本文提出了一种基于非线性热扩散效应的光声二次谐波显微SH-PAM成像技术，用于实现亚衍射极限光声成像。生物组织受到强度调制的高斯激光束辐射时，组织吸收光子形成高斯分布的温度场，由于热扩散系数非线性热效应引起的非线性光声PA效应，从而产生光声二次谐波信号。模拟和试验结果均表明，重建后的光声二次谐波成像的横向分辨率超过了传统光学成像分辨率。本文通过仿体样品验证了该方法的可行性，并且对人表层皮肤细胞进行了成像，以证明其对生物样品的成像能力。该方法扩展了传统光声成像的范围，为超分辨成像开辟了新的可能性，为生物医学成像和材料检测提供了新的方法。

This paper presents a second harmonic photoacoustic microscopy (SH-PAM)for subdiffraction-limited imaging based on nonlinear thermal diffusion. When biological tissues are irradiated by intensity modulated Gaussian laser beams, the temperature field of Gauss distribution is formed by absorbing photons in tissues. Considering the nonlinear photoacoustic (PA)effect caused by the nonlinear thermal effect of thermal diffusivity, the second harmonic photoacoustic (SHPA)signal is generated. The simulation and experimental results show that the lateral resolution of reconstructed photoacoustic second harmonic imaging is higher than that of traditional optical imaging. In this paper, the feasibility of this method is verified by bionic samples, and the imaging of human skin epidermal cells is carried out to prove its imaging ability for biological samples. This method expands the range of conventional photoacoustic imaging, opens up new possibilities for super-resolution imaging, and provides great potential for biomedical imaging and material detection.