Tsuyoshi Ushizaka

Time-resolved measurement system of electrofluorescence spectra

A time-resolved measurement system for electrofluorescence spectra (plots of electric-field-induced change in fluorescence intensity as a function of wavelength) has been constructed by combining the time-correlated single-photon-counting system for emission decay measurement with modulated electric field as a sample bias. Four fluorescence decays, which correspond to positive, zero, negative, and zero sample bias, respectively, can be measured simultaneously, and a small field-induced change in decay profile can be detected precisely by using the constructed system. Measurements of time-resolved electrofluorescence spectra have been performed in electron donor–acceptor compounds which show a photoinduced electron transfer.

Measurements of flow velocity in a microscopic region using a transmission grating

This paper reports a method for measuring flow velocity in a microscopic region using a transmission grating. The flow velocity is determined from the measurement of moving particle images on a transmission grating placed in front of a photodetector. These images, formed by a microscopic objective, correspond to particles moving in a flow. The method is used to measure the spatial distributions of the flow velocity in small glass tubes and to compare some of the results with comparable data obtained with differential laser Doppler velocimetry. The resultant distributions are compared with the theoretical flow distributions obtained using the flow rates through the tubes. The results demonstrate that the transmission grating method is useful for measurements of the flow velocity in small probe volumes.

Zero-crossing study on dynamic properties of speckles

The zero-crossing problem is studied for the purpose of investigating the dynamic properties of speckle produced in the diffraction field by a moving diffuse object under illumination of coherent light. The zero-crossing method is applied to the time-differentiated speckle intensity fluctuations and studied in some detail with respect to the influence of noise and the low-pass filter used for suppressing the noise. From the theoretical and experimental studies, the velocity of the moving object is found to be accurately determined by measuring the number of zero-crossings per second of the time-differentiated speckle intensity fluctuations when both the optical configuration used for producing speckles and the characteristic of the low-pass filter for suppressing the noise are known beforehand.

Velocity measurement of the diffuse object based on time-differentiated speckle intensity fluctuations

Abstract This paper proposes a new velocity measuring method for a moving diffuse object on the basis of the autocorrelation of time-differentiated speckle intensity fluctuations. The theoretical background and experimental verification of this method are given. The correlation length of time-differentiated speckle intensity fluctuations is defined by the point at which the correlation becomes zero. By means of the correlation length the object velocity is found to be accurately measured.

Measurements of flow velocity in a microscopic region using a transmission grating: a differential type.

A method is described for measuring flow velocity in a microscopic region by means of a differential-type laser velocimeter with a transmission grating. The principle of this velocimeter is described on the basis of spatial filtering of the transmission grating. The filtering characteristics are theoretically analyzed using a power spectral density function. The velocimeter is used to measure flow velocities and their spatial distributions in a small (700-μm diam) glass tube. The theoretical and experimental results show that this differential-type velocimeter is more suitable and practical than the conventional one for measuring the flow velocity in a small probe.

Real-time generation of the Wigner distribution function by means of a single acousto-optic modulator

Abstract A new real-time optical processor is proposed for generating the Wigner distribution function of time signals. The optical system in the processor is simple since it only employs a single acousto-optic modulator. Verification of the present method is accomplished by means of an integrated detection system consisting of a scanning mirror, a photomultiplier, and an interface circuit. Experimental results are presented for cosine and chirp signals, and show a good agreement with the theory.

Measurements of velocity using a lenticular grating

A new method is reported for measuring the velocity using a lenticular grating. The principle of the method is theoretically described on the basis of transmission-grating velocimetry. The theoretical studies are performed to estimate the deflection and collection characteristics of the light passing through the lenticular grating. The method is used to measure the velocity of a rotating random pattern. The experimental results show the usefulness of the method for measurements of the velocity.

Measurements of flow velocity in a microscopic region using a transmission grating: a practical velocimeter.

This paper reports a practical differential-type transmission-grating velocimeter system for measuring the flow velocity in a microscopic region. This practical velocimeter is constructed with a useful optical system and an improved signal-analyzing system; it is used for measurements of the flow velocity in a biological field. The velocimeter also measures moving rough surfaces in a small probe area. The experimental results show the applicability of the transmission-grating velocimeter to measurements of blood flow velocity and to the velocities of various moving rough surfaces in a microscopic region.

Measurements of flow velocity in a microscopic region using a transmission grating: elimination of directional ambiguity.

This paper describes a method of eliminating the directional ambiguity in the flow velocity measured in a microscopic region using a transmission grating. The opposite directions of the flow are discriminated from the phase relation between two output signals obtained from the two photodetectors with transmission gratings. The method is applied to measurements of flow velocity in a small (3-mm diam) glass tube. The experimental results verify the usefulness of the method for determining the flow direction in transmission grating velocimetry.

Optical reproduction of sounds from old phonographic wax cylinders

It is shown that reproduction of sounds from old wax cylinders using various optical methods gives quite excellent materials in optics education. The laser-beam reflection method is explained by the geometrical optics, and is further discussed on the basis of the diffraction theory. Various techniques for improving the quality of reproduced sounds are introduced. Fiber optics is used for reproduction of sounds in a low pressure stylus contacting method. Applications of the laser- beam reflection method to other analogue recordings are introduced.