Tomoharu Yamada

Simultaneous Measurement of Flow Velocities in Multipoint by the Laser Doppler Velocimeter

An important shortcoming of the conventional laser Doppler method is that it furnishes the instantaneous velocity at a single point in the fluid. To obtain the complete flow pattern, the experiment has to be repeated for different regions of the flow field (1) ~ (6).

Optical fiber heterodyne interferometer probe free from external disturbance

A fiber heterodyne interferometer probe free from external disturbance, which can measure small displacement of an object as a pressure transducer or a vibrational object, is described. The phase fluctuation in the fiber due to external disturbance is excluded using a reference beat signal of light beams from a reflection mirror on a graded index rod lens. A graded index‐type multimode fiber connected to one end of a single‐mode fiber by arc fusion splicing is used to improve acceptance of the light. The characteristics of the fiber probe are also described.

Electroplastic effect in Ca2+-doped KCl single crystals

Abstract The application of electric fields up to 6 MV m-1 reduces the flow stress during constant-strain-rate deformation of KCl containing 90 mol.p.p.m. Ca2+. These stress drops have been measured for various magnitudes and directions of electric field. It was found that the amount of stress drop is dependent on the component of electric field along the direction of Burgers vector. These effects are quantitatively interpreted by the charged-dislocation model which was first proposed by Whitworth in 1976 and which is modified in this paper. The charge values estimated in this model are 2.8 × 10−10Cm−1 for a rapidly cooled crystal and 1.9 × 10−10CM−1 for a slowly cooled crystal.

Optimization of the receiving optical system in the laser Doppler velocimeter for reduction of the sampling volume

A receiving optical system is described in which the scattered light beams are received through a projection lens by the pinhole of a photomultiplier. The depth Delta Z of the sampling volume in which the received scattered light beams are produced is calculated as a function of R/F, where R and F are the radius and focal length of the projection lens. Delta Z was also measured as a function of R/F; it is found that if the intersection angle of the laser beams is constant, then in order to make the sampling volume smaller, the magnification (M) of the lens should be increased, the radius (r) of the pinhole should be decreased, and R/F should be an optimum value.

New method for in-situ observation of moving dislocations in KCl crystal using laser-light scattering

Abstract The dislocations moving on slip planes in a KCl single crystal under an applied load were observed successfully by a 90° angle light scattering method using a high-power Ar-ion laser (2W for a wavelength of 514 nm). The photographs of stationary dislocations were taken by an scanning type optical microscope. The image of such dislocations was very sharp and uniform compared with that of grown-in dislocations. The dynamic behavior of moving dislocations was observed by an image intensifier to intensify the scattered light from dislocations. The motion of dislocations was jerkey under a constant load in almost all cases.

Flow visualization by an improved double exposure method in holography

Abstract Some optical differential interferometric techniques were investigated in order to measure the density distribution in the air jet flow of a small scale flow cell while excluding the effects of the optical distortion of its glass windows. A technique using moire fringe formation by rotating the reference wave in one exposure of the double exposure method was found to be most suitable for this purpose. High contrast and multiplication of moire fringes can be obtained by a moire fringe sharpening and multiplication method.

Streaked x-ray backlighting with twin-slit imager for study of density profile and trajectory of low-density foam target filled with deuterium liquid

Low-density plastic foam filled with liquid deuterium is one of the candidates for inertial fusion target. Density profile and trajectory of 527 nm laser-irradiated planer foam-deuterium target in the acceleration phase were observed with streaked side-on x-ray backlighting. An x-ray imager employing twin slits coupled to an x-ray streak camera was used to simultaneously observe three images of the target: self-emission from the target, x-ray backlighter profile, and the backlit target. The experimentally obtained density profile and trajectory were in good agreement with predictions by one-dimensional hydrodynamic simulation code ILESTA-1D.