We design and implement a low-cost, modular integrated optical and atomic force microscope (AFM) based on an optical pickup unit (OPU) capable of stable contact-mode operation. By exploiting the inherent fixed conjugate planes within the OPU, we overcome the imaging difficulties caused by unfixed focal planes. This allows for real-time optical observation of the AFM probe position and the relative tip-sample position during operation with an optical resolution of 1.5 μm. Furthermore, by optimizing the circuit design and scanning logic, we suppress the OPU lens drift and system noise on imaging, enabling stable contact-mode operation with a signal noise of less than 2 nm. Built with off-the-shelf low-cost mechanical and electronic components alongside a few custom 3D-printed parts, this system features low cost, easy assembly, and high expandability.
Wang et al. (Sun,) studied this question.