本文提出了一种利用多光子非线性效应的多光子结构光照明超分辨显微成像（multiphoton-structured illumination microscopy, mP-SIM）技术，可实现比线性SIM 更高的成像分辨率。通过扫描正弦结构的照明光激发样本产生多光子荧光信号或谐波信号，从而利用由光学非线性效应产生的非正弦结构信号光的谐波来提高分辨率。本文提出了mP-SIM 理论以重建系统的超分辨图像。如果考虑多光子非线性效应的所有高阶谐波（阶数足够高，即m足够大），则mP-SIM 在理论上可实现无限分辨率。通过实验证实了双光子荧光（2P）-SIM 和二次谐波产生（second harmonic generation, SHG）-SIM 分别可实现86 nm 和72 nm的横向分辨率。对细胞内染色F-肌动蛋白和小鼠尾腱胶原纤维成像，进一步验证了mP-SIM 的超分辨成像能力。该方法不但适用于多光子荧光超分辨显微成像，而且适用于非标记的如SHG等超分辨显微成像；重要的是，该方法不需要特定的荧光团或高功率激发光，可直接用于商用mP显微系统来实现超分辨成像。

We describe a multiphoton (mP)-structured illumination microscopy (SIM) technique, which demonstrates substantial improvement in image resolution compared with linear SIM due to the nonlinear response of fluorescence. This nonlinear response is caused by the effect of nonsinusoidal structured illumination created by scanning a sinusoidally modulated illumination to excite an mP fluorescence signal. The harmonics of the structured fluorescence illumination are utilised to improve resolution. We present an mP-SIM theory for reconstructing the super-resolution image of the system. Theoretically, the resolution of our mP-SIM is unlimited if all the high-order harmonics of the nonlinear response of fluorescence are considered. Experimentally, we demonstrate an 86-nm lateral resolution for 2P-SIM and a 72-nm lateral resolution for second-harmonic-generation (SHG)-SIM. We further demonstrate their application by imaging cells stained with F-actin and collagen fibres in mouse-tail tendon. Our method can be directly used in commercial mP microscopes and requires no specific fluorophores or high-intensity laser.