Debye-diffraction-based concentric energy analysis on two-photon photoluminescence imaging of gold nanorods under radial polarization illumination

Gold nanorods have been identified to be useful contrast agents as they exhibit pronounced two-photon photoluminescence under laser illumination of appropriate intensity and polarization configurations. In this paper, the two-photon photoluminescence imaging of three-dimensionally randomly oriented gold nanorods under linear and radial polarization illumination is investigated through a concentric energy analysis based on the Debye diffraction theory. Consequently, the effect of the numerical aperture and the apodization function of an objective on the polarization distribution in the focal region can be analyzed to form an important part in the understanding on the efficient excitation of gold nanorods. It is demonstrated that the radially polarized beam is an effective laser mode in generating strong two-photon imaging of nanorods in the presence of objectives with high numerical aperture and large annular obstruction sizes.