Layout of PDA-Systems

Transparent particles may be distinguished between those having a refractive index larger or smaller than the surrounding medium. Liquid droplets or glass beads in air have a relative refractive index m which is larger than unity, typically in the range 1.3 to 1.5, and water droplets in oil or bubbles in liquid have a relative refractive index below unity. 

Reflected light covers the entire angular range for refractive index ratios below and above unity. However, a distinct minimum is found for parallel polarized light at the so-called Brewster s angle which is given for a sphere by  

The Brewster s angle decreases with increasing refractive index ratio. 

First order refraction is concentrated in the forward scattering range and extends up to the critical angle which is given for different relative refractive indices m = np/nm as follows  

The critical angle increases with increasing relative refractive index (m 1) and first order refraction becomes dominant over reflection over a wider angular 

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