Two sets of resonances in glass microspheres attached to a standard communication grade single mode optical fiber have
been observed. It has been found that the strength of the resonances depends strongly on the polarization of the coupled
light. Furthermore, the position of the resonances in the wavelength domain depends on the polarization of light in the
optical fiber with maximum magnitudes shifted by approximately 45°.
The trap length along the beam axis for an optical trap formed with an upright, oil-immersion microscope was
measured. The goals for this effort were twofold. It was deemed useful to understand the depth to which an optical
trap can reach for purposes of developing a tool to assist in the fabrication of miniature devices. Additionally, it was
desired to know whether the measured trap length favored one or the other of two competing theories to model an
optical trap. The approach was to trap a microsphere of known size and mass and raise it from its initial trap
position. The microsphere was then dropped by blocking the laser beam for a pre-determined amount of time.
Dropping the microsphere in a free-fall mode from various heights relative to the coverslip provides an estimate of
how the trapping length changes with depth in water in a sample chamber on a microscope slide. While it was not
possible to measure the trap length with sufficient precision to support any particular theory of optical trap
formation, it was possible to find regions where the presence of physical boundaries influenced optical traps, and
determine that the trap length, for the apparatus studied, is between 6 and 7 micrometers. These results allow more
precise control using optical micromanipulation to assemble miniature devices by providing information about the
distance over which an optical trap is effective.
A method is discussed for using neural networks to control optical tweezers. Neural-net outputs are combined with scaling and tiling to generate 480X480-pixel control patterns for a spatial light modulator (SLM). The SLM can be combined in various ways with a microscope to create movable tweezers traps with controllable profiles. The neural nets are intended to respond to scattered light from carbon and silicon carbide nanotube sensors. The nanotube sensors are to be held by the traps for manipulation and calibration. Scaling and tiling allow the 100X100-pixel maximum resolution of the neural-net software to be applied in stages to exploit the full 480X480-pixel resolution of the SLM. One of these stages is intended to create sensitive null detectors for detecting variations in the scattered light from the nanotube sensors.