A frequency shifting of LDV for blood velocity measurement by a moving wedged glass

Blood flow in the vessel of microcirculation (that is, red blood cells) usually has very slow velocity and a broadening of the frequency spectrum, so that the Doppler frequency signal component overlaps with the pedestal. To solve this problem, a new method is described for the frequency shifting in LDV, that is, a wedged glass is moved across one of the dual incident light beams. To demonstrate that this method is useful for blood flow measurement, the velocity (0.01-0.1 mm/sec) in the small vessels of a caudal fin of a goldfish was measured in vivo.