Educational Objectives

  • Doppler Shift
  • Beam Interference
  • Scattering of Light
  • Velocimetry
  • Particle Size
  • Fourier Transformation
  • Modulation Depth
  • Beam Intersection Angle

The working principle of a Laser Doppler Anemometer (LDA) is demonstrated. Two coherent laser beams cross at the measuring spot at which a rotating acrylic disc with small distortions is placed. Distortions passing the beams’ cross point generate scattered light. The frequency of this scattered light is up- and downward Doppler shifted causing a low frequency signal beating. This beating is proportional to the velocity of the distortions in the measuring spot. Scattered light is collected by a lens and focused onto a photo detector. By fast Fourier transformation the beating frequency is determined and the velocity of the particles can be deduced. This velocity, definded by the provided controller, can be compared to the rotation velocity of the disc.

Order No. 4900-9-1350