Effect of polarization, phase and amplitude on depletion focus spot in STED

As Stimulated Emission Depletion (STED) super-resolution microscopy has a lower resolution, this paper explores the effects of multiphysical variables including light polarization, phases and amplitudes on the focal spots, in order to form a ring-shape depletion focus spot with sharper Full Width at Half Maximum (FWHM) and to increase the resolution of the microscopy. According to Richards-Wolf vector theory, the models of depletion focus spots were established under the actions of polarization, phase and amplitude, the focus spot distribution was calculated in different polarization, phase and amplitude conditions and the distribution of effective fluorescent excitation was obtained by optimizing the parameters. The results show that: by using azimuthal polarization light as depletion, the FWHM is better than those of radial or circular ones; modulations of phase and amplitude are able to reduce the FWHM, and the theoretical value of effective fluorescent excitation FWHM is only 13.2 nm after optimization. By using polarization state, phase and amplitude to modulate the depletion focus spot, the FWHM can be reduced and a higher resolution can be obtained, which is more effective than that using only single physical variable. Moreover, the high quality depletion focus spot and super-resolution ability can be obtained with azimuthal polarization light in STED and the resolution can further be optimized by phase or amplitude modulations based on different realities.