Particle manipulation and surface patterning by laser guidance

Laser-induced farces are used to manipulate atoms, clusters, and micron-sized particles in hollow optical fibers. Laser light (400 mW, 800 nm) is guided in a low-order grazing incidence mode in glass capillaries. The optical field in the fiber generates gradient and scattering forces which simultaneously draw particles to the center of the hollow region and push them along the fiber axis. Dielectric, semiconductor, and metal particles in the size range of 9 mu m-50 nm have been guided in gas- and liquid-filled fibers. Rb atoms are guided in evacuated fiber for up to 15 cm. Used alone or in conjunction with traditional methods, laser guidance is attractive for direct-write lithography. Arbitrary surface patterns can be created under ambient conditions with potential write speeds exceeding 10(6) particles/s and placement accuracy approaching 50 nm (assuming a 1 W laser, 100 nm Ge particles, and fiber filled with Ar at 760 Torr). Anisotropic optical forces resulting from particle shape anisotropy act to orient particles in the fiber. In initial experiments NaCl and KI crystals in aerosol suspension have been funneled into a hollow fiber using optical forces. The crystals have been directed onto a glass surface and lines as narrow as 0.5 mu m drawn. This linewidth is 30 times smaller than the inner fiber diameter and illustrates the strong focusing produced by. optical forces: Atomic force microscopy images show a high degree Of alignment between crystals suggesting that anisotropic optical forces act to orient the crystals during deposition. (C) 1998 American Vacuum Society. [S0734-211X(98) 12606-9].