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2 May 1997 Coherence effects in laser Doppler blood flowmetry
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In laser doppler blood flowmetry (LDBFM), the flow is derived from the first moment of the power spectrum of the photocurrent. This quantity depends on both the spectral width and the modulation depth of the signal. This modulation depth depends on the amount of speckles on the detector surface. The speckle size is determined by the wavelength, the local wave form and the angular distribution of the incoming light.In theoretical treatments of laser speckle, the distance between the light source and the illuminated screen or detector is often taken much larger than the light source dimensions. In direct contact LDBFM where the detector is placed directly on or close to the skin, such assumptions do not hold, making analytic solutions of the problem impossible. The issue is studied by means of a model experiment. A scattering medium is illuminated by tow beams originating from the same laser, one of which is shifted in frequency. With a detector close to the surface of the medium, beats are observed at the difference frequencies. From the modulation depth of these beats, it is possible to derive the speckle size. The main purpose of this paper is to present this conceptually simple experiment. The first experimental results are shown. Although still of limited quality, they show the potential of the method to study the effects of scattering anisotropy, mean free path length, the detector size and its distance to the tissue.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Wiendelt Steenbergen, Matthijs van Stratum, Frits F. M. de Mul, and Jan Greve "Coherence effects in laser Doppler blood flowmetry", Proc. SPIE 2982, Optical Diagnostics of Biological Fluids and Advanced Techniques in Analytical Cytology, (2 May 1997);

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