4Pi microscopy of type A with 1-photon excitation in biological fluorescence imaging

We demonstrate that oil immersion lenses with a semi-aperture angle >/= 74 degrees enable 4Pi confocal fluorescence microscopy of type A with 1 photon excitation. The axial sidelobes amount to < 50 % of the main diffraction maximum, implying that lobe induced artifacts can be removed from the image data. The advancement reported herein enables a relative inexpensive implementation of 4Pi microscopy, providing axially superresolved 3D-imaging in transparent samples. As an example, we show dual-color 4Pi images of double stained Golgi stacks in a mammalian cell with 110 nm axial resolution. The resolution can be further enhanced to values slightly below 100 nm by image deconvolution.