We have developed a second harmonic photoacoustic microscopy (SH-PAM) for subdiffraction-limited imaging based on nonlinear thermal diffusion. When a sine-modulated Gaussian temperature field is introduced by a laser beam, the temperature dependence of the thermal diffusivity induces a nonlinear photoacoustic (PA) effect and thus results in the production of second harmonic PA signals. We demonstrate through both simulation and experiment that the second harmonic PA images can be reconstructed with a lateral resolution exceeding that of conventional optical resolution PA microscopy. The feasibility of SH-PAM was verified on phantom samples. Amphioxus zygotes and germinated pollens have been studied by SH-PAM to demonstrate its biomedical imaging capability. This method expands the scope of conventional PA imaging and opens up new possibilities for super-resolution imaging, prefiguring great potential for biological imaging and material inspection.

中文翻译：

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基于非线性热扩散的亚衍射极限二次谐波光声显微镜

我们已经开发了二次谐波光声显微镜（SH-PAM），用于基于非线性热扩散的亚衍射极限成像。当通过激光束引入正弦调制的高斯温度场时，热扩散率的温度依赖性会引起非线性光声（PA）效应，从而导致产生二次谐波PA信号。我们通过仿真和实验证明，二次谐波PA图像可以以超过传统光学分辨率PA显微镜的横向分辨率重建。SH-PAM的可行性已在幻像样品上得到验证。SH-PAM已对两栖合子和发芽的花粉进行了研究，以证明其生物医学成像能力。