High volume confinement in two-photon total-internal- reflection fluorescence correlation spectroscopy

We report results on two-photon total-internal-reflection fluorescence correlation spectroscopy with radially polarized light. The combination of liquid crystal spatial light modulator, providing radial polarization, with ultrafast laser (picosecond Nd:GdVO4 laser) allowed us to take the advantage of nonlinear optical contrast mechanisms to suppress the side-lobe energy specific for radial polarization and reduce the effective excited volume twice compared to one-photon evanescent wave excitation in fluorescence correlation spectroscopy.