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.
A modulated laser beam by a phase pattern exp(ilθ) can be focused by an objective into a ring-like optical vortex, where l is a constant and θ is the azimuth angle. The vortex is capable of trapping the particles nearby and circulating them along the ring. This phenomenon is often explained involving Fourier optics and the transfer of orbital angular momentum (OAM). Although Fourier optics transforms the electric field distribution of the modulated laser beam behind the phase pattern to that of the vortex, it does not include both the path and OAM of the photons of the electromagnetic wave. Therefore, it is difficult to further trace the transfer of OAM from the photons to the particles in the vortex. In this paper, we propose a simple and intuitive view to the origin of optical vortex. By analyzing the relationship of the intensity distributions between the phase of the phase pattern and the intensity of the vortex by utilizing Fourier transform, we propose that the phenomenon of vortex also involve the transfer of linear momentum on the vortex plane transversely.
In this paper, we propose an optical method for sorting micro-particles with holographic optical tweezers. By projecting an optical pattern onto the sample plane of a microscope via its objective, we can separate the sample particles of different sizes flowing to different directions.