A novel micromanipulation technique is proposed for aligning fine particles on micrometer-scale spatial patterns and for moving the particles continuously along the formed patterns. This technique is based on the repetitive scanning of a focused trapping laser beam. The velocity of the particle flow can be controlled by scan speed and laser power. The origin of the driving force is considered theoretically and experimentally.

Laser trapping of a metal particle in water or a water droplet in liquid paraffin, which cannot be attained by irradiation of a TEM00 mode focused laser beam, was experimentally confirmed based on a scanning laser trapping technique. Although a metal particle or a water droplet experiences repulsive radiation force from a laser beam (1064 nm, focused into a ∼1 μm spot), scanning of the laser beam circularly around the particle was successful to optically trap and tweezer the particle. Water and ethylene glycol droplets dispersed in liquid paraffin were also shown to be manipulated independently by scanning double laser-beam trapping.

We developed a laser trapping-ablation system comprised of CW and pulsed Nd3+:YAG lasers as well as of an optical microscope. Three-dimensional manipulation of various kinds of particles and laser ablation of a single optically trapped, poly(methyl methacrylate) latex particle in water were demonstrated. A minute hole with its diameter of ∼sub-μm was fabricated on the latex particle (∼6 μm diameter). The hole size produced was much smaller than the effective diameter of the excitation laser beam, suggesting nonlinear optical (self-focusing of the laser beam) and photochemical (multiphoton absorption) mechanisms for the present laser trapping ablation. Characteristic features of the laser trapping-ablation are discussed in detail.

Three-dimensional space- and time-resolved fluorescence depolarization spectroscopy has been developed for elucidating picosecond rotational relaxation processes occurring in micrometer-sized volumes. Anisotropy decays are obtained by a new analytical method which is adapted to the large-solid-angle characteristic of the microscope optics. System parameters introduced in this method were determined by measuring a reference sample. The fluorescence dynamics of p-terphenyl in a thin liquid layer was analyzed as a demonstration experiment.

A multibeam laser trapping–reaction system was developed to demonstrate independent manipulation of plural microparticles as well as to induce photochemical reaction in a laser-trapped particle(s). Photopolymerization of vinyl monomers dissolved in a sample solution was employed to fix polystyrene latex particles regularly aligned by laser trapping. Integrated latex structures created by the successive manipulation/polymerization procedures were also shown to be freely manipulated by laser beams.