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Mie theory (also known as Lorenz-Mie theory or Lorenz-Mie-Debye theory) describes the analytic solution to Maxwell’s equations for scattering of light from spherical particles. The theory allows the size of the particle to be arbitrary, i.e. the solution is applicable to all ratios for the sphere radius to the wavelength. As this ratio becomes small (<< 1), the Mie model approaches the familiar results of Rayleigh scattering.

As described in the literature¹, Mie theory is important for modeling atmospheric scattering in haze and clouds. The model also can be used to describe the appearance of common materials such as milk, latex paint, and biological tissue.

The Mie model has been implemented in ZEMAX as a bulk scattering distribution in non-sequential mode. The computation is based on the results provided in Chapter 4 and Appendix A of the text by Bohren & Huffman². A description of the model inputs is given on the next page of this article. An example of using the Mie code to model atmospheric scattering is then provided.