The Phase-Doppler-Difference-Method,a New-Laser-Doppler Technique for Simultaneous Size and Velocity Measurements. Part 2: Optical particle characteristics as a base for the new diagnostic technique

Simultaneous size and velocity measurements can be obtained by using photodetector positions of different off-axis-angles. But not for all of these positions one receives unambiguous results for the correlation between the phase difference and the particle diameter. This can be clearly demonstrated by the plots of the numerical calculations of the complete Mie's scattering equations. These plots show that for transparent particles which exceed the continuous phase in density at special off-axis-angles the situation of light refraction changes into a situation of additional light reflection or vice versa. On the other hand for transparent particles which are less dense compared with the continuous phase and for totally absorbing materials these plots confirm the simplified equations for reckoning the particle diameter by the laws of geometrical optics. The good agreement between these results can also be verified for the backscatter mode for measurements of metallic spheres with an imaginary refractive index.