Contd...

provided that the distance is much larger than the particle diameter, i.e. the observer is located in the far-field relative to the particle. In the above expression, is a maximum when is parallel to . For a He-Ne laser MHz /(m/s). In applications, the scattering configuration used is based on convenience and a typical value of is 0.4 MHz/(m/s). The forward and backward scatter configurations are marked (a) and (b) in Figure 3.4 . The latter has the disadvantage of low scattered light intensity but is easily compensated because of the compactness achieved by integrating the source and the receiver optics.

Figure 3.3: Schematic Drawing of Doppler Effect.