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.
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.
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.