Fig. 2

PSFs modulated by different levels of spherical aberrations. a With different levels of the primary spherical aberrations (Zernike coefficient set to 0, 5 and 10, respectively) appended at the pupil plane, a sub-diffraction-limited light source located at the depth of 50 μm in object space generates discrete spatial PSFs at the image plane. Although additional phases change the spatial PSF intensity profile, it is difficult to directly quantify the effect of this change on DOF. b Based on the wave optical theory, we simulated the phase-space PSFs of a 13 × 13 SAsLFM system with a 20 × /0.5NA objective. The xz-MIPs of typical sub-aperture PSFs with different levels of spherical aberration phases added to the pupil plane are shown on the top. The focal position of the central component with angular coordinate (7, 7) is referred to as the native focal plane (depth = 0). Yellow dashed lines mark the focus position of each sub-aperture element, illustrating that the displacements between different components rise with the increase of spherical aberration. The curves on the bottom show the Gaussian fittings of the normalized light intensity distributions of sub-aperture PSFs along the z-axis. Scale bars: 20 μm (a) and 100 μm (b)