When light hits rough surfaces, small particles or material inhomogenieties, it gets deflected from its
original direction. This effect is called light scattering. It plays a very important role in
research and technology:
Often scattered light is considered as unwanted or straylight, because it deteriorates the image quality
of optical systems, reduces contrast, leads to glare or even to damage of system components.
- The intensity, angular and polarization characteristics of scattered light depend on the
properties of the scattering centers; therefore light scattering is an excellent analysis tool for
non-destructive, contact free material testing, e.g., using laser particle sizers.
- In illumination system design, light scattering is useful for guiding light and for homogenization
of the luminance.
Rough surfaces or surfaces contaminated with particles scatter light and thus become secondary light sources.
The radiance of such a source, relative to the irradiance of the incident light is called BSDF (bi-directional scattering distribution function) gives a complete description of the scattering properties of the surface (if polarization is neglected). Depending on whether the diffusely scattered light gets transmitted or
reflected, the BSDF is also called BTDF (bi-directional transmittance distribution function) or BRDF (bi-directional reflectance distribution function).
In the ideal case, the BSDF is given as a scattering model which has been fitted to measured data.
In some cases, when the scatterers are sufficiently well characterized, the BSDF can also be
calculated from first principles.
- Perform BSDF measurements (in progress)
- Create and evaluate BRDF or BTDF models from measured data
- Compute BSDF models from first principles, e.g., using Mie theory for surface
contamination or Rayleigh Rice theory for surface roughness
- Create effective BSDF models for structured surfaces or (thin) layers of volume scatterers.
- Simulation of optical systems taking into account surface scattering
Volume light scattering
Small particles or other volume inhomogeneities scatter light and lead to turbidity (haze).
Often volume light scattering can be considered as a sequence of scattering from individual
scattering centers and straight propagation between the centers. Consequently, the properties of a volume scattering medium depend on the optical properties of the scattering centers as well as on their spatial distribution.
For modeling the scattering centers, numerous theoretical methods are available, in particular Mie theory, the extended
boundary condition method (EBCM), Discrete Dipole Approximation (FDTD)
or the Finite Different Time Domain method (FDTD). The simulation of the propagation in the volume scattering medium is normally done by Monte Carlo ray-tracing.
- Technological and scientific consulting
- Create scattering models from measurements
- Modeling of the individual scattering centers using various theoretical methods.
- Radiative transport calculations for scattering materials
- Simulation of complete opto-mechanical system, in which volume light scattering plays a role, such as
diffuse light guides, bio-optical systems, atmospheric optics, optical particle sizing.
- Software development based on a rich software library for volume light scattering
Last changed: January 13, 2017 © 2011–2016 Hembach Photonik GmbH