Noninterferometric differential confocal microscopy with 2-nm depth resolution

By utilizing the sharp slopes of the axial response curve of confocal imaging, we demonstrate a differential confocal technique for surface imaging with depth resolution as great as 2 nm. Neither servo feedback loop nor lock-in detection are used, hence measurements can be performed at high speed with long working distance. Because the technique uses no interferometric effects, it offers large open-loop dynamic range and is compatible with fluorescence microscopy.