Three-dimensional fluorescence nanoscopy of single quantum emitters based on the optics of spiral light beams

Far-field superresolution fluorescence microscopy (nanoscopy), awarded the Nobel Prize in Chemistry in 2014, has become one of the most powerful tools in multidisciplinary applications of photonics. In this paper, we discuss the technique of three-dimensional nanoscopy with the detection of transformed fluorescence images of single quantum emitters (using the example of semiconductor colloidal quantum dots, QDs). Nanoscale spatial resolution when reconstructing all three coordinates of single QDs is achieved by the instrumental modification of the point spread function using highly efficient light phase spatial modulators (diffractive optical elements, DOEs). DOE phase distributions, which ensure the formation of two-lobe light fields (with rotation of the intensity distribution during light propagation), were obtained on the basis of the optics of spiral light beams. The question of calculating DOEs that provide the best conversion efficiency of light beams is discussed. Theoretical and experimental analyses of the accuracy of the method were carried out depending on the experimental parameters: QD photoluminescence intensity, signal acquisition time, laser excitation power, and the instrumental function of the microscope objective. It is shown that, for the studied CdSeS/ZnS QDs, the accuracy of determining the coordinates can reach values of $\sim 10$ nm at exposure times of $\sim 100$ ms.