Georgia Journal of Science

Article Title



In the so called optical trapping technique a bead is held suspended in an aqueous solution by the presence of a lasing system. The laser light provides a trapping potential, similar to a harmonic potential, with a stiffness constant that is related to the laser intensity. It is possible for the bead, therefore, to perform simple harmonic motion, albeit under the action of random forces due to thermal motion. Thus, we look at a simple model for the bead's motion as a function of time through the application of Newton's 2nd law in the presence of a spring force, a damping force, and a random force. Due to the fact that the suspended bead could actually be an organelle in a cell or be a cell, with very low mass, we look at what might the differences of a model with negligible mass be compared to the one when the mass is not ignored. We have experimental results of a 500 nm diameter carboxylate coated polystyrene bead trapped in a 980 nm laser beam with trap stiffness of 0.05 pN/nm. The bead position in the trap was determined by using a position detection diode having 10 nanometer spatial resolution and a time resolution of 0.5 milliseconds. We look at possible interpretation of this data with the above mentioned model.


SEEP Grant from UWG and the UWG Physics Department for support

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