We have developed an optical cross-sectional imaging method for turbid media with the aid of a pulse ultrasound wave. Observation of deep regions in turbid media, such as tissue samples, is difficult owing to the rapid dispersion of an incoming laser beam by scattering. A pulse ultrasound wave, which is less scattered in tissues, can indicate the measuring point on the basis of the change of the optical scattering properties in a localized region. A depth-resolving capability can be achieved from the time-dependent measurement of the scattered-light intensity as the pulse ultrasound wave propagates in the sample. We verified the method by observing absorptive objects embedded in silicone rubber and by obtaining the cross-sectional image of an absorbing object surrounded by a strong scattering medium.
A systematic study of the pre-breakdown conduction current pulses in transformer oil using static electric stresses showed that these pulses are very sensitive to test conditions. The pulses were found to depend on gap length, applied stress, temperature, electrode material and hydrostatic pressure. The distribution of the pulse heights was exponential, indicating the presence of a multiplication process in the liquid. It is suggested that the pulses are due to the ionization of microscopic gas bubbles by electrons emitted at the cathode.
Ultrasound-modulated optical parallel speckle measurement with stroboscopic illumination in a coaxial reflection system has been developed in order to investigate the biological speckle pattern behavior modulated by a pulsed-ultrasound wave propagating through strong scattering media. An optically absorptive object located at a distance of 5.0millimeters from the surface of a 10.0millimeter thick acoustically impedance-matched scattering media has been measured with submillimeter spatial resolution by detecting backscattered light with a charge-coupled device camera. In addition, a series of absorptive dependence measurements were also acquired.
Multilayered optical data storage using a spatial soliton, which has the potential to increase the number of recording layers, is proposed and experimentally investigated. A Ti:sapphire pulsed laser focusing near the surface of a Ce-doped Sr0.75Ba0.25Nb2O6 crystal generated a second-harmonic (SH) beam associated with the self-focusing fundamental laser and induced SH collision responses to the counterpropagating laser pulses. Using threshold controls, single-bit data were recorded with a domain-reversal technique at the collision point, and its data were read out through a quasi-phase-matched SH generation process enhanced at the reversed domains. Multilayered recording and selective data rerecording were also demonstrated.
Ultrasound-modulated optical spectroscopy within a coaxial system capable of attaining submillimeter spatial resolution has been developed to investigate scattering media spectroscopic properties at depths of several centimeters. By using stroboscopic illumination methods, a broad spectral bandwidth pulsed laser and a focused ultrasound pulse simultaneously irradiated a biological tissue phantom containing oxyhemoglobin and deoxyhemoglobin absorbers. The ultrasound-modulated optical spectroscopic images were synchronously acquired by a fiber optic spectrometer scanning in two dimensions. We have obtained the wavelength dependent ultrasound-modulated optical signals produced by the ultrasound interactions changing the distribution of scattered light through several different mechanisms and evaluated the proposed system.
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