Measurement of Spring Constant of Optical Tweezers using Boltzmann Distribution Method and Power Spectrum Density Method

• Main Authors: Wei-lien Sung, 宋偉廉
• Other Authors: 何正榮
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/28188774120963807916

碩士 === 國立中正大學 === 光機電整合工程所 === 97 === In this thesis, the historical background and development of an optical tweezers system were first reviewed. The introductory concepts for the basics of trapping a particle, the fundamental principles of operations and the detailed components for a typical optical tweezers were also presented. Subsequently, trapping and manipulation of polystyrene micro particles, bundles of polymer nanowires, and yeast cells were executed and demonstrated by an optical tweezers system set in lab. To describe the trapping force of an optical tweezers system quantitatively, characterization of the system’s spring constant was crucial. The main focus of this study was thus placed on precisely calibrating the spring constant of an optical tweezers system. The particle grasped by an optical tweezers is analogous to the way a particle was trapped in a potential well. Based on descriptions of the Brownian motion, both the Boltzmann distribution method and the power spectrum density method were employed to measure the spring constant. And, based on the employed optical tweezers system for trapping a polystyrene particle with diameter of 2.88um and under an laser power of 70 mW, the characterized spring constants for the two methods were 21.16±3pN/um and 19.96±2.6pN/um, respectively. Quantitatively, they were very close. Results further showed that the spring constant was increased linearly with the enhancement of the laser power. The effect of the particle size on the spring constant was also studied and discussed in this study. Once the spring constant is precisely calibrated, the optical tweezers system can be applied more directly to precision measurements and micro fabrications.