ORCID Identifier(s)

0000-0001-7790-8576

Graduation Semester and Year

2018

Language

English

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Alan P Bowling

Abstract

Optical tweezers can hold and manipulate microscopic objects with the use of a highly focused laser beam. The radiation pressure acting on the object is generally in the range of piconewtons and can be attractive or repulsive based on the reflective indexes of the object and the surrounding medium. Though the advances in the field of Optical tweezers have been enormous in the past few years, only the object's planer motion can be analyzed with the motion capture technology available today. Due to the wide applications of Optical tweezers in the field of biology and physics, the ability to simulate the motion of these microscopic objects can help gather more data about object's motion and other related characteristics. One of the major issues related to simulating microscopic objects is the long computation time due to large accelerations. Because the mass of the object is extremely small, even very small amount of force can generate large accelerations resulting in smaller step sizes for numerical integration. This thesis discusses a method to calculate laser beam force acting on the microscopic object. It also discusses equations of motion of the object. The disproportionality caused due to large forces and small mass is mostly addressed by the use of famous overdamped Langevin equations, which omit the inertial properties in the equations of motion. However, this first order model is inconsistent with Newton's second law. A method of multiple scales is introduced which solves this problem by bringing all the terms of equations of motion in proportion with each other thus increasing the time step and reducing computation time. The proposed method was also validated with experiments done on three polystyrene beads with 500nm, 990nm, and 1950nm diameters. A brief discussion is given in the results section about the underdamped behavior of 500nm bead and the significance of low Reynolds number at such small length scale.

Keywords

Optical trap, Optical tweezer, Dynamics, Multi-scale, Method of multiple scales, Perturbation problems, Euler parameters, Equations of motion, Geometric optics, Underdamped motion

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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