## 2010 Nano-Biophotonics Summer School @ UIUC Lecture 4 - Gaussian beam propagation - Elastic light scattering - Dynamic light scattering

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#### Abstract

Often, experiments involve light beams. A light beam can be defined as a distribution of field that fulfills the approximation in Eq. 20,

i.e. is characterized by a dominant wave vector component, k(z) >> k(x) , k(y) . A beam is, therefore, the spatial equivalent of quasimonochromatic

light, where the field is characterized by a dominant (temporal) frequency component.

A Gaussian beam, such as that delivered by a single (spatial) mode laser, exhibits a field distribution described by a Gaussian

function in the transverse coordinate.

The general goal in light scattering experiments is to infer information about the refractive index distribution n(r) from

measurements on the scattered light, i.e. to solve the inverse problem. In the following, we show that this problem can be solved if we

assume weakly scattering media.

Dynamic light scattering (DLS) studies the properties of inhomogeneous and dynamic media. A generic experimental situation is

illustrated in Fig. 1, where a plane wave scatters on a system of randomly moving particles.

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University of Illinois at Urbana-Champaign, Urbana, IL