Browsing by Author "Chang, Ai-Tang"

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Fast trapping force calculation by utilizing graphic processing unit
(2012)
Tseng, Sheng-Yang
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Chang, Ai-Tang
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Luo, Chih-Wei
;
Hsu, Long
;
Kobayashi, Takayoshi
Fast calculation of trapping force provides a more direct way for optimizing designs of optical systems which generate optical traps. In this study, a graphic processing unit (GPU), NVIDIA GTX 275, is used to boost the speed of trapping efficiency calculation under ray optics approximation. The codes of trapping efficiency calculation are implemented in C++. The computing power of GPU is utilized through compute unified architecture device (CUDA) toolkit 4.0. The computing speed is compared with that of central processing unit (CPU), Intel Core 2 Quad Q9550. Over 100x speedup is achieved when single-precision floating-point numbers were used in the calculation.
Optical guiding with cylindrical mirror system
(2010)
Chang, Ai-Tang
;
Tseng, Sheng-Yang
;
Hsu, Long
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電子物理學系
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Department of Electrophysics
We proposed a method to guide micro-particles within a millimeter region. A cylindrical mirror is used to create an optical line segment for guiding particles. In order to increase the numerical aperture, Polydimethylsiloxane (PDMS) is poured on the cylindrical mirror. At the top of the PDMS layer, a fluidic channel is fabricated. As a collimated laser beam is incident on the cylindrical mirror, the laser beam is tightly focused and is transformed into a line-shaped pattern in the fluidic channel. In this way, a simple and cost-effective optical guiding system can be achieved.
Optimization of probe-laser focal offsets for single-particle tracking
(1970-01-01)
Chang, Ai-Tang
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Chang, Yi-Ren
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Chi, Sien
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Hsu, Long
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電子物理學系
"In optical tweezers applications, tracking a trapped particle is essential for force measurement. One of the most popular techniques for single-particle tracking is achieved by analyzing the forward and backward light pattern, scattered by the target particle trapped by a trap laser beam, of an additional probe-laser beam with different wavelength whose focus is slightly apart from the trapping center. However, the optimized focal offset has never been discussed. In this paper, we investigate the tracking range and sensitivity as a function of the focal offset between the trapping and the probe-laser beams. As a result, the optimized focal offsets are a 3.3-fold radius ahead and a 2.0-fold radius behind the trapping laser focus in the forward tracking and the backward tracking, respectively. The experimental result agrees well with a theoretical prediction using the Mie scattering theory. (C) 2012 Optical Society of America"
The single particle tracking system
(2010)
Chang, Ai-Tang
;
Chang, Yi-Ren
;
Chi, Sien
;
Hsu, Long
;
電子物理學系
In an optical tweezers system, the force measurement with a resolution less than pico-Newton can be achieved by precise measurement and analysis of the trapped particle trajectory. Typically, this single particle tracking technique is realized by a quadrant position sensor which detects the scattering lights of the trapping laser beam from the trapped particle. However, as the radius of the trapped particle is larger than the wavelength of the trapped laser, the scattering pattern becomes complicated, and it limits the tracking region and the signal sensitivity on the trapped particle. To solve this issue, an extra probing laser with optimized focal offset according to the trapping laser is applied to improve the flexibility and performance of our particle tracking system for each particle size. A rule of thumb between the optimized focal offsets and particle size is also concluded from the experimental results and theoretical simulations.