Lorenz-Mie scattering theory allows to predict the field scattered by spherical objects illuminated by coherent light. By fitting the fringe pattern resulting from the interference of incident and scattered light, it is possible to track and size colloidal particles with a few nanometer precision. Using digital holographic microscopy (DHM) we extend the applications of Lorenz-Mie theory to hollow spherical structures and to extremely high pressure conditions. On the one hand, we geometrically and optically characterize complex colloids as polymer-shelled microbubbles, with high precision, low costs and short acquisition time. These microbubbles are likely to be unique tools for targeted drug delivery and are currently used as contrast agents for sonography. We measured size, shell thickness and refractive index for hundreds of polymeric microbubbles showing that shell thickness displays a large variation that is strongly correlated with its refractive index and thus with its composition. On the other hand we demonstrate that DHM can be used for accurate 3D tracking and sizing of a holographically trapped colloidal probe in a diamond anvil cell (DAC). Polystyrene beads were trapped in water up to Gigapascal pressures while simultaneously recording in-line holograms at 1 KHz frame rate. This technique may potentially provide a new method for spatially resolved pressure measurements inside a DAC.

© 2016 COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Filippo Saglimbeni, Silvio Bianchi, Roberto Di Leonardo, Miles J. Padgett, Graham Gibson, Richard W. Bowman, and Gaio Paradossi, "Lorenz-Mie digital holographic microscopy on complex colloids and at extreme pressure conditions (Conference Presentation)," Proc. SPIE 9718, Quantitative Phase Imaging II, 97182X (Presented at SPIE BiOS: February 18, 2016; Published: 27 April 2016); https://doi.org/10.1117/12.2211039.4848767863001.