ANNULAR APERTURE 2-PHOTON EXCITATION MICROSCOPY

We investigate the effect of annular apertures in two-photon excitatio n confocal and non-confocal microscopy. In a theoretical study, we sho w that the use of annular apertures in two-photon excitation microscop y leads to resolution increase without diffraction fringes. We determi ne experimentally the axial resolution of annular aperture confocal an d non-confocal two-photon excitation microscopes and compare it with t hat of the standard two-photon excitation contrasts. Images of fluores cence beads obtained with a transmission annular aperture two-photon e xcitation microscope demonstrate the applicability of annular aperture s for enlarging the focal depth in high resolution two-photon excitati on imaging.