Fringe mode reflectance laser Doppler microscope system

A reflectance fringe mode Laser Doppler microscope anemometer (LDMA) has been designed and tested. A novel beam splitter permits adjustment of the direction and separation of the two laser beams which form the fringe sensing volume, and furnishes the control needed to compensate for chromatic aberration and variation in optical quality. Tests conducted in a narrow 28:1 aspect rectangular flow channel filled with water showed close agreement between the predicted and measured velocity profiles. Velocity measurements, made alternately in the reflectance and transmittance modes using the same sensing volume in the channel, revealed deviations between the modes of less than 1.1% for water and 2.3% for whole blood. The deviation for the in vivo experiment was better than 2.8%. Velocity profiles were measured alternately in the same sensing volume, (dimensions were 10 x 12 microns) by reflectance and transmittance LDMA in 40 hamster cheek-pouch arterioles, ranging from 65 to 140 microns in diameter. These showed close agreement throughout the range of measured vessels. Reflectance LDMA makes non-invasive, high resolution velocity measurements in the range of 0.03 to 40 cm/s possible in small blood vessels near the surface of opaque organs and tissues. The accuracy and reproducibility of the readings were calculated to be better than 1.1%. Reflectance fringe mode LDMA greatly extends the applicability of LDMA because sites where transmittance LDMA can be applied are limited.