Optical Tweezers Without the Price Tag: HeNe Trapping on an Open-Source Microscope

Optical tweezers are a cornerstone technique in atomic, molecular, and biological physics, yet their implementation typically relies on expensive infrared lasers and commercial microscope platforms, limiting access outside of research universities. We report the development of a cost-effective optical tweezing system built using a HeNe laser and an OpenFlexure inverted microscope, designed and implemented by high school students within a research-intensive laboratory environment. Our system adapts the open-source OpenFlexure microscope architecture to meet the optical alignment and numerical aperture requirements necessary for stable three-dimensional trapping using a visible-wavelength HeNe laser. Careful attention was given to beam conditioning, alignment tolerances, and objective selection. Using this platform, we demonstrate successful optical trapping of micron-scale dielectric particles and assess trap stability through controlled perturbations and displacement observations. The use of a HeNe laser presents both technical challenges and pedagogical advantages, requiring students to directly engage with wavelength-dependent trapping forces, scattering effects, and power limitations. These constraints motivate careful experimental design and provide a rich framework for connecting theory with hands-on measurement. The broader goal of this work is to establish an optical tweezing platform that can be inexpensively replicated by high schools and small colleges, enabling students not only to learn optical trapping techniques but also to perform meaningful measurements that contribute to ongoing scientific investigations. This project demonstrates that advanced AMO instrumentation can be made accessible without sacrificing experimental rigor, while simultaneously serving as a pathway for training the next generation of experimentally literate and research-ready scientists.