Hokkaido University · Physics and Astronomy
Professor Keiji Sasaki's research lab specializes in optical manipulation and characterization of micro- and nanoscale materials, with a focus on laser-based micromanipulation, optical trapping, and in-situ spectroscopic analysis. The lab develops advanced techniques for precise control and patterning of particles, droplets, and functional materials using scanning laser beams, enabling applications in microfluidics, biosensing, and nanofabrication. Key research directions include all-optical bistability in hybrid waveguide systems, pH microprobing with fluorescent particles, and spectral unmixing of complex mixtures using multivariate analysis.
Figures are computed from collected data and may differ slightly.
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
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.
Two types of all-optical bistability were observed in polydiacetylene Langmuir–Blodgett (PDALB) films layered on rf-sputtered Corning 7059 slab-type waveguides with fused-quartz substrates. One bistability originating from optical nonlinear coupling between a prism and a PDALB-Corning hybrid waveguide produced input and output curves with hysteresis characteristics. The other type of bistability was observed in the hybrid waveguide with a nonlinear distributed-Bragg reflector of the PDALB top la
Abstract A novel pH microprobe has been developed, which makes it possible to measure inhomogeneous pH distributions with submicrometer three-dimensional resolution. A polyacrylamide particle incorporated with pH-sensitive fluorescein-acrylamide is manipulated with a laser trapping technique. It is demonstrated that the local pH in a water/glass interface is different from that of bulk water.
A method is described for estimating the spectra of pure components from the spectra of unknown mixtures with various relative concentrations. This method is based on principal component analysis and a constrained nonlinear optimization technique and is applicable to qualitative analysis of mixtures of more than three components. The method gives two curves as the estimate of a component spectrum: one consists of the set of the maxima and the other consists of the set of the minima for all sampl
In this paper, we propose a method which uniquely determines a set of single curves, each as an estimate of a component spectrum. No reference spectrum from a library is necessary; the spectrum set of mixtures of unknown components with various concentrations is used for the estimation of component spectral curves. The method is based on entropy minimization. In comparison with an earlier method [ Appl. Opt.22, 3599 ( 1983)], which gives the bands of the possible component spectra, this method h
A system that makes it possible to precisely and instantaneously observe a potential energy of laser trapping as a function of three-dimensional position was developed for analyzing radiation pressure acting on a single microparticle in solution. Position sensing with a quadrant photodiode and total internal reflection microscopy are applied for measuring thermal Brownian motion of the trapped particle with ∼10 nm resolution, and a trapping potential profile is estimated by a thermodynamical ana
Optical trapping and manipulation have been widely applied to biological systems, and their cutting-edge techniques are creating current trends in nanomaterial sciences. The resonant absorption of materials induces not only the energy transfer from photons to quantum mechanical motion of electrons but also the momentum transfer between them, resulting in dissipative optical forces that drive the macroscopic mechanical motion of the particles. However, optical manipulation, according to the quant
A new computer algorithm has been developed for selecting the optimal set of wavelengths for spectroscopic quantitative analysis of mixture samples. The method is based on the criterion of the minimum mean square error between concentrations of the mixture components and their estimates. The branch and bound algorithm finds the optimal set from all possible combinations of wavelengths. This algorithm saves computation time significantly, compared with the enumerative method. The mathematical for
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