Dong Aotuo, Islam Md Shariful, Albin Sacharia, Deo Makarand
Annu Int Conf IEEE Eng Med Biol Soc. 2020 Jul;2020:2213-2216. doi: 10.1109/EMBC44109.2020.9176338.
The Refractive Index (RI) is an important parameter of characterizing optical properties of particles. In a dual-beam optical trap, two counter-propagating laser beams are used to trap micro-particles suspended in an aqueous medium. When a ray of light passes from one medium of lower RI (e.g. aqueous suspension medium) to another medium of higher RI (e.g. suspended particle), its momentum changes which exerts a proportional trapping force on the surface of the particle. Thus, accurate knowledge of RI of the particles and the surrounding medium is needed to determine the behavior of particles in an optical trap. The RI of micro-sized beads can be experimentally measured using traditional optical methods such as absorption microscopy. We developed an alternative theoretical method to estimate the RI of trapped particles based on non-contact optical trapping experimental outcomes. In our study, a theoretical model was formulated based on the experimentally measured minimum trapping powers for polystyrene and polyethylene beads using a dual-beam optical setup. The tendencies of trapping power-RI curves predicted by our model agreed very well with those measured experimentally. Our technique provides an alternative approach to determining the RI of a certain micro-size particle regardless of its size or density. Our method is especially advantageous over traditional methods to determine RI of biological particles which exhibit significant variations based on physiological and environmental conditions.
折射率（RI）是表征颗粒光学性质的一个重要参数。在双光束光阱中，两束反向传播的激光束用于捕获悬浮在水介质中的微粒。当一束光线从折射率较低的一种介质（如水悬浮介质）进入折射率较高的另一种介质（如悬浮颗粒）时，其动量会发生变化，这会在颗粒表面施加一个成比例的捕获力。因此，需要准确了解颗粒和周围介质的折射率，以确定颗粒在光阱中的行为。微米级珠子的折射率可以使用传统光学方法（如吸收显微镜）通过实验测量。我们基于非接触光阱实验结果开发了一种替代性理论方法来估算被捕获颗粒的折射率。在我们的研究中，使用双光束光学装置，基于对聚苯乙烯和聚乙烯珠子实验测量的最小捕获功率建立了一个理论模型。我们模型预测的捕获功率-折射率曲线趋势与实验测量结果非常吻合。我们的技术提供了一种确定特定微米级颗粒折射率的替代方法，而无需考虑其大小或密度。我们的方法相对于传统方法在确定生物颗粒折射率方面具有特别的优势，因为生物颗粒的折射率会根据生理和环境条件发生显著变化。
