A new method of short-coherence-interferometry in human skin (in vivo) and in solid volume scatterers

We adapted a method, the ''coherence radar'', that was originally developed for the precise measurement of surface topology, to measure bulk properties within strongly scattering media. The sensor is based on short-coherence-interferometry. It enables the two-dimensional observation of light propagation in scattering media with a high temporal resolution (<100 fs). The measurements are carried out by observing photons that traveled from an entrance focus through the bulk of the sample, and back to the surface. The source of information is the speckle contrast. One important result is that during the propagation a sharp photon horizon evolves. This photon horizon can be used for the detection of inhomogeneities in the scattering properties. In solid samples we measured absorbing obstacles with a depth of 320 mu m and a depth uncertainty of <5%. The measuring time is about 30 seconds. The observation of the photon horizon can also be realized in ''life'' volume scatterers with moving scattering particles. First in vivo measurements of human skin have been successful.