Fig. 2: Formation of the virtual image and relationship between the photonic nanojet and the projected virtual image plane.
From: Microsphere-assisted, nanospot, non-destructive metrology for semiconductor devices
a Simulated photonic nanojet effect (indicated by the red arrow) by finite-difference time-domain (FDTD) method. b Diagram combining ray optics and FDTD simulation. (\(\overline{AB}\): sample. \(\overline{A\text{'}B\text{'}}\): virtual image. \(f\): photonic nanojet as a front focal point from FDTD. \(f\text{'}\): back focal point. \(T\): microsphere regarded as a thin lens.). c Geometric relationship between the microsphere, sample, and virtual image. \({D}_{{\rm{v}}}\): distance between the virtual image plane and sample. \(({D}_{{\rm{v}}} > 0)\) \({D}_{{\rm{s}}}\): distance between the center of the microsphere and sample. \(({D}_{{\rm{s}}} > 0)\) \({D}_{{\rm{f}}}\): distance between the microsphere and photonic nanojet, obtained by FDTD simulation. \(({D}_{{\rm{f}}} > 0)\) \({w}_{{\rm{d}}}\): distance between the bottom of the microsphere and sample. r: radius of the microsphere. (\({w}_{{\rm{d}}}\ge 0\)). \({Z}_{{\rm{v}}}\): axial position of virtual image. \(({Z}_{{\rm{v}}}=0-{D}_{{\rm{v}}})\).
