Keiji Sasaki

Estimation of component spectral curves from unknown mixture spectra

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 has the advantage of providing a unique estimation of the component spectra, which helps chemists with quantitative analysis and further mathematical processing. Two experimental results demonstrate the effectiveness of the method: for infrared absorption spectra of xylene isomers and visible absorption spectra of dyes.

Constrained nonlinear method for estimating component spectra from multicomponent mixtures

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 sampling points subject to a priori information. Experimental results of the estimation of the infrared absorption spectra of xylene-isomer mixtures are shown; the noise problem with this method is also discussed.

Component analysis of spatial and spectral patterns in multispectral images. I. Basis

A new (to our knowledge) theory of component pattern analysis in multispectral images is developed by using the methods of principal component analysis and nonlinear optimization with a nonnegativity constraint. Given images of a scene in different color bands, we estimate both the spectral curves of components included in the image and the spatial pattern corresponding to each spectral curve. In this method, neither spatial nor spectral features of the components are necessary, but the physical rule of nonnegative absorptivity and density nonnegativity is used for any material of any optical frequency at any position in the image. Experimental results of component analysis with real microscopic image data are shown to demonstrate the effectiveness of the proposed method.

Three-dimensional Potential Analysis Of Radiation Pressure Exerted On A Single Microparticle

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 analysis based on the Boltzmann distribution. Characteristic features of the present system are discussed.

Optimal Wavelength Selection for Quantitative Analysis

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 formulation of the lower bound of the mean square errors for the combinations in a given subset is derived as a recurrence inequality. Experimental results of wavelength selection for infrared absorption spectra of xylene-isomer mixtures are shown to demonstrate the effectiveness of the algorithm in terms of computation complexity and accuracy in quantitative analysis for the fixed measurement time.

Advanced Algorithm for Determining Component Spectra Based on Principal Component Analysis

A method is proposed for determining the component spectra from a set of unknown two-component mixture spectra. This method is considered as an advanced version of the Lawton-Sylvestre self-modeling curve resolution. The disadvantage of the weakness against noise is overcome by the introduction of the concept of filtering; the uncertainty of the solution is removed by the reduction of the band for each curve to a single curve with aid of the concept of entropy minimization. Experimental results with infrared absorption spectra of xylene isomer mixtures and visible absorption spectra of dye mixtures demonstrate the power of this method.

Fluorescence dynamics of poly(N-vinylcarbazole) in solution as revealed by multicomponent analysis of picosecond time-resolved fluorescence spectra: dependence on tacticity and molecular weight

The steady-state fluorescence spectra of poly(N-vinylcarbazole) (PVCz) with various molecular weights in tetrahydrofuran solution were examined. The spectra of PVCz(r) prepared by radical polymerization were almost independent of the molecular weight, while those of PVCz(c) prepared by cationic polymerization were dependent on it. The difference in the temperature dependence of the spectra between PVCz(r) and PVCz(c) with high molecular weights was found. The time-resolved fluorescence spectra of PVCz(r) and PVCz(c) with high and low molecular weights were analysed by using a principal multicomponent spectral estimation method, whose results indicate clearly that the spectra were composed of only three component fluorescences (monomer, partial overlap excimer and sandwich excimer). The spectra were analysed by means of a least-squares fitting method using the three component spectral shapes, giving rise and decay curves of these component fluorescences. The curves were non-exponential and depended upon tacticity and the molecular weight. On the basis of these results, the excimer dynamics of PVCz in solution was discussed.

Manipulation of liquid crystal textures with a focused near infrared laser beam

Optical manipulation of disclinations and defects in liquid crystal films was demonstrated and discussed in terms of mass transfer induced by radiation pressure and of molecular rotation under the optical electric field. Orientation of liquid crystal molecules was controlled by changing the polarization direction of a focused cw laser beam. A disclination line could be deformed by moving the focal spot, just like drawing a bow. A point defect followed the laser beam so that it could be freely transported in the film. When two disclination points were optically manipulated to become fused, the defects disappeared immediately and did not return after switching off the laser.

Photon tunneling from an optically manipulated microsphere to a surface by lasing spectral analysis

Photon tunneling of lasing emission from a dye-doped microspherical particle to an object was investigated by use of a microspectroscopy system combined with a laser manipulation technique. An emission spectrum drastically changed with approaching the lasing microsphere to a glass plate. The intensity ratio between resonant peaks exhibited exponential dependence on the sphere-object distance, whose decay constant agreed with the penetration depth of an evanescent field just outside of the microsphere. The variation in the spectral profile can be explained with the Mie scattering theory. Applicability of the lasing microsphere as a probe of a near-field scanning optical microscope is discussed.

Component analysis of spatial and spectral patterns in multispectral images. II: Entropy minimization

In Part I [J. Opt. Soc. Am. A 4, 2101 (1987)] of this series, we developed a method for estimating both spatial patterns and spectral curves of components in a multispectral scene. This method does not need spatial and spectral information about the components but only multispread imagery data. The estimation is given as a feasible solution set satisfying the nonnegativity constraint for density and spectral response for all components at all pixels. In this paper, we estimate unique solutions for both the component patterns and the spectra from the feasible solution set. The solution is given by optimizing an entropy minimization criterion. This criterion enhances the spectral or spatial features of individual components. Two experimental results are shown to demonstrate the effectiveness of this method with biological and cytochemical specimens. The limitations of this method for unique pattern estimation are also discussed.