Polarization effects in 4Pi microscopy

The effects of different apodization conditions and polarization distributions on imaging in 4Pi microscopy are discussed. Performance parameters are derived that allow the different implementations to be compared. 4Pi microscopy is mainly used because of its superior axial imaging performance, but it is shown that transverse resolution is also improved in the 4Pi geometry, by as much as 25% compared with focusing by a single aplanatic lens. Compared with plane-polarized illumination in a 4Pi aplanatic system, transverse resolution in the 4Pi mode can also be increased by about 18%, using radially polarized illumination, but at the expense of axial resolution. The electric energy density at the focus for a given power input can be increased using electric dipole polarization, which is relevant for atomic physics experiments such as laser trapping and cooling.