Masanori Koshioka

Pattern formation and flow control of fine particles by laser-scanning micromanipulation

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.

Optical trapping of a metal particle and a water droplet by a scanning laser beam

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.

Three‐dimensional optical trapping and laser ablation of a single polymer latex particle in water

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.

Multibeam laser manipulation and fixation of microparticles

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.

Laser-scanning micromanipulation and spatial patterning of fine particles

Laser-scanning micromanipulation and spatial patterning of polystyrene latex or titanium dioxide particles in solution were demonstrated for the first time. A trapping laser beam was repetitionary scanned at 13~50 Hz by computer-controlled galvano mirrors to align micrometer-order particles along the pattern produced by the scanning laser beam. Characteristic features of the present technique are discussed.

Time-Dependent Fluorescence Depolarization Analysis in Three-Dimensional Microspectroscopy

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.

Three-Dimensional Space- and Time-Resolved Fluorescence Spectroscopy

A fluorescence spectroscopic system with both picosecond time resolution and submicrometer three-dimensional space resolution has been developed for elucidating the dynamics of inhomogeneous photophysical/photochemical phenomena. This system is based on a confocal laser scanning fluorescence microscope and a time-correlated single photon counting method. Results on demonstration experiments are shown to specify the performance of the system. Characteristics and limitations of the system are discussed.

Picosecond dynamics of excited singlet states in organic microcrystals: Diffuse reflectance laser photolysis study

Absorption spectra and picosecond dynamics of the singlet exciton states of benzil and p-terphenyl in a microcrystal have been measured for the first time by analyzing the diffuse reflected spectra of the picosecond continuum.

Confocal laser-induced absorption microscope

A new laser scanning microscope is proposed for imaging a three-dimensional absorption structure of a sample. The microscope is based on a confocal system built with excitation and absorption-monitoring lasers. The excitation laser produces excited molecules, and the absorption-monitoring laser probes their transient absorption. A three-dimensional optical transfer function of the microscope is theoretically derived to demonstrate a tomographic imaging capability. The spatial frequency cutoff is confirmed to be independent of the detector size. An experimental result is shown to verify the depth discrimination property.