Investigation of molecular and protein crystals by three photon polarization resolved microscopy

We implement three photon fluorescence polarization resolved microscopy to optically investigate molecular and protein crystals. The availability of UV transitions using IR pulses allows analyses without fluorescence staining. Polarization resolved studies indicate that high-order symmetry structures can be revealed and that strong fluorescent energy transfer occurs between molecules. We show how this permits identification of a monocrystalline nature for a sample at the subwavelength resolution scale.