Pulsed Saturated Absorption Competition Microscopy on Nonbleaching Nanoparticles
Chuankang Li, Yuhang Li, Yubing Han, Zhimin Zhang, Yuzhu Li, Wensheng Wang, Xiang Hao, Cuifang Kuang, Xu Liu
Abstract
Super-resolution optical microscopy is a useful tool to investigate physical and biological characteristics on the sub-100-nanometer scale. Here, we develop pulsed saturated absorption competition (pSAC) microscopy to break the diffraction limit in imaging of a series of nonbleaching nanoparticles. Based on the confocal scheme, the input laser beam is divided into doughnut-shaped saturated pulse and Gaussian time-modulated pulse. By adjusting the time sequential of the two pulses, the doughnut-shaped beam transiently saturates the excited-state absorption in the periphery of the focal volume, immediately followed by the Gaussian readout beam which mainly excites fluorophores at the focal center. Through the inhibition of the saturation pulse that confines the fluorescence emission to the central subregion, lock-in detection scheme is utilized to select the characteristic fluorescence signals. We numerically and experimentally demonstrate the resolving capacity of pSAC in imaging biological specimens and subdiffraction resolutions as high as λ/13 and λ/12 are reached in nonfluorescence and fluorescence observation, respectively. The experimental results also show that, compared with stimulated emission depletion (STED) microscopy, pSAC is beneficial to achieve background-suppressed imaging when considering lower-power and fluorescent dye selection.