Photon Density Wave Spectroscopy

We use intensity modulated laser sources throughout the visible and near infrared spectral range with modulation frequencies from 10 MHz well beyond 1 GHz to generate Photon Density Waves in strongly light scattering materials.

Detection and analysis of PDWs in terms of amplitude and phase with respect to modulation frequency and source-detector distance allow for the precise determination of fundamental optical properties of the material under investigation, namely the absorption and reduced scatttering coefficients. Whereas the first provides access to chemical concentrations, the latter allows for the determination of concentrations or particle and droplet sizes of the dispersed phase without any dilution or calibration.

The analysis is based on radiation transport theory, Mie theorie and several approaches concerning dependent scattering. Don't worry - we know about the details!
  • Intrinsically safe electronics-free, fibre-optics only probe for installations in critical environments (e.g. ATEX)
  • Laser power < 15 mW
  • Typical probe materials: stainless steel, glass, PTFE. Customer specific development possible
  • Probe diameter depends on application. Typical range is 15 - 25 mm
  • Time resolution: approx. 2 per minute
  • Size range: approx. 50 nm - 500 µm (diameter)

Highly turbid liquid dispersions can by analyzed (imagine a glass of milk). Typically we investigate liquid suspensions or emulsions with a content of particles or droplets in between 0.1 % to more then 50 %. In contrast to many other technologies, PDW Spectroscopy is not limited by too strong light scattering. In more than ten years academic research we never received a sample which needed dilution!

See our list of scientific contributions for more theoretical background and examples of investigated materials and processes (Applications).