Broadband Mie scattering from optically levitated aerosol droplets using a white LED.

We describe a simple and efficient means of using a white LED source to illuminate an optically levitated aerosol droplet to enable study of broadband Mie scattering. The backscattered resonances are imaged through a spectrograph and CCD which show high resolution Mie scattering intensity distributions across a spectral range of 480 to 700 nm. The wide spectral range allows assignment of resonance mode numbers and mode orders using conventional Mie theory calculations. Accurate droplet sizing, within +/- 2 nm, is possible for water-based droplets with radii between 2 microm and 8 microm. We additionally demonstrate that the refractive index dispersion can be determined from a single refractive index value at known wavelength. Finally, morphological droplet dynamics are presented showing non-linear droplet evaporation behaviour at a temporal resolution of 100 milliseconds.