Micro-assembly with a focused laser beam

One of the more challenging aspects of microelectromechanical systems is the assembly and inspection of microparts. Self-assembled devices would be preferred, however, for many devices this will not be possible, Inspection and trapping of parts using laser light pressure presents a possible solution to the problem of automated assembly. This paper presents preliminary results-for the optical trapping of microparts. Optical trapping and manipulation of microspheres and living biological cells that are transparent at the laser's wavelength has become an established technology. Visibly transparent microspheres ranging in size from 1 um to 25 um have been individually trapped and accumulated with single and multiple beams. Scanning of a focused beam in two-dimensional patterns has successfully led to the trapping of collections of spheres with demonstrations of group motion within the pattern and selective size separation. The trapping and welding together of two reflecting microspheres has also been performed. The manipulation of non-spherical microstructures in three dimensions to form micro-machines is still a matter of experimentation. Microstructures that include transparent spheres, geometrically symmetric siliceous micro-shells, and metallic gears, cylinders and cubes are investigated for their stability in-liquid under the optical force of focused laser beams. The structure's outer dimensions range in size from 5 um to 300 um. Laser wavelengths from the visible to the mid-range infrared are applied to optimize the target's transmittance or reflectance. Formula development for an optical momentum field and target interaction provides a force calculation method that is presented for structures with reflecting surfaces.