperture of the microscope objective. See also DLSM applications.
| CITATION: Jonasz M. 2006. DLS microscopy (DLSM) (www.tpdsci.com/Tpc/DLSM.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 13-Jan-2006 Modified: 07-Sep-2006 Peer-reviewed: PENDING |