光诱导力显微镜中的光致力分析

当入射光照到光诱导力显微镜的悬臂尖端时，在共振频率下激发尖端的偶极子响应。当尖端靠近介质基底或者样品表面时，产生了光致力。因此，PiFM体系中的光致力主要由光致偶极子-偶极子相互作用力主导。如图1所示，将尖端偶极子记为Pt，极化率为αt,图像偶极子记为pt'，极化率为αt'。假设主导极化方向为z，则沿z轴方向产生的光致力可以表示为：

When the incident light illuminates the cantilever tip of the photothermal force microscope, the dipole response of the tip is excited at the resonance frequency. When the tip approaches the substrate or sample surface, photothermal force is generated. Therefore, the photothermal force in the PiFM system is mainly dominated by the photothermal dipole-dipole interaction force. As shown in Figure 1, the dipole of the tip is denoted as Pt with a polarizability αt, and the image dipole is denoted as pt' with a polarizability αt'. Assuming the dominant polarization direction is along the z-axis, the photothermal force generated along the z-axis direction can be expressed as: