Design and Application of In-focus and Off-focus
|Keywords:||雷射鑷夾;散焦雷射鑷夾;準焦雷射鑷夾;捕捉一群微粒子;雷射鑷夾系統設計;樣品濃縮;捕捉力與捕捉範圍實驗;電磁波模型;optical tweezers;In-focus optical tweezers;Off-focus optical tweezers;capture a group of particles;Design of optical tweezers system;sample concentration;Trapping force and trapping range experiment;EM model of optical tweezers|
In the past decade, optical tweezers, which is capable of capturing micro objects via the gradient force produced by a converging laser beam, have been widely used in the capture, move, and manipulation of microbiological objects and micro particles. Typically, the force generated by an optical tweezers system is of the order of pico-Newton (10-12 N). The sizes of captured tiny objects range from a few tens of nano-meters to a few tens of micrometers. Optical tweezers have just become an important and powerful tool in biotechnology research. Traditionally, an optical tweezers system is operated by precisely focusing a laser beam into a focal point on the sample plane, which we call an in-focus optical tweezers system. It is commonly used to capture and manipulate a single particle at a time. In order to capture more particles in a short period of time, we innovate an off-focus optical tweezers system for the first time, which captures a group of micro particles at a time. In this thesis, we purposely shift the laser focal point slightly away from the sample plane. This leaves a relatively larger laser spot on the sample plane, which increases the capturing range. In this work, we will show the manipulation of a single polystyrene bead, a pseudomonas aeruginosa, and a spermatozoon, separately, by an in-focus optical tweezers system. Also, we will demo the capture of a group of polystyrene beads by an off-focus optical tweezers system. Based on the EM model of optical tweezers, we simulate the capturing range and the capturing force for the in-focus optical tweezers and the off-focus optical tweezers, separately. Besides, we also design an experiment to measure the relationship between the drift velocity of the solution relative to the captured beads and the capturing range by an optical tweezers system. The variation of the drift velocity clearly illustrates the relationship between the capturing range and the capturing force of an optical tweezers system. We conclude that the off-focus optical tweezers system has a longer trapping range but a weaker trapping force than the traditional in-focus optical tweezers system does. At last, we propose a design for sample concentration utilizing the off-focus optical tweezers. In addition, we present a detailed guideline for the design of optical tweezers. This may be helpful for those who are interested in setting up an optical tweezers system. We hope that this thesis is not only a useful reference on optical tweezers, but also a stimulation for further applications.
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