Optical EngineeringNew type of manifestation of the Doppler effect: an application to blood and lymph flow measurements
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Based on theoretical and experimental analyses, it is shown that the spectrum of intensity fluctuations contains a high-frequency peak in the absence of a subsidiary reference wave at nonsmall angles of speckle observation. This phenomenon, interpreted as a new type of manifestation of the Doppler effect, is usual only for the case of strongly focused coherent beam scattering. The possibilities for using the observed effect in the measurements of blood and lymph flows in narrow native capillaries are discussed. The traditional Doppler method using strongly focused Gaussian beam scattering is also considered. It is shown that the frequency position of the Doppler peak in the spectrum of intensity fluctuations is defined not only by the angle of speckle observation but also by the relation between the waist beam diameter and the average size of flow inhomogeneities. This result was experimentally verified. It is concluded that the Doppler method of blood flow measurement using strongly focused Gaussian beam diffraction should be revised.