Figure 2. Sketch of the membrane-confocal volume set-up for DODS.

The coordinate system and notations are defined. The membrane is in the x–y plane and undergoes small displacements in the z direction. The membrane is positioned such that its average z position, h₀, is at the inflection point of the intensity distribution, I(z). ω₀ and z₀ are the radii of the beam waist in the radial and axial directions, respectively.