A new optical correlation method is developed for measuring the scattering-particle size distribution function. The method is based on the transformation of the transverse coherence function of the scattered field that forms the scattering-particle images. A device for measuring the scattering-particle size distribution function is proposed that has a response time of about 10 s and can be applied to measure particles with sizes in the range of 3 to 500 μm to within 10%.

Optical correlation method for studying disperse media

A novel optical technique has been developed to measure
particle diameters in multiphase flows with high accuracy. This technique
uses a photodiode array to measure the spatial frequency of the laser
light scattering from a spherical particle located in the measurement volume.
An optimized optical orientation angle is introduced by taking two
scattering mechanisms into consideration, which provides high accuracy
and avoids the measurement-volume effect in sizing large particles. The
performance of the new method was simulated by using the generalized
Lorenz-Mie theory (GLMT) and validated by experiments. The results
show only 2% measurement uncertainty for particle sizes as large as
1200 ?m, which are commonly encountered in gas-solid and bubblywater
multiphase flows. The feasibility of this technique was demonstrated
experimentally.

High-resolution optical particle sizing in an optimized orientation

Bacteria can be said to be small particles in terms of their volume and can be modelled as near-index particles when the average refractive index of their body is close to that of the medium in which they are suspended. This is the case with water based environments whereas the bacterial scatterer is said to be a 'soft particle' and within the Rayleigh-Debye experimental bounds of applicability. However, discrepancies in the past have illustrated insufficiency of geometric assumptions, such as spherical symmetry and simplistic internal structures, as well as the assumption of 'transparency' of the particle. The aim of this work is to generalize the Rayleigh-Debye approximation in order to apply them to a wider class of not necessarily soft scatterers, hence departing from |m --- 1| < 1 to |m --- 1| < 1. We start by establishing a connection between the assumption on the functional expression of the internal field of small particles and that of the function of refractive index, to a generalisation for arbitrary number of layers within a particle of spherical symmetry. Based on the modification of the Rayleigh-Debye approximation (mRDG) with Bessel functions we proceed to formulate an extended version of the arbitrary layers particle for ellipsoidal forms. An application of this n-layer generalised mRDG to the bacterial domain optical properties via simulation, re-establishes the limits of the Rayleigh-Debye approximation as a result of the internal field modification. Finally, we consider the problem of populations of cells modelled as multilayered geometrical structure, consistent with assumptions from bacteriology concerning size distributions and their relationship to statistical frequency functions. The latter problem is examined both when the independent scattering condition is satisfied and when it is violated, leading to increased probability of multiple scattering. Examination of ensembles of inhomogeneous particles was possible due to our generalised approximation which is essentially acting on any infinitesimal volume, within the boundaries of the said layered structured particles, and is the main result of this work. The mathematical treatment presented within this thesis acts as an extension of the known near-index techniques in the theory of scattering for unlimited number of layers and internal distributions of refractive index.

Light scattering models for real-time bacteria characterisation in water based environments

A simple method for determining both the size and the refractive index of spherical transparent particles, being larger in size than the wavelength of illuminating light, is proposed on the theoretical basis of geometrical optics of light scattering. In the theory, the intensity distribution of scattered light at a certain off-axis angle range of a few degrees can be recognized as interference fringes due to two dominant light rays from the particle. The ratio between the interference fringe contrasts of the scattering patterns in parallel and perpendicular polarization components is used to determine the refractive index of particles, whereas the size of particles is evaluated from the fringe pitch. Experiments were performed to confirm the validity of the proposed method. The validity range of the method is also discussed in terms of the light rays scattered into the observation angle. The present method has the advantage that measurements of the absolute intensity are not required to obtain the size and the refractive index of particles.

T Murakami

Papers

Determination of size and refractive index of single spherical particles on the basis of geometrical optics