A New Technique to Measure Refractive Index with Phase Doppler Anemometry

Abstract

A standard phase-Doppler system was modified to determine the feasibility of refractive index measurements utilizing new optical techniques. With the use of two laser beam systems of different wavelength and a single receiving unit different optical configurations can be explored by varying the scattering, elevation and crossing angles independently for each system. The index of refraction of a droplet can be extracted from the phase-shift ratio of two distinct pairs of apertures. Selecting the proper optical parameters yields a sensitive relationship between phase ratio and refractive index.

For measurements an LDA configuration with two transmitting optics was chosen because of its widespread use and standard components. The two probes were situated 40° relative to each other. This was done to maximize the relationship between the ratio of phase shifts and the refractive index. Tests were conducted on water-glucose mixtures with varying refractive index.