Optical-fiber diameter determination by scattering at oblique incidence.

A new nondestructive method for determination of the outer diameter of optical fibers is described. The principle of this technique is based on observing interference maxima in the scattered light from a fiber that is side illuminated by a laser beam at oblique incidence. This technique is easy to implement and can be applied to a fiber with an inhomogeneous and large core.

Optical visualization of the velocity distribution in a laser-induced thermocapillary liquid flow.

A liquid film of black oil is heated by a cw Gaussian laser beam. This process gives rise to time-increasing, axisymmetric temperature distribution with a maximum in the laser-beam axis. Because the surface tension is decreasing function of temperature, a centrifugal stress gradient and concurrent liquid flow build up in the liquid surface. This phenomenon (known as laser-induced thermocapillary liquid flow) is visualized in the far field of the reflected laser beam, where images microscopic bubbles traveling with the liquid appear as bright spots. Time-resolved experimental records show that the bubbles's images follow rectilinear trajectories at an approximately constant speed. This result is explained by using the theoretical expression of velocity distribution in thermocapillary liquid flow.

Transient deformation of liquid surfaces by laser-induced thermocapillarity.

Heavy hydrocarbons are irradiated with a Gaussian laser beam. The time-varying temperature distribution induced in the fluid gives rise to a surface-tension distribution. The later gives rise in turn to an accompanying liquid flow and surface-height distribution. In this paper, the time-varying shape of the induced depression is calculated as a function of the power distribution in the laser beam and of the thermal and mechanical properties of the material. The intensity distribution in the laser beam reflected from the depression is also calculated. Good agreement is found with previous experimental results.

Self-holograms of laser-induced surface depressions in heavy hydrocarbons.

Among applications of lasers in the petroleum industry are samples of heavy oils heated by a He-Ne laser beam. It is shown that laser power concentrations as low as 1 mW/mm(2) induce noticeable changes in the form of the surface. The far-field diffraction pattern of the reflected wave can be considered as a self-hologram of the hole, with the paraxial focus of the bottom of the hole as a point reference source. Annular images corresponding to different zones of the hole are reconstructed by illuminating the hologram with a spherical wave. A geometrical model of the shape of the irradiated surface is proposed and compared with experimental data.