Instrumentation and Measurement Physics(DIMP)
Physique des instruments et mesures (DPIM)

Claude BOCCARA
École Supérieure de physique et chimie industrielles, Paris, France

Optical Imaging in turbid media: New Developments

The use of light to generate an imaging process able to reveal in-depth structures and to quantify them in terms of geometrical (size, position) and optical (absorption, scattering) properties is a new goal for a larger and larger community of physicists. We will recall the main approaches which have been used to overcome the strong loss of the photons directional memory in highly scattering media and their limitations in terms of depth and resolution:

  • Optical coherence tomography or microscopy which selects ballistic photons through an interferometric detection but can be perturbed by multiscattered ones.
  • Time and frequency methods for detecting the first photons emerging from the structure by using fast detectors or optical gates.
  • DC or quasi DC approaches in which the source-detector symmetry plays an important role in revealing local changes in optical properties.
  • Opto-acoustics (often called Photoacoustics) where a locally absorbed laser pulse generates an acoustic signal whose position and depth can be localized by an array of piezoelectric detectors.
  • Acousto-Optics where a localized ultrasonic field modulates the speckle distribution, coupling light and sound in a very different way than the preceding technique.

    We will particularly describe in more detail the techniques used in our laboratory which take advantage of multiple detectors such as CCD sensors working in parallel for faster acquisition times or better signal-to-noise ratios.