LDA- Visibility technique for circularly polarized backscattered waves

The visibility for circularly polarized backscattered laser beam is derived and computed. A model is developed to establish a relationship between the visibility and the particle size. The analysis is restricted to spherical absorbing or non-absorbing particles. The effect that the optical parameters, such as beam angular separation (Psi), collecting aperture size(R), and off-axis collecting angle (Phi₀) have on the visibility profiles is examined. It is found that the range of particle sizes over which the visibility technique is applicable increases with decreasing Psi. It is observed that the range of particles for which the technique is applicable is not affected significantly by a change in R (R>4). In addition, in many cases, moving the collecting aperture slightly off-axis improves the quality of the visibility profile for particle sizing. Experimental data are obtained for comparison with the theoretical results for latex particles of known sizes (0.46mum, 0.74 mum, and 0.9 mum, 1.04 mum, 2.02 mum, and 2.91mum). Various visibility values associated with various signals are obtained for each particle. Preliminary results establish that these experimental data follow the same trend as the theoretical results.