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## Nanosphere Optics Lab

Optical properties of nanospheres suspended in water, air, or other solutions

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#### Abstract

Nanosphere Optics Lab uses Mie theory to calculate the absorption, scattering, and extinction spectra of spherical nanoparticles. Calculations for spheres of a constant dielectric, as well as the wavelength dependent dielectric materials gold and silver are possible for a range of particle sizes.

Understanding how light interacts with small particles is necessary for a description of a wide range of physical phenomenon. When electromagnetic radiation is incident on a particle the charges in the material are set in motion. This coupling of the incident field to the charged particles gives rise to absorption, via energy tranfer to the surrounding medium, and scattering, via reradiation of the electromagnetic field.

For objects whose dimensions are much larger than the wavelength of light geometric optics will suffice. However, when the particle size is on the order of the wavelength of light a more complicated approach is necessary. For a solution to this problem we turn to electromagnetic theory in the form of the classical Maxwell's equations. In general, the exact solution of the Maxwell equations for an arbitrary particle is complex. However, we can gain insight into the light-particle interaction by examining the absorption and scattering due to small spherical particles. The formal solution to this problem was first given by Gustav Mie in 1908 and is now known as Mie theory.

The Nanosphere Optics Tool uses Mie theory calculate the absorption, scattering, and extinction, which is the sum of absorption and scattering, for a spherical particle of given radius and dielectric constant. The results of the current simulations are given as extinction factors relative to the expected result from geometric optics.

- Nanosphere Optics Lab is powered by B. T. Draine's modified version of the Mie theory code found in C. F. Bohren, D. R. Huffman "Absorption and Scattering of Light by Small Particles" John Wiley and Sons, Inc., 1983.
- Modified f77 version of Bohren and Huffman's code can be found at B. T. Drain's page:

http://www.astro.princeton.edu/~draine/scattering.html