Effect of absorption on visibility profiles or circularly polarized backscattered laser beam [particle size measurement]

By use of a method based on the laser Doppler anemometry technique and Mie scattering theory, the visibility for a circularly polarized backscattered laser beam is derived and computed. The effect of absorption on the visibility profiles is analyzed. This analysis is made for a fixed real part of the index of refraction of the particles (1.43) and various values of the imaginary part of the index of refraction (5.10^-3, 8.10^-3, 10^-2, 10^-1). It is shown that the technique considered is suitable for particle sizing only when the imaginary part of the index of refraction of the particles is less than or equal to 5×10^-3 . For values greater than 5×10^-3 a nonmonotonic relationship exists between the visibility and the size parameter; therefore, the visibility technique in this case is not feasible for particle sizing