Determination of refraction index

Determination of the refraction index is required for accurate determination of particle size and distribution – especially for small particles. As one of the few companies in the world, Particle Analytical offers determination of the refraction index of your compound.


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The refraction index (or index of refraction) n of a substance (optical medium) is a number that describes how light, or any other radiation, propagates through that medium. The absorption part describes the amount of light being absorbed by the particle.

In order to make accurate particle size and distribution determination, especially of small particle sizes, it is necessary to know the refraction index of the compound.  The refraction index is determined by laser diffraction, and is not as such a separate method.

For laser diffraction two optical models are generally used, Fraunhofer and Mie:

refrac II

refrac I

To use the Mie theory it is necessary to know the value of refraction index and absorption. If these values are not known, it is essentially “just guessing” and this can have significant effect on the result.

Refractive index is often assumed to be 1.3 to 2.1 for organic material. Most often default values are used in calculation of particle sizes. If these values are not justified it might lead to wrong interpretation of the results.

Please contact us if you want to determine the refraction index of your compound.