Homodyne light scattering

Z c of the intensity fluctuations. In a homodyne light scattering experiment, 7 c is related to the translational diffusion coefficient, Dy, of the particles by the relationship... 

G. G. Fuller, J. M. Rallison, R. L. Schmidt, L. G. Leal, The measurement of velocity gradients in laminar flow by homodyne light-scattering spectroscopy, J. Fluid Mech., 100, 555 (1980). 

Equation (6.29) is the governing equation for the use of homodyne, dynamic light scattering for measurement of velocity gradients. What is left is to specify the shape of the intensity distribution of the incident light within the scattering volume. As an example, if... 

The other geometric consideration is the relative orientation of the scattering vector, q, and an applied field, such as a flow or electric field. For example, as seen in Chapter 6, the use of homodyne dynamic light scattering to measure velocity gradients requires that q be oriented parallel to the component of the velocity of interest. This is simply accomplished by having that velocity component directed parallel to the vector bisecting k(. and k [44],... 

Fig. 1.2.2. Schematic illustration of the various techniques used in light-scattering experiments (a) filter methods (b) homodyne (c) heterodyne.

The term <<5/c(0)<5ic(0> gives the time-dependence of the fluctuations measured by light scattering. In general, for a homodyne experiment... 

Tanaka et al. (1973) have compared the elasticity moduli of 5% and 2.,5% polyacrylamide gels in water, obtained by meaisuring the deformation of their cylindrical samples and by means of dynamic light scattering. The time correlations of scattered light were meeisured on a set of the homodyne spectroscopy of mixing, and the squared correlation function of the field was determined (see Equation 2.3 33). 

Correlation spectroscopy is based on the correlation between the measured frequency spectrum S(co) of the photodetector output and the frequency spectrum I((jo) of the incident light intensity. This light may be the direct radiation of a laser or the light scattered by moving particles, such as molecules, dust particles, or microbes (homodyne spectroscopy). In many cases the direct laser light and the scattered light are superimposed on the photodetector, and the beat spectrum of the coherent superposition is detected (heterodyne spectroscopy) [12.81,12.82]. 

An example of an application of homodyne spectroscopy is the measurement of the size distribution of small particles in the nanometer range that are dispersed in liquids or gases and fly through a laser beam. The intensity 4 of the scattered light depends in a nonlinear way on the size and the refractive index of the particles. For small homogeneous spheres with diameters d, which are small compared to the wavelength (d A), the relation oc d holds. In Fig. 12.25 the measured intensity distribution of laser light scattered by a mixture of latex spheres with d = 22.8 nm and d = 5.7 nm (small squares) is compared with the size distribution obtained from electron microscopy, which can be used for calibration [12.91]. 

G.D.J. Phillies, Suppression of multiple scattering effects in quasielastic light scattering by homodyne cross-correlation techniques. J. Chem. Phys. 74(1), 260-262 (1981a). doi 10.1063/l. 440884... 

G.D.J. Phillies, Experimental demonstration of multiple-scattering suppression in quasielastic-light-scattering spectroscopy by homodyne coincidence techniques. Phys. Rev. A 24(4), 1939-1943 (1981b). doi 10.1103/PhysRevA.24.1939... 

Heterodyne detection method for the coherent detection of laser signals, which superposes the optical signal with a reference beam from a coherent light source (local oscillator) in contrast to homodyne detection, the local oscillator is operated at a slightly different frequency than the optical signal heterodyne measurements allow for velocity measurements via Doppler effect and are employed, e.g., in electrophoretic light scattering. 

Several well-known experimental techniques are employed in laser light scattering. Here we describe the homodyne and heterodyne methods. Both methods use a laser source for incident radiation. Both use a photomultiplier as a detector followed by an autocorrelator for computer analysis. The autocorrelator is defined as... 

Dynamic light scattering, photon correlation spectroscopy, heterodyne/ homodyne method) QELS Electromagnetic wave interaction 0,005-2... 

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