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An optical method is introduced for observation of temporally and spatially resolved frames that show how light propagates in diffusely scattering materials. The method permits videos with 100-fs resolution in time to be produced. The method utilizes short-coherence interferometry. The source of information is the speckle contrast. The temporal and spatial evolution of the multiple scattering process is demonstrated for several biological and industrial samples. A major objective of the method is to investigate the conditions for optimum coherence and optimum apertures to achieve high resolution in the short-coherence interferometry. One important result is that during the propagation a sharp photon horizon evolves, which is useful for the morphological analysis of volume scatterers.

A three-dimensional (3D) rewritable optical memory using photochromic material is described for high-density memory. The bits are recorded in a 3D volume of photochromic material. A transformation of the photochromic molecule between two isomers with different absorption spectra can be stimulated by irradiation with appropriate wavelengths. We show that a nondestructive readout of photochromic memory is possible by use of a small difference in the refractive index of the photochromic isomers in the near-IR range. For this purpose a near-IR laser-scan differential phase-contrast microscope is used. Experimental results of 3D recording and nondestructive reading are presented.

The ,,Spectral Radar" is an optical sensor for tomography, working in the Fourier domain, rather than in time domain. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. One important property of optical coherence tomography (OCT) sensors is the dynamic range. We will compare the dynamic range of the spectral radar with standard OCT. The influence of the Fourier transformation on the dynamic range of the Spectral Radar will be discussed. The dinical relevance of the in vivo measurements will be demonstrated.