Generation of a 3D isotropic hollow focal spot for single-objective stimulated emission depletion microscopy

Abstract

Single-objective stimulated emission depletion (STED) microscopy has long suffered from resolution anisotropy due to the elongated shape of the hollow STED spot along the optical axis. In this paper, we place a dielectric mirror behind the sample and use spatial light modulators to shape the illumination beam so that both the reflected beam and the incident beam converge to the same point and interfere with each other. By specially setting the reflection property of the dielectric mirror, we show that a 3D isotropic hollow focal spot can be generated while using only one objective lens. When this approach is introduced into STED microscopy, simulated results demonstrate that an axial resolution enhancement of 3.65-fold together with a lateral resolution improvement of 1.14-fold compared with conventional single-objective STED microscopy can be reached.