In situ diagnostics of the crystalline nature of single organic nanocrystals by nonlinear microscopy.

We elucidate the crystalline nature and the three-dimensionalorientation of isolated organic nanocrystals embedded in a sol-gelmatrix, using a polarized nonlinear microscopy technique thatcombines two-photon fluorescence and second harmonic generation.This technique allows the distinction between mono-crystallinestructures and nano-scale poly-crystalline aggregates responsiblefor incoherent second harmonic signals.