Laser Doppler Velocimetry

  • Laser beams are aligned at the stationary layer in the cell
  • At the crossing point of the beams, Young's interference fringes of known spacing are formed
  • Particles moving through the fringes under the influence of the applied electric field scatter light whose intensity fluctuates with a frequency that is related to the particles velocity
  • Photons detected are input to a digital correlator
  • A frequency spectrum is produced from which the mobility and hence zeta potential are calculated
Measuring particle mobility in the Zetasizer

What about particles with no charge?

  • Particles with no charge will not move in an applied electric field
  • They will not be able to be detected
  • This problem is overcome by making the interference fringes move
  • This is done by using a device called a modulator
What happens if the fringes move but the particles do not?

What happens if the fringes and the particles are moving?

Doppler effect

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