Resolution enhancement methods of nonlinear microscopy based on structured illumination

Second harmonic generation microscopy (SHGM) plays a significant role in revealing the noncentrosymmetric structures in biomedical researches. Without real-state transition during SHG generation, fluorescence-based superresolution methods cannot be applied to SHGM. To improve the spatial resolution of SHGM, fringe-scanning SHGM (FS-SHGM) system, which combines SHGM with the concept of structured illumination based on a point-scanning geometry, is introduced in this paper. The scanning path of focusing beam is periodically modulated to generate effective illumination pattern on the specimen. Due to the coherence nature of SHG signals, the mathematical model of image formation and reconstruction was established. To demonstrate the system performance, both simulation and experiments were carried out. In experiment, the improvement factor of FS-SHGM can achieve-1.4 in lateral and 1.56 in axial.