Leaky annular pupil for improved lateral resolution in confocal fluorescence microscopy

Imaging properties of an optical system may be modified by the introduction of spatial filters at the entrance and exit pupils. A classic example of this is the annular pupil, which is known to improve lateral resolution at the expense of depth discrimination. In confocal fluorescence microscopy, previous studies have shown that a configuration with an annular pupil in the excitation path and ca circular pupil in the emission path offer little improvement. We show here that a more favorable situation results if the annular excitation pupil is design with a partially transmissive central obstruction. Our simulations show that the radii and leakage of the annulus may be adjusted to improve the point spread function's lateral resolution by 13 percent and with not degradation of the Z-axis full width at half-maximum. A slightly different pupil is shown to improve the lateral resolution by 10 percent and the Z-axis response by 5 percent.