The determination of an effective radius of an optically trapped polystyrene microbead distribution near a water air interface
<p>The research aimed to determine the effective radius (r*) of a trapped polystyrene</p><p>microbead near a water-air interface and to develop a 3-dimensional piezostage control module for</p><p>optical trapping within micrometre...
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| Format: | thesis |
| Language: | eng |
| Published: |
2019
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| Subjects: | |
| Online Access: | https://ir.upsi.edu.my/detailsg.php?det=8690 |
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| Summary: | <p>The research aimed to determine the effective radius (r*) of a trapped polystyrene</p><p>microbead near a water-air interface and to develop a 3-dimensional piezostage control module for</p><p>optical trapping within micrometre range. This study involved the development of a control</p><p>program so called PZStage and the determination of r* near the water-air interface. PZStage was</p><p>developed on the LabVIEW platform to control laser focus location in the trapping medium. A 3 m</p><p>bead was trapped in water at several heights towards the free space in a special design test cell.</p><p>The temporal displacement data of the trapped bead was recorded by a quadrant photodiode (QPD) and</p><p>analysed by a custom made program namely OSCal to determine r*. PZStage was well developed which</p><p>enabled precise laser focus control in 20 m range in three mutually orthogonal directions. The</p><p>result showed that r* was constant at any focus height at fixed water thickness and laser power.</p><p>Besides, r* depended on laser power at fixed laser focus height and water thickness in the form of</p><p>exponentially decaying relation. In conclusion, PZStage was successfully developed to precisely</p><p>control laser focus toward water-air interface, and the r* was found to be dependent on laser power</p><p>rather than laser focus height within the set experimental conditions. The research implied that</p><p>the low laser power was possible for optical trapping near the water-air interface with appropriate</p><p>water thickness selection. However, consideration must be taken into account since the trap was</p><p>shifted away from the laser focus as the focus height increases due to scattering</p><p>force.</p><p></p> |
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