AN IMPROVED LASER DOPPLER MICROSCOPE FOR MEASUREMENT OF IN VIVO VELOCITY DISTRIBUTIONS IN THE MICROCIRCULATION

Abstract

This chapter discusses an improved laser Doppler microscope for measurement of in vivo velocity distributions in the microcirculation. In the study described in the chapter, the anesthetized hamster was placed on the microscope stage and an arteriole was selected for measurement of the red blood cell (RBC) velocity distribution. The laser beam was split into two parallel beams of equal intensity and focused from below onto a small region in the mid-plane of the arteriole. The two coherent light beams having plane wave fronts, as would be present in the waist region of two Gaussian light beams, intersect at an angle of 75° (measured). This yields a pattern of plane interference fringes whose fringe spacing is proportional to the wavelength of the incident laser light and inversely proportional to the sine of the half-angle between the two beams. As a RBC passes through the region of interference fringes, it scatters light whose intensity will vary as the light intensity variation within the fringe region. The light intensity variations are detected by the photomultiplier tube (PMT). A dichroic mirror built into the microscope allows scattered laser light to be sent out the side of the microscope to the PMT while transmitting white light from below the arteriole. As a result, the observer can view the intersection fringe pattern of the two laser beams. Misadjustment in the intersection of the incident beams is visible to the observer through the microscope.