${\mathrm{N}\mathrm{A}}_{O}$ and ${\mathrm{N}\mathrm{A}}_{\mathit{\text{OI}}}$ | (Outer) and inner numerical
aperture of the objective lens |

${\mathrm{N}\mathrm{A}}_{C}$ and ${\mathrm{N}\mathrm{A}}_{\mathit{\text{CI}}}$ | (Outer) and inner numerical
aperture of the condenser lens |

$n(\mathit{r})$ | 3D refractive index
distribution of the tested object |

${n}_{0}$ | Refractive index of the
immersion material of the objective |

${n}_{\mathrm{o}\mathrm{b}}$ | Average refractive index of
the object (and surrounding RI-matching material) |

$\lambda $ | Wavelength of the illumination
light |

${\rho}_{{}_{O}}$ and ${\rho}_{{}_{OI}}$ | (Outer) and inner objective NA
normalized by $2\pi \phantom{\rule{negativethinmathspace}{0ex}}{n}_{0}/\lambda $ |

${\rho}_{C}$ and ${\rho}_{{}_{CI}}$ | (Outer) and inner condenser NA
normalized by $2\pi \phantom{\rule{negativethinmathspace}{0ex}}{n}_{0}/\lambda $ |

$O(k)$ | Function that defines the
intensity distribution of light collected by the
objective |

$S(k)$ | Function that defines the
intensity distribution of source (incident) light |

$\sigma $ | Gaussian illumination width
coefficient |

$({k}_{x},{k}_{y},{k}_{z})$ | Normalized source wave vector
space, ${k}_{y}=(1-{k}_{x}^{2}-{k}_{z}^{2}{)}^{1/2}$ |

${\overline{\mathit{\rho}}}_{S}$ and ${\mathit{\rho}}_{S}$ | Source wave vector and its
normalized version by dividing by $2\pi \phantom{\rule{negativethinmathspace}{0ex}}{n}_{0}/\lambda $ |

${\overline{\mathit{\rho}}}_{D}$ and ${\mathit{\rho}}_{D}$ | Diffracted wave vector and its
normalized version by dividing by $2\pi \phantom{\rule{negativethinmathspace}{0ex}}{n}_{0}/\lambda $ |

$\overline{\mathit{K}}$ and $\mathit{K}$ | grating vector in the object
and its normalized version by dividing by $2\pi \phantom{\rule{negativethinmathspace}{0ex}}{n}_{0}/\lambda $, $\mathit{K}=(\mathit{\eta},\mathit{\mu})$ |

$(\mathit{\eta},\mathit{\mu})$ | normalized object’s
spatial-frequency space |

${\mu}_{x}$ and ${\mu}_{z}$ | normalized lateral spatial
frequency of the object in $x$ and $z$ directions |

$\eta $ | normalized axial spatial
frequency of the object in $y$ direction |

$\mathit{\mu}$ and $\mu $ | normalized lateral spatial
frequency vector and its modulus, $\mathit{\mu}=({\mu}_{x},{\mu}_{z}),\mu =|\mathit{\mu}|$ |

$\mathit{k}$ and $k$ | normalized lateral wave vector
of the source light and its modulus, $\mathit{k}=({k}_{x},\phantom{\rule{thickmathspace}{0ex}}{k}_{z}),\phantom{\rule{thickmathspace}{0ex}}k=|\mathit{k}|$ |

${\mathit{k}}^{\mathrm{\prime}}$ | normalized shifted lateral
wave vector of the source light, ${\mathit{k}}^{\mathrm{\prime}}=\mathit{k}+\mathit{\mu}/2$ |

${\eta}_{\mathrm{s}\mathrm{e}\mathrm{l}}$ and ${\mu}_{\mathrm{s}\mathrm{e}\mathrm{l}}$ | selected detectable normalized
axial- and lateral-spatial frequency of the
object |

${\mathit{T}}_{3D}(\eta ,\mu )$ | 3D phase optical transfer
function (POTF) |

${\mathit{T}}_{2D}(\eta ,\mu )$ | 2D phase optical transfer
function (POTF), which indicates the axially symmetric ${T}_{3D}(\eta ,\mathit{\mu})$ |

${\mathit{T}}_{D}(\eta ,\mu )$ | diffracted-light-ellipse
integral |

${\mathit{T}}_{S}(\eta ,\mu )$ | source-light-ellipse
integral |

${l}_{D}$ and ${w}_{D}$ | integration limit and
integrand for calculating ${T}_{D}(\eta ,\phantom{\rule{thickmathspace}{0ex}}\mu )$ |

${l}_{S}$ and ${w}_{S}$ | integration limit and
integrand for calculating ${T}_{S}(\eta ,\phantom{\rule{thickmathspace}{0ex}}\mu )$ |