Quantifying Trapping Forces in a Simplied Optical Tweezers Setup

Optical tweezers utilize the radiation pressure exerted by a single tightlyfocused beam of laser light to trap microscopic particles in three dimensions. Such devices are particularly useful in biological applications such as cell manipulation and studying molecular motors as a means of noninvasive manipulation. However, optical tweezers are generally considered to be complex and costly. The purpose of this research was to construct an inexpensive optical tweezers setup that could stably trap particles in all three dimensions. A new method for quantifying transverse trapping forces with the drag force method was implemented, using a gradually accelerating stage driven by a motor and video analysis of the trapped particle. This project demonstrates that simple tweezers setups can be implemented in undergraduate or even high school laboratories and still achieve valid quantitative results. Inexpensive optical tweezers designs are more accessible for undergraduate and even high school research in biology and other fields, and their simple design provides a unique opportunity for academic learning about optical trapping. Our setup was also used to study the effect of altering the trapping beam’s intensity distribution on trapping efficiency, particularly by overfilling the aperture and creating annular beams of orders `=1-8.