## Measurement and modelling of the directional scattering of light.

##### Abstract

The quantum nature of light suggests that a photon can interact with matter in two
primary ways. Firstly and perhaps more simply, the photon could be absorbed or
secondly and more complex, it could be scattered into a new direction of propagation.
The scattering process can be thought of as probabilistic, with a statistical distribution
of possible new directions of travel with respect to the original. In the case of interaction
with a small particle of matter, the probability distribution is referred to as the phase
function. In the case of scattering at a surface interface between two bulk materials,
the new direction of travel is distributed according to a function called the Bidirectional
Scattering Distribution Function (BSDF). The BSDF depends on both the direction of
arrival and the direction of scatter (hence bidirectional ), the type of material and the
condition of the surface as well as the wavelength of light.
This work explores a number of areas related to the BSDF, with special attention
to the effects of random light scatter in high performance optical imaging systems such
as space telescopes. These demanding imaging applications require optical components
manufactured to very high standards with respect to shape, smoothness and cleanliness.
This means that random scatter from the surfaces of these optical components must
be controlled to very low levels. The measurement of very weak optical surface scatter
is therefore a problem of particular interest. An interferometric technique has been
proposed here for improving the quality of such measurements. The interference effects
produced in the image by this technique were analysed using Nijboer-Zernike diffraction
theory, leading to a journal publication in Current Applied Physics.