Measurement of refractive index of single microparticles

Knoener, Gregor; Parkin, Simon; Nieminen, Timo A.; Heckenberg, Norman R.; Rubinsztein-Dunlop, Halina

Measurement of refractive index of single microparticles

Authors

Knoener, Gregor

Parkin, Simon

Nieminen, Timo A.

Heckenberg, Norman R.

Rubinsztein-Dunlop, Halina

Description

The refractive index of single microparticles is derived from precise measurement and rigorous modeling of the stiffness of a laser trap. We demonstrate the method for particles of four different materials with diameters from 1.6 to 5.2 microns and achieve an accuracy of better than 1%. The method greatly contributes as a new characterization technique because it works best under conditions (small particle size, polydispersion) where other methods, such as absorption spectroscopy, start to fail. Particles need not be transferred to a particular fluid, which prevents particle degradation or alteration common in index matching techniques. Our results also show that advanced modeling of laser traps accurately reproduces experimental reality.
5 pages, 4 figures