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  4. Construction and Characterization of Optical Tweezer Embedded Differential Confocal Microscope
 
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Construction and Characterization of Optical Tweezer Embedded Differential Confocal Microscope

Date Issued
2004
Date
2004
Author(s)
Jan, I-Chien
DOI
zh-TW
URI
http://ntur.lib.ntu.edu.tw//handle/246246/53207
Abstract
In this thesis, an optical tweezer embedded differential confocal microscope system is developed. Base on the principle of differential confocal microscope and optical tweezer theory, the system is constructed and characterized. Some experimental results are carried out by the system and discussed. The main features of differential confocal microscopy include high depth resolution, large dynamic range, long working distance and high acquisition rate. The depth resolution of differential confocal microscopy in only limited by system noise. In the system build in this thesis, a depth resolution of 2 nm has been achieved. The dynamic range is as large as several micrometers, determined by wavelength of light source and numerical aperture of objective lens. Since probing the sample with far-field optical wave and without closed-loop locking the height of sample surface, differential confocal microscopy has advantage of high acquisition rate. The long working distance and large dynamic range features are suitable to measure the surface profile of high periodic structures. By collaborating with lateral detection element, resolution of ten nanometers in three-dimensional positioning has also been verified in the system. A homemade differential confocal microscope in upright configuration is constructed. The setup of the systems, specifications of elements and instruments, optical beam path configurations are also described in this thesis. The system noises, including mechanical vibration, optical background and electrical noise, are well analyzed and excluded. The signal to noise ratio of differential confocal signal is measured as high as 75 dB. If the wavelength is 633 nm, using the objective lens of 0.85 numerical aperture, the depth resolution is two nanometers. By the differential confocal microscope, wet-etched semi-conductor sample and the micro-cylinders in microfluidic channels are observed and compared with images taken with optical microscope and scanning electron microscope. Optical tweezer, as known as single beam optical tarp, grabs small particles of micrometer-size even nanometer-size by the force from photo momentum transfer. The main features of optical tweezer are non-contact and non-invasive. By combining optical tweezer and optical microscopes, one can manipulate the observed object in the microscopic scale. Ray optics model and electromagnetics model describe the model of optical trap, and the mathematical theory and simulation of ray optics model are introduced in this thesis. Upright and inverted configurations of optical tweezer embedded differential confocal microscopes are constructed. The Q value and the spring constant k of optical tweezer are characterized in the upright configuration system. In the setup constructed with inverted microscope, a quadrant photodiode is used to perform detection of lateral displacement. Combining with the depth resolution power of differential confocal microscope, three-dimensional positioning of a microsphere has been verified. Within 1-μm dynamic range in three axes, the resolutions of X, Y, and Z axes are 8 nm, 10 nm, 5 nm, respectively. By measuring the power spectrum density of silica bead trapped in optical tweezer, the cut-off frequency of Lorentz distribution is fitted. With the cut-off frequency and the spring constant k, the coefficient of viscosity of water is estimated in the experiment, of the error within 1% from the standard value. Combining the configuration of differential confocal microscopy and the optical tweezer, with sensitive lateral displacement detector, the system shows good potential on microrheology studies from the characterization in this thesis.
Subjects
光鉗
差動共焦顯微術
optical tweezer
differential confocal microscope
Type
thesis

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